Unwinder for x86*.

Signed-off-by: Jan Kratochvil <jan.kratochvil@redhat.com>
Signed-off-by: Mark Wielaard  <mjw@redhat.com>

36 files changed, 2623 insertions, 32 deletions

diff --git a/ChangeLog b/ChangeLog
index 0ef44168..df993090 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2013-11-07  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* configure.ac: New AC_CHECK_SIZEOF for long.  Call utrace_BIARCH, new
+	AC_SUBST for CC_BIARCH.
+
 2013-11-06  Mark Wielaard  <mjw@redhat.com>
 
 	* configure.ac (--enable-dwz): Add AC_MSG_WARN when disabled but
diff --git a/backends/ChangeLog b/backends/ChangeLog
index 28c807a9..3c57f8c3 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -1,3 +1,15 @@
+2013-11-07  Jan Kratochvil  <jan.kratochvil@redhat.com>
+	    Mark Wielaard  <mjw@redhat.com>
+
+	* Makefile.am (i386_SRCS): Add i386_initreg.c.
+	(x86_64_SRCS): Add x86_64_initreg.c.
+	* i386_initreg.c: New file.
+	* i386_init.c (i386_init): Initialize frame_nregs and
+	set_initial_registers_tid.
+	* x86_64_initreg.c: New file.
+	* x86_64_init.c (x86_64_init): Initialize frame_nregs and
+	set_initial_registers_tid.
+
 2013-10-06  Mark Wielaard  <mjw@redhat.com>
 
 	* ppc_cfi.c (ppc_abi_cfi): Use DW_CFA_val_offset for reg1, not
diff --git a/backends/Makefile.am b/backends/Makefile.am
index 557ed879..5b5e0676 100644
--- a/backends/Makefile.am
+++ b/backends/Makefile.am
@@ -50,7 +50,8 @@ libdw = ../libdw/libdw.so
 endif
 
 i386_SRCS = i386_init.c i386_symbol.c i386_corenote.c i386_cfi.c \
-	    i386_retval.c i386_regs.c i386_auxv.c i386_syscall.c
+	    i386_retval.c i386_regs.c i386_auxv.c i386_syscall.c \
+	    i386_initreg.c
 cpu_i386 = ../libcpu/libcpu_i386.a
 libebl_i386_pic_a_SOURCES = $(i386_SRCS)
 am_libebl_i386_pic_a_OBJECTS = $(i386_SRCS:.c=.os)
@@ -60,7 +61,8 @@ libebl_sh_pic_a_SOURCES = $(sh_SRCS)
 am_libebl_sh_pic_a_OBJECTS = $(sh_SRCS:.c=.os)
 
 x86_64_SRCS = x86_64_init.c x86_64_symbol.c x86_64_corenote.c x86_64_cfi.c \
-	      x86_64_retval.c x86_64_regs.c i386_auxv.c x86_64_syscall.c
+	      x86_64_retval.c x86_64_regs.c i386_auxv.c x86_64_syscall.c \
+	      x86_64_initreg.c
 cpu_x86_64 = ../libcpu/libcpu_x86_64.a
 libebl_x86_64_pic_a_SOURCES = $(x86_64_SRCS)
 am_libebl_x86_64_pic_a_OBJECTS = $(x86_64_SRCS:.c=.os)
diff --git a/backends/i386_init.c b/backends/i386_init.c
index cc9b2d7f..1e0b4863 100644
--- a/backends/i386_init.c
+++ b/backends/i386_init.c
@@ -1,5 +1,5 @@
 /* Initialization of i386 specific backend library.
-   Copyright (C) 2000-2009 Red Hat, Inc.
+   Copyright (C) 2000-2009, 2013 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <drepper@redhat.com>, 2000.
 
@@ -63,6 +63,9 @@ i386_init (elf, machine, eh, ehlen)
   HOOK (eh, auxv_info);
   HOOK (eh, disasm);
   HOOK (eh, abi_cfi);
+  /* gcc/config/ #define DWARF_FRAME_REGISTERS.  For i386 it is 17, why?  */
+  eh->frame_nregs = 9;
+  HOOK (eh, set_initial_registers_tid);
 
   return MODVERSION;
 }
diff --git a/backends/i386_initreg.c b/backends/i386_initreg.c
new file mode 100644
index 00000000..9e819a47
--- /dev/null
+++ b/backends/i386_initreg.c
@@ -0,0 +1,79 @@
+/* Fetch live process registers from TID.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#if defined __i386__ || defined __x86_64__
+# include <sys/types.h>
+# include <sys/user.h>
+# include <sys/ptrace.h>
+#endif
+
+#define BACKEND i386_
+#include "libebl_CPU.h"
+
+bool
+i386_set_initial_registers_tid (pid_t tid __attribute__ ((unused)),
+			  ebl_tid_registers_t *setfunc __attribute__ ((unused)),
+				void *arg __attribute__ ((unused)))
+{
+#if !defined __i386__ && !defined __x86_64__
+  return false;
+#else /* __i386__ || __x86_64__ */
+  struct user_regs_struct user_regs;
+  if (ptrace (PTRACE_GETREGS, tid, NULL, &user_regs) != 0)
+    return false;
+  Dwarf_Word dwarf_regs[9];
+# if defined __i386__
+  dwarf_regs[0] = user_regs.eax;
+  dwarf_regs[1] = user_regs.ecx;
+  dwarf_regs[2] = user_regs.edx;
+  dwarf_regs[3] = user_regs.ebx;
+  dwarf_regs[4] = user_regs.esp;
+  dwarf_regs[5] = user_regs.ebp;
+  dwarf_regs[6] = user_regs.esi;
+  dwarf_regs[7] = user_regs.edi;
+  dwarf_regs[8] = user_regs.eip;
+# elif defined __x86_64__
+  dwarf_regs[0] = user_regs.rax;
+  dwarf_regs[1] = user_regs.rcx;
+  dwarf_regs[2] = user_regs.rdx;
+  dwarf_regs[3] = user_regs.rbx;
+  dwarf_regs[4] = user_regs.rsp;
+  dwarf_regs[5] = user_regs.rbp;
+  dwarf_regs[6] = user_regs.rsi;
+  dwarf_regs[7] = user_regs.rdi;
+  dwarf_regs[8] = user_regs.rip;
+# else /* (__i386__ || __x86_64__) && (!__i386__ && !__x86_64__) */
+#  error "source file error, it cannot happen"
+# endif /* (__i386__ || __x86_64__) && (!__i386__ && !__x86_64__) */
+  return setfunc (0, 9, dwarf_regs, arg);
+#endif /* __i386__ || __x86_64__ */
+}
diff --git a/backends/x86_64_init.c b/backends/x86_64_init.c
index 67a58804..b885558b 100644
--- a/backends/x86_64_init.c
+++ b/backends/x86_64_init.c
@@ -1,5 +1,5 @@
 /* Initialization of x86-64 specific backend library.
-   Copyright (C) 2002-2009 Red Hat, Inc.
+   Copyright (C) 2002-2009, 2013 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <drepper@redhat.com>, 2002.
 
@@ -60,6 +60,9 @@ x86_64_init (elf, machine, eh, ehlen)
   HOOK (eh, auxv_info);
   HOOK (eh, disasm);
   HOOK (eh, abi_cfi);
+  /* gcc/config/ #define DWARF_FRAME_REGISTERS.  */
+  eh->frame_nregs = 17;
+  HOOK (eh, set_initial_registers_tid);
 
   return MODVERSION;
 }
diff --git a/backends/x86_64_initreg.c b/backends/x86_64_initreg.c
new file mode 100644
index 00000000..0c493640
--- /dev/null
+++ b/backends/x86_64_initreg.c
@@ -0,0 +1,73 @@
+/* Fetch live process registers from TID.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <stdlib.h>
+#ifdef __x86_64__
+# include <sys/user.h>
+# include <sys/ptrace.h>
+#endif
+
+#define BACKEND x86_64_
+#include "libebl_CPU.h"
+
+bool
+x86_64_set_initial_registers_tid (pid_t tid __attribute__ ((unused)),
+			  ebl_tid_registers_t *setfunc __attribute__ ((unused)),
+				  void *arg __attribute__ ((unused)))
+{
+#ifndef __x86_64__
+  return false;
+#else /* __x86_64__ */
+  struct user_regs_struct user_regs;
+  if (ptrace (PTRACE_GETREGS, tid, NULL, &user_regs) != 0)
+    return false;
+  Dwarf_Word dwarf_regs[17];
+  dwarf_regs[0] = user_regs.rax;
+  dwarf_regs[1] = user_regs.rdx;
+  dwarf_regs[2] = user_regs.rcx;
+  dwarf_regs[3] = user_regs.rbx;
+  dwarf_regs[4] = user_regs.rsi;
+  dwarf_regs[5] = user_regs.rdi;
+  dwarf_regs[6] = user_regs.rbp;
+  dwarf_regs[7] = user_regs.rsp;
+  dwarf_regs[8] = user_regs.r8;
+  dwarf_regs[9] = user_regs.r9;
+  dwarf_regs[10] = user_regs.r10;
+  dwarf_regs[11] = user_regs.r11;
+  dwarf_regs[12] = user_regs.r12;
+  dwarf_regs[13] = user_regs.r13;
+  dwarf_regs[14] = user_regs.r14;
+  dwarf_regs[15] = user_regs.r15;
+  dwarf_regs[16] = user_regs.rip;
+  return setfunc (0, 17, dwarf_regs, arg);
+#endif /* __x86_64__ */
+}
diff --git a/configure.ac b/configure.ac
index 03d5756f..99b74ae5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -326,4 +326,15 @@ esac
 # Round up to the next release API (x.y) version.
 eu_version=$(( (eu_version + 999) / 1000 ))
 
+AC_CHECK_SIZEOF(long)
+
+# On a 64-bit host where can can use $CC -m32, we'll run two sets of tests.
+# Likewise in a 32-bit build on a host where $CC -m64 works.
+utrace_BIARCH
+# `$utrace_biarch' will be `-m64' even on an uniarch i386 machine.
+AS_IF([test $utrace_cv_cc_biarch = yes],
+      [CC_BIARCH="$CC $utrace_biarch"],
+      [CC_BIARCH="$CC"])
+AC_SUBST([CC_BIARCH])
+
 AC_OUTPUT
diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index d4c1049d..c355c306 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,11 @@
+2013-11-07  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* cfi.h (struct Dwarf_Frame_s): Make the comment more specific.
+	* libdw.map (ELFUTILS_0.156): Add dwfl_attach_state, dwfl_pid,
+	dwfl_thread_dwfl, dwfl_thread_tid, dwfl_frame_thread,
+	dwfl_thread_state_registers, dwfl_thread_state_register_pc,
+	dwfl_getthreads, dwfl_thread_getframes and dwfl_frame_pc.
+
 2013-11-01  Michael Forney  <mforney@mforney.org>
 
 	* Makefile.am (libdwfl_objects): New definition.
diff --git a/libdw/cfi.h b/libdw/cfi.h
index 89498335..98ac6cfa 100644
--- a/libdw/cfi.h
+++ b/libdw/cfi.h
@@ -1,5 +1,5 @@
 /* Internal definitions for libdw CFI interpreter.
-   Copyright (C) 2009-2010 Red Hat, Inc.
+   Copyright (C) 2009-2010, 2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -150,8 +150,8 @@ struct dwarf_frame_register
   Dwarf_Sword value:(sizeof (Dwarf_Sword) * 8 - 3);
 };
 
-/* This holds everything we know about the state of the frame
-   at a particular PC location described by an FDE.  */
+/* This holds instructions for unwinding frame at a particular PC location
+   described by an FDE.  */
 struct Dwarf_Frame_s
 {
   /* This frame description covers PC values in [start, end).  */
diff --git a/libdw/libdw.map b/libdw/libdw.map
index 5fb6660e..922608ac 100644
--- a/libdw/libdw.map
+++ b/libdw/libdw.map
@@ -259,6 +259,16 @@ ELFUTILS_0.156 {
   global:
     # Replaced ELFUTILS_0.122 version, which has a wrapper without add_p_vaddr.
     dwfl_report_elf;
+    dwfl_attach_state;
+    dwfl_pid;
+    dwfl_thread_dwfl;
+    dwfl_thread_tid;
+    dwfl_frame_thread;
+    dwfl_thread_state_registers;
+    dwfl_thread_state_register_pc;
+    dwfl_getthreads;
+    dwfl_thread_getframes;
+    dwfl_frame_pc;
 } ELFUTILS_0.149;
 
 ELFUTILS_0.157 {
diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index dc599210..467b4869 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,4 +1,49 @@
 2013-11-07  Jan Kratochvil  <jan.kratochvil@redhat.com>
+	    Mark Wielaard  <mjw@redhat.com>
+
+	* Makefile.am (libdwfl_a_SOURCES): Add dwfl_frame.c, frame_unwind.c,
+	dwfl_frame_pc.c, linux-pid-attach.c, linux-core-attach.c and
+	dwfl_frame_regs.c.
+	* core-file.c (dwfl_core_file_report): Call
+	__libdwfl_attach_state_for_core.
+	* dwfl_end.c (dwfl_end): Call __libdwfl_process_free.
+	* dwfl_frame.c: New file.
+	* frame_unwind.c: New file.
+	* dwfl_frame_pc.c: New file.
+	* linux-pid-attach.c: New file.
+	* linux-core-attach.c: New file.
+	* dwfl_frame_regs.c: New file.
+	* libdwfl.h (Dwfl_Thread, Dwfl_Frame): New typedefs.
+	(dwfl_core_file_report, dwfl_linux_proc_report): Extend comments.
+	(Dwfl_Thread_Callbacks): New definition.
+	(struct ebl, dwfl_attach_state, dwfl_pid, dwfl_thread_dwfl)
+	(dwfl_thread_tid, dwfl_frame_thread, dwfl_thread_state_registers)
+	(dwfl_thread_state_register_pc, dwfl_getthreads, dwfl_thread_getframes)
+	(dwfl_frame_pc): New declarations.
+	* libdwflP.h (Dwfl_Process): New typedef.
+	(LIBEBL_BAD, CORE_MISSING, INVALID_REGISTER, PROCESS_MEMORY_READ)
+	(PROCESS_NO_ARCH, PARSE_PROC, INVALID_DWARF, UNSUPPORTED_DWARF)
+	(NEXT_THREAD_FAIL, ATTACH_STATE_CONFLICT, NO_ATTACH_STATE, NO_UNWIND)
+	(INVALID_ARGUMENT): New DWFL_ERROR entries.
+	(struct Dwfl): New entry process.
+	(struct Dwfl_Process, struct Dwfl_Thread, struct Dwfl_Frame)
+	(__libdwfl_frame_reg_get, __libdwfl_frame_reg_set)
+	(__libdwfl_process_free, __libdwfl_frame_unwind)
+	(__libdwfl_attach_state_for_pid, __libdwfl_attach_state_for_core)
+	(__libdwfl_segment_start, __libdwfl_segment_end): New declarations.
+	(dwfl_attach_state, dwfl_pid, dwfl_thread_dwfl, dwfl_thread_tid)
+	(dwfl_frame_thread, dwfl_thread_state_registers)
+	(dwfl_thread_state_register_pc, dwfl_getthreads, dwfl_thread_getframes)
+	(dwfl_frame_pc): New INTDECL entries.
+	* linux-proc-maps.c (dwfl_linux_proc_report): Call
+	__libdwfl_attach_state_for_pid.
+	* segment.c (segment_start): Rename to ...
+	(__libdwfl_segment_start): ... here and make it internal_function.
+	(segment_end): Rename to ...
+	(__libdwfl_segment_end): ... here and make it internal_function.
+	(reify_segments, dwfl_report_segment): Rename them at the callers.
+
+2013-11-07  Jan Kratochvil  <jan.kratochvil@redhat.com>
 
 	* core-file.c (dwfl_core_file_report): Remove the use of MAX.
 
diff --git a/libdwfl/Makefile.am b/libdwfl/Makefile.am
index 3ef4dd6b..ce590dac 100644
--- a/libdwfl/Makefile.am
+++ b/libdwfl/Makefile.am
@@ -2,7 +2,7 @@
 ##
 ## Process this file with automake to create Makefile.in
 ##
-## Copyright (C) 2005-2010 Red Hat, Inc.
+## Copyright (C) 2005-2010, 2013 Red Hat, Inc.
 ## This file is part of elfutils.
 ##
 ## This file is free software; you can redistribute it and/or modify
@@ -68,7 +68,9 @@ libdwfl_a_SOURCES = dwfl_begin.c dwfl_end.c dwfl_error.c dwfl_version.c \
 		    dwfl_module_return_value_location.c \
 		    dwfl_module_register_names.c \
 		    dwfl_segment_report_module.c \
-		    link_map.c core-file.c open.c image-header.c
+		    link_map.c core-file.c open.c image-header.c \
+		    dwfl_frame.c frame_unwind.c dwfl_frame_pc.c \
+		    linux-pid-attach.c linux-core-attach.c dwfl_frame_regs.c
 
 if ZLIB
 libdwfl_a_SOURCES += gzip.c
diff --git a/libdwfl/core-file.c b/libdwfl/core-file.c
index 4f669834..f9120ca9 100644
--- a/libdwfl/core-file.c
+++ b/libdwfl/core-file.c
@@ -1,5 +1,5 @@
 /* Core file handling.
-   Copyright (C) 2008-2010 Red Hat, Inc.
+   Copyright (C) 2008-2010, 2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -558,6 +558,13 @@ dwfl_core_file_report (Dwfl *dwfl, Elf *elf, const char *executable)
 
   clear_r_debug_info (&r_debug_info);
 
+  if (listed > 0)
+    {
+      /* Possible error is ignored, DWFL still may be useful for non-unwinding
+	 operations.  */
+      __libdwfl_attach_state_for_core (dwfl, elf);
+    }
+
   /* We return the number of modules we found if we found any.
      If we found none, we return -1 instead of 0 if there was an
      error rather than just nothing found.  */
diff --git a/libdwfl/dwfl_end.c b/libdwfl/dwfl_end.c
index 94fcfc6e..33cae48c 100644
--- a/libdwfl/dwfl_end.c
+++ b/libdwfl/dwfl_end.c
@@ -1,5 +1,5 @@
 /* Finish a session using libdwfl.
-   Copyright (C) 2005, 2008, 2012 Red Hat, Inc.
+   Copyright (C) 2005, 2008, 2012-2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -34,6 +34,9 @@ dwfl_end (Dwfl *dwfl)
   if (dwfl == NULL)
     return;
 
+  if (dwfl->process)
+    __libdwfl_process_free (dwfl->process);
+
   free (dwfl->lookup_addr);
   free (dwfl->lookup_module);
   free (dwfl->lookup_segndx);
diff --git a/libdwfl/dwfl_frame.c b/libdwfl/dwfl_frame.c
new file mode 100644
index 00000000..11376c6e
--- /dev/null
+++ b/libdwfl/dwfl_frame.c
@@ -0,0 +1,345 @@
+/* Get Dwarf Frame state for target PID or core file.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#include "libdwflP.h"
+#include <sys/ptrace.h>
+#include <unistd.h>
+
+/* Set STATE->pc_set from STATE->regs according to the backend.  Return true on
+   success, false on error.  */
+static bool
+state_fetch_pc (Dwfl_Frame *state)
+{
+  switch (state->pc_state)
+    {
+    case DWFL_FRAME_STATE_PC_SET:
+      return true;
+    case DWFL_FRAME_STATE_PC_UNDEFINED:
+      abort ();
+    case DWFL_FRAME_STATE_ERROR:
+      {
+	Ebl *ebl = state->thread->process->ebl;
+	Dwarf_CIE abi_info;
+	if (ebl_abi_cfi (ebl, &abi_info) != 0)
+	  {
+	    __libdwfl_seterrno (DWFL_E_LIBEBL);
+	    return false;
+	  }
+	unsigned ra = abi_info.return_address_register;
+	/* dwarf_frame_state_reg_is_set is not applied here.  */
+	if (ra >= ebl_frame_nregs (ebl))
+	  {
+	    __libdwfl_seterrno (DWFL_E_LIBEBL_BAD);
+	    return false;
+	  }
+	state->pc = state->regs[ra];
+	state->pc_state = DWFL_FRAME_STATE_PC_SET;
+      }
+      return true;
+    }
+  abort ();
+}
+
+/* Do not call it on your own, to be used by thread_* functions only.  */
+
+static void
+state_free (Dwfl_Frame *state)
+{
+  Dwfl_Thread *thread = state->thread;
+  assert (thread->unwound == state);
+  thread->unwound = state->unwound;
+  free (state);
+}
+
+static void
+thread_free_all_states (Dwfl_Thread *thread)
+{
+  while (thread->unwound)
+    state_free (thread->unwound);
+}
+
+static Dwfl_Frame *
+state_alloc (Dwfl_Thread *thread)
+{
+  assert (thread->unwound == NULL);
+  Ebl *ebl = thread->process->ebl;
+  size_t nregs = ebl_frame_nregs (ebl);
+  if (nregs == 0)
+    return NULL;
+  assert (nregs < sizeof (((Dwfl_Frame *) NULL)->regs_set) * 8);
+  Dwfl_Frame *state = malloc (sizeof (*state) + sizeof (*state->regs) * nregs);
+  if (state == NULL)
+    return NULL;
+  state->thread = thread;
+  state->signal_frame = false;
+  state->initial_frame = true;
+  state->pc_state = DWFL_FRAME_STATE_ERROR;
+  memset (state->regs_set, 0, sizeof (state->regs_set));
+  thread->unwound = state;
+  state->unwound = NULL;
+  return state;
+}
+
+void
+internal_function
+__libdwfl_process_free (Dwfl_Process *process)
+{
+  Dwfl *dwfl = process->dwfl;
+  if (process->callbacks->detach != NULL)
+    process->callbacks->detach (dwfl, process->callbacks_arg);
+  assert (dwfl->process == process);
+  dwfl->process = NULL;
+  if (process->ebl_close)
+    ebl_closebackend (process->ebl);
+  free (process);
+}
+
+/* Allocate new Dwfl_Process for DWFL.  */
+static void
+process_alloc (Dwfl *dwfl)
+{
+  Dwfl_Process *process = malloc (sizeof (*process));
+  if (process == NULL)
+    return;
+  process->dwfl = dwfl;
+  dwfl->process = process;
+}
+
+bool
+dwfl_attach_state (Dwfl *dwfl, int machine, pid_t pid,
+		   const Dwfl_Thread_Callbacks *thread_callbacks, void *arg)
+{
+  if (thread_callbacks == NULL || thread_callbacks->next_thread == NULL
+      || thread_callbacks->set_initial_registers == NULL)
+    {
+      __libdwfl_seterrno (DWFL_E_INVALID_ARGUMENT);
+      return false;
+    }
+  if (dwfl->process != NULL)
+    {
+      __libdwfl_seterrno (DWFL_E_ATTACH_STATE_CONFLICT);
+      return false;
+    }
+  Ebl *ebl;
+  bool ebl_close;
+  if (machine != EM_NONE)
+    {
+      ebl = ebl_openbackend_machine (machine);
+      ebl_close = true;
+    }
+  else
+    {
+      ebl = NULL;
+      for (Dwfl_Module *mod = dwfl->modulelist; mod != NULL; mod = mod->next)
+	{
+	  /* Reading of the vDSO module may fail as /proc/PID/mem is unreadable
+	     without PTRACE_ATTACH and we may not be PTRACE_ATTACH-ed now.
+	     MOD would not be re-read later to unwind it when we are already
+	     PTRACE_ATTACH-ed to PID.  */
+	  if (strncmp (mod->name, "[vdso: ", 7) == 0)
+	    continue;
+	  Dwfl_Error error = __libdwfl_module_getebl (mod);
+	  if (error != DWFL_E_NOERROR)
+	    continue;
+	  ebl = mod->ebl;
+	  break;
+	}
+      ebl_close = false;
+    }
+  if (ebl == NULL)
+    {
+      /* Not identified EBL from any of the modules.  */
+      __libdwfl_seterrno (DWFL_E_PROCESS_NO_ARCH);
+      return false;
+    }
+  process_alloc (dwfl);
+  Dwfl_Process *process = dwfl->process;
+  if (process == NULL)
+    {
+      if (ebl_close)
+	ebl_closebackend (ebl);
+      __libdwfl_seterrno (DWFL_E_NOMEM);
+      return false;
+    }
+  process->ebl = ebl;
+  process->ebl_close = ebl_close;
+  process->pid = pid;
+  process->callbacks = thread_callbacks;
+  process->callbacks_arg = arg;
+  return true;
+}
+INTDEF(dwfl_attach_state)
+
+pid_t
+dwfl_pid (Dwfl *dwfl)
+{
+  if (dwfl->process == NULL)
+    {
+      __libdwfl_seterrno (DWFL_E_NO_ATTACH_STATE);
+      return -1;
+    }
+  return dwfl->process->pid;
+}
+INTDEF(dwfl_pid)
+
+Dwfl *
+dwfl_thread_dwfl (Dwfl_Thread *thread)
+{
+  return thread->process->dwfl;
+}
+INTDEF(dwfl_thread_dwfl)
+
+pid_t
+dwfl_thread_tid (Dwfl_Thread *thread)
+{
+  return thread->tid;
+}
+INTDEF(dwfl_thread_tid)
+
+Dwfl_Thread *
+dwfl_frame_thread (Dwfl_Frame *state)
+{
+  return state->thread;
+}
+INTDEF(dwfl_frame_thread)
+
+int
+dwfl_getthreads (Dwfl *dwfl, int (*callback) (Dwfl_Thread *thread, void *arg),
+		 void *arg)
+{
+  Dwfl_Process *process = dwfl->process;
+  if (process == NULL)
+    {
+      __libdwfl_seterrno (DWFL_E_NO_ATTACH_STATE);
+      return -1;
+    }
+
+  Dwfl_Thread thread;
+  thread.process = process;
+  thread.unwound = NULL;
+  thread.callbacks_arg = NULL;
+  for (;;)
+    {
+      thread.tid = process->callbacks->next_thread (dwfl,
+						    process->callbacks_arg,
+						    &thread.callbacks_arg);
+      if (thread.tid < 0)
+	{
+	  Dwfl_Error saved_errno = dwfl_errno ();
+	  thread_free_all_states (&thread);
+	  __libdwfl_seterrno (saved_errno);
+	  return -1;
+	}
+      if (thread.tid == 0)
+	{
+	  thread_free_all_states (&thread);
+	  __libdwfl_seterrno (DWFL_E_NOERROR);
+	  return 0;
+	}
+      int err = callback (&thread, arg);
+      if (err != DWARF_CB_OK)
+	{
+	  thread_free_all_states (&thread);
+	  return err;
+	}
+      assert (thread.unwound == NULL);
+    }
+  /* NOTREACHED */
+}
+INTDEF(dwfl_getthreads)
+
+int
+dwfl_thread_getframes (Dwfl_Thread *thread,
+		       int (*callback) (Dwfl_Frame *state, void *arg),
+		       void *arg)
+{
+  if (thread->unwound != NULL)
+    {
+      /* We had to be called from inside CALLBACK.  */
+      __libdwfl_seterrno (DWFL_E_ATTACH_STATE_CONFLICT);
+      return -1;
+    }
+  Ebl *ebl = thread->process->ebl;
+  if (ebl_frame_nregs (ebl) == 0)
+    {
+      __libdwfl_seterrno (DWFL_E_NO_UNWIND);
+      return -1;
+    }
+  if (state_alloc (thread) == NULL)
+    {
+      __libdwfl_seterrno (DWFL_E_NOMEM);
+      return -1;
+    }
+  Dwfl_Process *process = thread->process;
+  if (! process->callbacks->set_initial_registers (thread,
+						   thread->callbacks_arg))
+    {
+      thread_free_all_states (thread);
+      return -1;
+    }
+  if (! state_fetch_pc (thread->unwound))
+    {
+      if (process->callbacks->thread_detach)
+	process->callbacks->thread_detach (thread, thread->callbacks_arg);
+      thread_free_all_states (thread);
+      return -1;
+    }
+
+  Dwfl_Frame *state;
+  do
+    {
+      state = thread->unwound;
+      int err = callback (state, arg);
+      if (err != DWARF_CB_OK)
+	{
+	  if (process->callbacks->thread_detach)
+	    process->callbacks->thread_detach (thread, thread->callbacks_arg);
+	  thread_free_all_states (thread);
+	  return err;
+	}
+      __libdwfl_frame_unwind (state);
+      /* The old frame is no longer needed.  */
+      state_free (thread->unwound);
+      state = thread->unwound;
+    }
+  while (state && state->pc_state == DWFL_FRAME_STATE_PC_SET);
+
+  Dwfl_Error err = dwfl_errno ();
+  if (process->callbacks->thread_detach)
+    process->callbacks->thread_detach (thread, thread->callbacks_arg);
+  if (state == NULL || state->pc_state == DWFL_FRAME_STATE_ERROR)
+    {
+      thread_free_all_states (thread);
+      __libdwfl_seterrno (err);
+      return -1;
+    }
+  assert (state->pc_state == DWFL_FRAME_STATE_PC_UNDEFINED);
+  thread_free_all_states (thread);
+  return 0;
+}
+INTDEF(dwfl_thread_getframes)
diff --git a/libdwfl/dwfl_frame_pc.c b/libdwfl/dwfl_frame_pc.c
new file mode 100644
index 00000000..5462e4c7
--- /dev/null
+++ b/libdwfl/dwfl_frame_pc.c
@@ -0,0 +1,63 @@
+/* Get return address register value for frame.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "libdwflP.h"
+
+bool
+dwfl_frame_pc (Dwfl_Frame *state, Dwarf_Addr *pc, bool *isactivation)
+{
+  assert (state->pc_state == DWFL_FRAME_STATE_PC_SET);
+  *pc = state->pc;
+  if (isactivation)
+    {
+      /* Bottom frame?  */
+      if (state->initial_frame)
+	*isactivation = true;
+      /* *ISACTIVATION is logical union of whether current or previous frame
+	 state is SIGNAL_FRAME.  */
+      else if (state->signal_frame)
+	*isactivation = true;
+      else
+	{
+	  /* If the previous frame has unwound unsuccessfully just silently do
+	     not consider it could be a SIGNAL_FRAME.  */
+	  __libdwfl_frame_unwind (state);
+	  if (state->unwound == NULL
+	      || state->unwound->pc_state != DWFL_FRAME_STATE_PC_SET)
+	    *isactivation = false;
+	  else
+	    *isactivation = state->unwound->signal_frame;
+	}
+    }
+  return true;
+}
+INTDEF (dwfl_frame_pc)
diff --git a/libdwfl/dwfl_frame_regs.c b/libdwfl/dwfl_frame_regs.c
new file mode 100644
index 00000000..927bc15b
--- /dev/null
+++ b/libdwfl/dwfl_frame_regs.c
@@ -0,0 +1,57 @@
+/* Get Dwarf Frame state from modules present in DWFL.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#include "libdwflP.h"
+
+bool
+dwfl_thread_state_registers (Dwfl_Thread *thread, const int firstreg,
+			     unsigned nregs, const Dwarf_Word *regs)
+{
+  Dwfl_Frame *state = thread->unwound;
+  assert (state && state->unwound == NULL);
+  assert (state->initial_frame);
+  for (unsigned regno = firstreg; regno < firstreg + nregs; regno++)
+    if (! __libdwfl_frame_reg_set (state, regno, regs[regno - firstreg]))
+      {
+	__libdwfl_seterrno (DWFL_E_INVALID_REGISTER);
+	return false;
+      }
+  return true;
+}
+INTDEF(dwfl_thread_state_registers)
+
+void
+dwfl_thread_state_register_pc (Dwfl_Thread *thread, Dwarf_Word pc)
+{
+  Dwfl_Frame *state = thread->unwound;
+  assert (state && state->unwound == NULL);
+  assert (state->initial_frame);
+  state->pc = pc;
+  state->pc_state = DWFL_FRAME_STATE_PC_SET;
+}
+INTDEF(dwfl_thread_state_register_pc)
diff --git a/libdwfl/frame_unwind.c b/libdwfl/frame_unwind.c
new file mode 100644
index 00000000..1aed8cb5
--- /dev/null
+++ b/libdwfl/frame_unwind.c
@@ -0,0 +1,617 @@
+/* Get previous frame state for an existing frame state.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "cfi.h"
+#include <stdlib.h>
+#include "libdwflP.h"
+#include "../libdw/dwarf.h"
+#include <sys/ptrace.h>
+
+/* Maximum number of DWARF expression stack slots before returning an error.  */
+#define DWARF_EXPR_STACK_MAX 0x100
+
+/* Maximum number of DWARF expression executed operations before returning an
+   error.  */
+#define DWARF_EXPR_STEPS_MAX 0x1000
+
+#ifndef MAX
+# define MAX(a, b) ((a) > (b) ? (a) : (b))
+#endif
+
+bool
+internal_function
+__libdwfl_frame_reg_get (Dwfl_Frame *state, unsigned regno, Dwarf_Addr *val)
+{
+  Ebl *ebl = state->thread->process->ebl;
+  if (regno >= ebl_frame_nregs (ebl))
+    return false;
+  if ((state->regs_set[regno / sizeof (*state->regs_set) / 8]
+       & (1U << (regno % (sizeof (*state->regs_set) * 8)))) == 0)
+    return false;
+  if (val)
+    *val = state->regs[regno];
+  return true;
+}
+
+bool
+internal_function
+__libdwfl_frame_reg_set (Dwfl_Frame *state, unsigned regno, Dwarf_Addr val)
+{
+  Ebl *ebl = state->thread->process->ebl;
+  if (regno >= ebl_frame_nregs (ebl))
+    return false;
+  /* For example i386 user_regs_struct has signed fields.  */
+  if (ebl_get_elfclass (ebl) == ELFCLASS32)
+    val &= 0xffffffff;
+  state->regs_set[regno / sizeof (*state->regs_set) / 8] |=
+			      (1U << (regno % (sizeof (*state->regs_set) * 8)));
+  state->regs[regno] = val;
+  return true;
+}
+
+static bool
+state_get_reg (Dwfl_Frame *state, unsigned regno, Dwarf_Addr *val)
+{
+  if (! __libdwfl_frame_reg_get (state, regno, val))
+    {
+      __libdwfl_seterrno (DWFL_E_INVALID_REGISTER);
+      return false;
+    }
+  return true;
+}
+
+static int
+bra_compar (const void *key_voidp, const void *elem_voidp)
+{
+  Dwarf_Word offset = (uintptr_t) key_voidp;
+  const Dwarf_Op *op = elem_voidp;
+  return (offset > op->offset) - (offset < op->offset);
+}
+
+/* If FRAME is NULL is are computing CFI frame base.  In such case another
+   DW_OP_call_frame_cfa is no longer permitted.  */
+
+static bool
+expr_eval (Dwfl_Frame *state, Dwarf_Frame *frame, const Dwarf_Op *ops,
+	   size_t nops, Dwarf_Addr *result, Dwarf_Addr bias)
+{
+  Dwfl_Process *process = state->thread->process;
+  if (nops == 0)
+    {
+      __libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+      return false;
+    }
+  Dwarf_Addr *stack = NULL;
+  size_t stack_used = 0, stack_allocated = 0;
+
+  bool
+  push (Dwarf_Addr val)
+  {
+    if (stack_used >= DWARF_EXPR_STACK_MAX)
+      {
+	__libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+	return false;
+      }
+    if (stack_used == stack_allocated)
+      {
+	stack_allocated = MAX (stack_allocated * 2, 32);
+	Dwarf_Addr *stack_new = realloc (stack, stack_allocated * sizeof (*stack));
+	if (stack_new == NULL)
+	  {
+	    __libdwfl_seterrno (DWFL_E_NOMEM);
+	    return false;
+	  }
+	stack = stack_new;
+      }
+    stack[stack_used++] = val;
+    return true;
+  }
+
+  bool
+  pop (Dwarf_Addr *val)
+  {
+    if (stack_used == 0)
+      {
+	__libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+	return false;
+      }
+    *val = stack[--stack_used];
+    return true;
+  }
+
+  Dwarf_Addr val1, val2;
+  bool is_location = false;
+  size_t steps_count = 0;
+  for (const Dwarf_Op *op = ops; op < ops + nops; op++)
+    {
+      if (++steps_count > DWARF_EXPR_STEPS_MAX)
+	{
+	  __libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+	  return false;
+	}
+      switch (op->atom)
+      {
+	/* DW_OP_* order matches libgcc/unwind-dw2.c execute_stack_op:  */
+	case DW_OP_lit0 ... DW_OP_lit31:
+	  if (! push (op->atom - DW_OP_lit0))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_addr:
+	  if (! push (op->number + bias))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_GNU_encoded_addr:
+	  /* Missing support in the rest of elfutils.  */
+	  __libdwfl_seterrno (DWFL_E_UNSUPPORTED_DWARF);
+	  return false;
+	case DW_OP_const1u:
+	case DW_OP_const1s:
+	case DW_OP_const2u:
+	case DW_OP_const2s:
+	case DW_OP_const4u:
+	case DW_OP_const4s:
+	case DW_OP_const8u:
+	case DW_OP_const8s:
+	case DW_OP_constu:
+	case DW_OP_consts:
+	  if (! push (op->number))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_reg0 ... DW_OP_reg31:
+	  if (! state_get_reg (state, op->atom - DW_OP_reg0, &val1)
+	      || ! push (val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_regx:
+	  if (! state_get_reg (state, op->number, &val1) || ! push (val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_breg0 ... DW_OP_breg31:
+	  if (! state_get_reg (state, op->atom - DW_OP_breg0, &val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  val1 += op->number;
+	  if (! push (val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_bregx:
+	  if (! state_get_reg (state, op->number, &val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  val1 += op->number2;
+	  if (! push (val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_dup:
+	  if (! pop (&val1) || ! push (val1) || ! push (val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_drop:
+	  if (! pop (&val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_pick:
+	  if (stack_used <= op->number)
+	    {
+	      free (stack);
+	      __libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+	      return false;
+	    }
+	  if (! push (stack[stack_used - 1 - op->number]))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_over:
+	  if (! pop (&val1) || ! pop (&val2)
+	      || ! push (val2) || ! push (val1) || ! push (val2))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_swap:
+	  if (! pop (&val1) || ! pop (&val2) || ! push (val1) || ! push (val2))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	case DW_OP_rot:
+	  {
+	    Dwarf_Addr val3;
+	    if (! pop (&val1) || ! pop (&val2) || ! pop (&val3)
+		|| ! push (val1) || ! push (val3) || ! push (val2))
+	      {
+		free (stack);
+		return false;
+	      }
+	  }
+	  break;
+	case DW_OP_deref:
+	case DW_OP_deref_size:
+	  if (process->callbacks->memory_read == NULL)
+	    {
+	      free (stack);
+	      __libdwfl_seterrno (DWFL_E_INVALID_ARGUMENT);
+	      return false;
+	    }
+	  if (! pop (&val1)
+	      || ! process->callbacks->memory_read (process->dwfl, val1, &val1,
+						    process->callbacks_arg))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  if (op->atom == DW_OP_deref_size)
+	    {
+	      const int elfclass = frame->cache->e_ident[EI_CLASS];
+	      const unsigned addr_bytes = elfclass == ELFCLASS32 ? 4 : 8;
+	      if (op->number > addr_bytes)
+		{
+		  free (stack);
+		  __libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+		  return false;
+		}
+#if BYTE_ORDER == BIG_ENDIAN
+	      if (op->number == 0)
+		val1 = 0;
+	      else
+		val1 >>= (addr_bytes - op->number) * 8;
+#else
+	      if (op->number < 8)
+		val1 &= (1 << (op->number * 8)) - 1;
+#endif
+	    }
+	  if (! push (val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+#define UNOP(atom, expr)						\
+	case atom:							\
+	  if (! pop (&val1) || ! push (expr))				\
+	    {								\
+	      free (stack);						\
+	      return false;						\
+	    }								\
+	  break;
+	UNOP (DW_OP_abs, abs ((int64_t) val1))
+	UNOP (DW_OP_neg, -(int64_t) val1)
+	UNOP (DW_OP_not, ~val1)
+#undef UNOP
+	case DW_OP_plus_uconst:
+	  if (! pop (&val1) || ! push (val1 + op->number))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+#define BINOP(atom, op)							\
+	case atom:							\
+	  if (! pop (&val2) || ! pop (&val1) || ! push (val1 op val2))	\
+	    {								\
+	      free (stack);						\
+	      return false;						\
+	    }								\
+	  break;
+#define BINOP_SIGNED(atom, op)						\
+	case atom:							\
+	  if (! pop (&val2) || ! pop (&val1)				\
+	      || ! push ((int64_t) val1 op (int64_t) val2))		\
+	    {								\
+	      free (stack);						\
+	      return false;						\
+	    }								\
+	  break;
+	BINOP (DW_OP_and, &)
+	case DW_OP_div:
+	  if (! pop (&val2) || ! pop (&val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  if (val2 == 0)
+	    {
+	      free (stack);
+	      __libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+	      return false;
+	    }
+	  if (! push ((int64_t) val1 / (int64_t) val2))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	BINOP (DW_OP_minus, -)
+	case DW_OP_mod:
+	  if (! pop (&val2) || ! pop (&val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  if (val2 == 0)
+	    {
+	      free (stack);
+	      __libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+	      return false;
+	    }
+	  if (! push (val1 % val2))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  break;
+	BINOP (DW_OP_mul, *)
+	BINOP (DW_OP_or, |)
+	BINOP (DW_OP_plus, +)
+	BINOP (DW_OP_shl, <<)
+	BINOP (DW_OP_shr, >>)
+	BINOP_SIGNED (DW_OP_shra, >>)
+	BINOP (DW_OP_xor, ^)
+	BINOP_SIGNED (DW_OP_le, <=)
+	BINOP_SIGNED (DW_OP_ge, >=)
+	BINOP_SIGNED (DW_OP_eq, ==)
+	BINOP_SIGNED (DW_OP_lt, <)
+	BINOP_SIGNED (DW_OP_gt, >)
+	BINOP_SIGNED (DW_OP_ne, !=)
+#undef BINOP
+#undef BINOP_SIGNED
+	case DW_OP_bra:
+	  if (! pop (&val1))
+	    {
+	      free (stack);
+	      return false;
+	    }
+	  if (val1 == 0)
+	    break;
+	  /* FALLTHRU */
+	case DW_OP_skip:;
+	  Dwarf_Word offset = op->offset + 1 + 2 + (int16_t) op->number;
+	  const Dwarf_Op *found = bsearch ((void *) (uintptr_t) offset, ops, nops,
+					   sizeof (*ops), bra_compar);
+	  if (found == NULL)
+	    {
+	      free (stack);
+	      /* PPC32 vDSO has such invalid operations.  */
+	      __libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+	      return false;
+	    }
+	  /* Undo the 'for' statement increment.  */
+	  op = found - 1;
+	  break;
+	case DW_OP_nop:
+	  break;
+	/* DW_OP_* not listed in libgcc/unwind-dw2.c execute_stack_op:  */
+	case DW_OP_call_frame_cfa:;
+	  // Not used by CFI itself but it is synthetized by elfutils internation.
+	  Dwarf_Op *cfa_ops;
+	  size_t cfa_nops;
+	  Dwarf_Addr cfa;
+	  if (frame == NULL
+	      || dwarf_frame_cfa (frame, &cfa_ops, &cfa_nops) != 0
+	      || ! expr_eval (state, NULL, cfa_ops, cfa_nops, &cfa, bias)
+	      || ! push (cfa))
+	    {
+	      __libdwfl_seterrno (DWFL_E_LIBDW);
+	      free (stack);
+	      return false;
+	    }
+	  is_location = true;
+	  break;
+	case DW_OP_stack_value:
+	  // Not used by CFI itself but it is synthetized by elfutils internation.
+	  is_location = false;
+	  break;
+	default:
+	  __libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+	  return false;
+      }
+    }
+  if (! pop (result))
+    {
+      free (stack);
+      return false;
+    }
+  free (stack);
+  if (is_location)
+    {
+      if (process->callbacks->memory_read == NULL)
+	{
+	  __libdwfl_seterrno (DWFL_E_INVALID_ARGUMENT);
+	  return false;
+	}
+      if (! process->callbacks->memory_read (process->dwfl, *result, result,
+					     process->callbacks_arg))
+	return false;
+    }
+  return true;
+}
+
+/* The logic is to call __libdwfl_seterrno for any CFI bytecode interpretation
+   error so one can easily catch the problem with a debugger.  Still there are
+   archs with invalid CFI for some registers where the registers are never used
+   later.  Therefore we continue unwinding leaving the registers undefined.  */
+
+static void
+handle_cfi (Dwfl_Frame *state, Dwarf_Addr pc, Dwarf_CFI *cfi, Dwarf_Addr bias)
+{
+  Dwarf_Frame *frame;
+  if (INTUSE(dwarf_cfi_addrframe) (cfi, pc, &frame) != 0)
+    {
+      __libdwfl_seterrno (DWFL_E_LIBDW);
+      return;
+    }
+  Dwfl_Thread *thread = state->thread;
+  Dwfl_Process *process = thread->process;
+  Ebl *ebl = process->ebl;
+  size_t nregs = ebl_frame_nregs (ebl);
+  assert (nregs > 0);
+  Dwfl_Frame *unwound;
+  unwound = malloc (sizeof (*unwound) + sizeof (*unwound->regs) * nregs);
+  state->unwound = unwound;
+  unwound->thread = thread;
+  unwound->unwound = NULL;
+  unwound->signal_frame = frame->fde->cie->signal_frame;
+  unwound->initial_frame = false;
+  unwound->pc_state = DWFL_FRAME_STATE_ERROR;
+  memset (unwound->regs_set, 0, sizeof (unwound->regs_set));
+  for (unsigned regno = 0; regno < nregs; regno++)
+    {
+      Dwarf_Op reg_ops_mem[3], *reg_ops;
+      size_t reg_nops;
+      if (dwarf_frame_register (frame, regno, reg_ops_mem, &reg_ops,
+				&reg_nops) != 0)
+	{
+	  __libdwfl_seterrno (DWFL_E_LIBDW);
+	  continue;
+	}
+      Dwarf_Addr regval;
+      if (reg_nops == 0)
+	{
+	  if (reg_ops == reg_ops_mem)
+	    {
+	      /* REGNO is undefined.  */
+	      unsigned ra = frame->fde->cie->return_address_register;
+	      if (regno == ra)
+		unwound->pc_state = DWFL_FRAME_STATE_PC_UNDEFINED;
+	      continue;
+	    }
+	  else if (reg_ops == NULL)
+	    {
+	      /* REGNO is same-value.  */
+	      if (! state_get_reg (state, regno, &regval))
+		continue;
+	    }
+	  else
+	    {
+	      __libdwfl_seterrno (DWFL_E_INVALID_DWARF);
+	      continue;
+	    }
+	}
+      else if (! expr_eval (state, frame, reg_ops, reg_nops, &regval, bias))
+	{
+	  /* PPC32 vDSO has various invalid operations, ignore them.  The
+	     register will look as unset causing an error later, if used.
+	     But PPC32 does not use such registers.  */
+	  continue;
+	}
+      if (! __libdwfl_frame_reg_set (unwound, regno, regval))
+	{
+	  __libdwfl_seterrno (DWFL_E_INVALID_REGISTER);
+	  continue;
+	}
+    }
+  if (unwound->pc_state == DWFL_FRAME_STATE_ERROR
+      && __libdwfl_frame_reg_get (unwound,
+				  frame->fde->cie->return_address_register,
+				  &unwound->pc))
+    {
+      /* PPC32 __libc_start_main properly CFI-unwinds PC as zero.  Currently
+	 none of the archs supported for unwinding have zero as a valid PC.  */
+      if (unwound->pc == 0)
+	unwound->pc_state = DWFL_FRAME_STATE_PC_UNDEFINED;
+      else
+	unwound->pc_state = DWFL_FRAME_STATE_PC_SET;
+    }
+}
+
+void
+internal_function
+__libdwfl_frame_unwind (Dwfl_Frame *state)
+{
+  if (state->unwound)
+    return;
+  /* Do not ask dwfl_frame_pc for ISACTIVATION, it would try to unwind STATE
+     which would deadlock us.  */
+  Dwarf_Addr pc;
+  bool ok = INTUSE(dwfl_frame_pc) (state, &pc, NULL);
+  assert (ok);
+  /* Check whether this is the initial frame or a signal frame.
+     Then we need to unwind from the original, unadjusted PC.  */
+  if (! state->initial_frame && ! state->signal_frame)
+    pc--;
+  Dwfl_Module *mod = INTUSE(dwfl_addrmodule) (state->thread->process->dwfl, pc);
+  if (mod == NULL)
+    __libdwfl_seterrno (DWFL_E_NO_DWARF);
+  else
+    {
+      Dwarf_Addr bias;
+      Dwarf_CFI *cfi_eh = INTUSE(dwfl_module_eh_cfi) (mod, &bias);
+      if (cfi_eh)
+	{
+	  handle_cfi (state, pc - bias, cfi_eh, bias);
+	  if (state->unwound)
+	    return;
+	}
+      Dwarf_CFI *cfi_dwarf = INTUSE(dwfl_module_dwarf_cfi) (mod, &bias);
+      if (cfi_dwarf)
+	{
+	  handle_cfi (state, pc - bias, cfi_dwarf, bias);
+	  if (state->unwound)
+	    return;
+	}
+    }
+}
diff --git a/libdwfl/libdwfl.h b/libdwfl/libdwfl.h
index 2ba82343..bbabb708 100644
--- a/libdwfl/libdwfl.h
+++ b/libdwfl/libdwfl.h
@@ -1,5 +1,5 @@
 /* Interfaces for libdwfl.
-   Copyright (C) 2005-2010 Red Hat, Inc.
+   Copyright (C) 2005-2010, 2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -41,6 +41,14 @@ typedef struct Dwfl_Module Dwfl_Module;
 /* Handle describing a line record.  */
 typedef struct Dwfl_Line Dwfl_Line;
 
+/* This holds information common for all the frames of one backtrace for
+   a partical thread/task/TID.  Several threads belong to one Dwfl.  */
+typedef struct Dwfl_Thread Dwfl_Thread;
+
+/* This holds everything we know about the state of the frame at a particular
+   PC location described by an FDE belonging to Dwfl_Thread.  */
+typedef struct Dwfl_Frame Dwfl_Frame;
+
 /* Callbacks.  */
 typedef struct
 {
@@ -353,11 +361,14 @@ extern int dwfl_linux_kernel_report_offline (Dwfl *dwfl, const char *release,
    supply non-NULL EXECUTABLE, otherwise dynamic libraries will not be loaded
    into the DWFL map.  This might call dwfl_report_elf on file names found in
    the dump if reading some link_map files is the only way to ascertain those
-   modules' addresses.
+   modules' addresses.  dwfl_attach_state is also called for DWFL,
+   dwfl_core_file_report does not fail if the dwfl_attach_state call has failed.
    Returns the number of modules reported, or -1 for errors.  */
 extern int dwfl_core_file_report (Dwfl *dwfl, Elf *elf, const char *executable);
 
 /* Call dwfl_report_module for each file mapped into the address space of PID.
+   dwfl_attach_state is also called for DWFL, dwfl_linux_proc_report does
+   not fail if the dwfl_attach_state call has failed.
    Returns zero on success, -1 if dwfl_report_module failed,
    or an errno code if opening the kernel binary failed.  */
 extern int dwfl_linux_proc_report (Dwfl *dwfl, pid_t pid);
@@ -567,6 +578,128 @@ extern Dwarf_CFI *dwfl_module_dwarf_cfi (Dwfl_Module *mod, Dwarf_Addr *bias);
 extern Dwarf_CFI *dwfl_module_eh_cfi (Dwfl_Module *mod, Dwarf_Addr *bias);
 
 
+typedef struct
+{
+  /* Called to iterate through threads.  Returns next TID (thread ID) on
+     success, a negative number on failure and zero if there are no more
+     threads.  dwfl_errno () should be set if negative number has been
+     returned.  *THREAD_ARGP is NULL on first call, and may be optionally
+     set by the implementation. The value set by the implementation will
+     be passed in on the next call to NEXT_THREAD.  THREAD_ARGP is never
+     NULL.  *THREAD_ARGP will be passed to set_initial_registers or
+     thread_detach callbacks together with Dwfl_Thread *thread.  This
+     method must not be NULL.  */
+  pid_t (*next_thread) (Dwfl *dwfl, void *dwfl_arg, void **thread_argp)
+    __nonnull_attribute__ (1);
+
+  /* Called during unwinding to access memory (stack) state.  Returns true for
+     successfully read *RESULT or false and sets dwfl_errno () on failure.
+     This method may be NULL - in such case dwfl_thread_getframes will return
+     only the initial frame.  */
+  bool (*memory_read) (Dwfl *dwfl, Dwarf_Addr addr, Dwarf_Word *result,
+                       void *dwfl_arg)
+    __nonnull_attribute__ (1, 3);
+
+  /* Called on initial unwind to get the initial register state of the first
+     frame.  Should call dwfl_thread_state_registers, possibly multiple times
+     for different ranges and possibly also dwfl_thread_state_register_pc, to
+     fill in initial (DWARF) register values.  After this call, till at least
+     thread_detach is called, the thread is assumed to be frozen, so that it is
+     safe to unwind.  Returns true on success or false and sets dwfl_errno ()
+     on failure.  In the case of a failure thread_detach will not be called.
+     This method must not be NULL.  */
+  bool (*set_initial_registers) (Dwfl_Thread *thread, void *thread_arg)
+    __nonnull_attribute__ (1);
+
+  /* Called by dwfl_end.  All thread_detach method calls have been already
+     done.  This method may be NULL.  */
+  void (*detach) (Dwfl *dwfl, void *dwfl_arg)
+    __nonnull_attribute__ (1);
+
+  /* Called when unwinding is done.  No callback will be called after
+     this method has been called.  Iff set_initial_registers was called for
+     a TID and it returned success thread_detach will be called before the
+     detach method above.  This method may be NULL.  */
+  void (*thread_detach) (Dwfl_Thread *thread, void *thread_arg)
+    __nonnull_attribute__ (1);
+} Dwfl_Thread_Callbacks;
+
+/* PID is the process id associated with the DWFL state.  Architecture of DWFL
+   modules is specified by MACHINE.  Use EM_NONE to detect architecture from
+   DWFL.  If EBL is NULL the function will detect it from arbitrary Dwfl_Module
+   of DWFL.  DWFL_ARG is the callback backend state.  DWFL_ARG will be provided
+   to the callbacks.  *THREAD_CALLBACKS function pointers must remain valid
+   during lifetime of DWFL.  Function returns true on success,
+   false otherwise.  */
+bool dwfl_attach_state (Dwfl *dwfl, int machine, pid_t pid,
+                        const Dwfl_Thread_Callbacks *thread_callbacks,
+			void *dwfl_arg)
+  __nonnull_attribute__ (1, 4);
+
+/* Return PID for the process associated with DWFL.  Function returns -1 if
+   dwfl_attach_state was not called for DWFL.  */
+pid_t dwfl_pid (Dwfl *dwfl)
+  __nonnull_attribute__ (1);
+
+/* Return DWFL from which THREAD was created using dwfl_getthreads.  */
+Dwfl *dwfl_thread_dwfl (Dwfl_Thread *thread)
+  __nonnull_attribute__ (1);
+
+/* Return positive TID (thread ID) for THREAD.  This function never fails.  */
+pid_t dwfl_thread_tid (Dwfl_Thread *thread)
+  __nonnull_attribute__ (1);
+
+/* Return thread for frame STATE.  This function never fails.  */
+Dwfl_Thread *dwfl_frame_thread (Dwfl_Frame *state)
+  __nonnull_attribute__ (1);
+
+/* Called by Dwfl_Thread_Callbacks.set_initial_registers implementation.
+   For every known continuous block of registers <FIRSTREG..FIRSTREG+NREGS)
+   (inclusive..exclusive) set their content to REGS (array of NREGS items).
+   Function returns false if any of the registers has invalid number.  */
+bool dwfl_thread_state_registers (Dwfl_Thread *thread, const int firstreg,
+                                  unsigned nregs, const Dwarf_Word *regs)
+  __nonnull_attribute__ (1, 4);
+
+/* Called by Dwfl_Thread_Callbacks.set_initial_registers implementation.
+   If PC is not contained among DWARF registers passed by
+   dwfl_thread_state_registers on the target architecture pass the PC value
+   here.  */
+void dwfl_thread_state_register_pc (Dwfl_Thread *thread, Dwarf_Word pc)
+  __nonnull_attribute__ (1);
+
+/* Iterate through the threads for a process.  Returns zero if all threads have
+   been processed by the callback, returns -1 on error, or the value of the
+   callback when not DWARF_CB_OK.  -1 returned on error will set dwfl_errno ().
+   Keeps calling the callback with the next thread while the callback returns
+   DWARF_CB_OK, till there are no more threads.  */
+int dwfl_getthreads (Dwfl *dwfl,
+		     int (*callback) (Dwfl_Thread *thread, void *arg),
+		     void *arg)
+  __nonnull_attribute__ (1, 2);
+
+/* Iterate through the frames for a thread.  Returns zero if all frames
+   have been processed by the callback, returns -1 on error, or the value of
+   the callback when not DWARF_CB_OK.  -1 returned on error will
+   set dwfl_errno ().  Some systems return error instead of zero on end of the
+   backtrace, for cross-platform compatibility callers should consider error as
+   a zero.  Keeps calling the callback with the next frame while the callback
+   returns DWARF_CB_OK, till there are no more frames.  On start will call the
+   set_initial_registers callback and on return will call the detach_thread
+   callback of the Dwfl_Thread.  */
+int dwfl_thread_getframes (Dwfl_Thread *thread,
+			   int (*callback) (Dwfl_Frame *state, void *arg),
+			   void *arg)
+  __nonnull_attribute__ (1, 2);
+
+/* Return *PC (program counter) for thread-specific frame STATE.
+   Set *ISACTIVATION according to DWARF frame "activation" definition.
+   Typically you need to substract 1 from *PC if *ACTIVATION is false to safely
+   find function of the caller.  ACTIVATION may be NULL.  PC must not be NULL.
+   Function returns false if it failed to find *PC.  */
+bool dwfl_frame_pc (Dwfl_Frame *state, Dwarf_Addr *pc, bool *isactivation)
+  __nonnull_attribute__ (1, 2);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/libdwfl/libdwflP.h b/libdwfl/libdwflP.h
index 7e46478d..ff488132 100644
--- a/libdwfl/libdwflP.h
+++ b/libdwfl/libdwflP.h
@@ -1,5 +1,5 @@
 /* Internal definitions for libdwfl.
-   Copyright (C) 2005-2012 Red Hat, Inc.
+   Copyright (C) 2005-2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -42,6 +42,8 @@
 
 #include "../libdw/libdwP.h"	/* We need its INTDECLs.  */
 
+typedef struct Dwfl_Process Dwfl_Process;
+
 /* gettext helper macros.  */
 #define _(Str) dgettext ("elfutils", Str)
 
@@ -74,7 +76,20 @@
   DWFL_ERROR (BADELF, N_("not a valid ELF file"))			      \
   DWFL_ERROR (WEIRD_TYPE, N_("cannot handle DWARF type description"))	      \
   DWFL_ERROR (WRONG_ID_ELF, N_("ELF file does not match build ID"))	      \
-  DWFL_ERROR (BAD_PRELINK, N_("corrupt .gnu.prelink_undo section data"))
+  DWFL_ERROR (BAD_PRELINK, N_("corrupt .gnu.prelink_undo section data"))      \
+  DWFL_ERROR (LIBEBL_BAD, N_("Internal error due to ebl"))		      \
+  DWFL_ERROR (CORE_MISSING, N_("Missing data in core file"))		      \
+  DWFL_ERROR (INVALID_REGISTER, N_("Invalid register"))			      \
+  DWFL_ERROR (PROCESS_MEMORY_READ, N_("Error reading process memory"))	      \
+  DWFL_ERROR (PROCESS_NO_ARCH, N_("Couldn't find architecture of any ELF"))   \
+  DWFL_ERROR (PARSE_PROC, N_("Error parsing /proc filesystem"))		      \
+  DWFL_ERROR (INVALID_DWARF, N_("Invalid DWARF"))			      \
+  DWFL_ERROR (UNSUPPORTED_DWARF, N_("Unsupported DWARF"))		      \
+  DWFL_ERROR (NEXT_THREAD_FAIL, N_("Unable to find more threads"))	      \
+  DWFL_ERROR (ATTACH_STATE_CONFLICT, N_("Dwfl already has attached state"))   \
+  DWFL_ERROR (NO_ATTACH_STATE, N_("Dwfl has no attached state"))	      \
+  DWFL_ERROR (NO_UNWIND, N_("Unwinding not supported for this architecture")) \
+  DWFL_ERROR (INVALID_ARGUMENT, N_("Invalid argument"))
 
 #define DWFL_ERROR(name, text) DWFL_E_##name,
 typedef enum { DWFL_ERRORS DWFL_E_NUM } Dwfl_Error;
@@ -92,6 +107,8 @@ struct Dwfl
 
   Dwfl_Module *modulelist;    /* List in order used by full traversals.  */
 
+  Dwfl_Process *process;
+
   GElf_Addr offline_next_address;
 
   GElf_Addr segment_align;	/* Smallest granularity of segments.  */
@@ -189,7 +206,72 @@ struct Dwfl_Module
   bool gc;			/* Mark/sweep flag.  */
 };
 
+/* This holds information common for all the threads/tasks/TIDs of one process
+   for backtraces.  */
+
+struct Dwfl_Process
+{
+  struct Dwfl *dwfl;
+  pid_t pid;
+  const Dwfl_Thread_Callbacks *callbacks;
+  void *callbacks_arg;
+  struct ebl *ebl;
+  bool ebl_close:1;
+};
+
+/* See its typedef in libdwfl.h.  */
+
+struct Dwfl_Thread
+{
+  Dwfl_Process *process;
+  pid_t tid;
+  /* The current frame being unwound.  Initially it is the bottom frame.
+     Later the processed frames get freed and this pointer is updated.  */
+  Dwfl_Frame *unwound;
+  void *callbacks_arg;
+};
+
+/* See its typedef in libdwfl.h.  */
+
+struct Dwfl_Frame
+{
+  Dwfl_Thread *thread;
+  /* Previous (outer) frame.  */
+  Dwfl_Frame *unwound;
+  bool signal_frame : 1;
+  bool initial_frame : 1;
+  enum
+  {
+    /* This structure is still being initialized or there was an error
+       initializing it.  */
+    DWFL_FRAME_STATE_ERROR,
+    /* PC field is valid.  */
+    DWFL_FRAME_STATE_PC_SET,
+    /* PC field is undefined, this means the next (inner) frame was the
+       outermost frame.  */
+    DWFL_FRAME_STATE_PC_UNDEFINED
+  } pc_state;
+  /* Either initialized from appropriate REGS element or on some archs
+     initialized separately as the return address has no DWARF register.  */
+  Dwarf_Addr pc;
+  /* (1 << X) bitmask where 0 <= X < ebl_frame_nregs.  */
+  uint64_t regs_set[3];
+  /* REGS array size is ebl_frame_nregs.
+     REGS_SET tells which of the REGS are valid.  */
+  Dwarf_Addr regs[];
+};
+
+/* Fetch value from Dwfl_Frame->regs indexed by DWARF REGNO.
+   No error code is set if the function returns FALSE.  */
+bool __libdwfl_frame_reg_get (Dwfl_Frame *state, unsigned regno,
+			      Dwarf_Addr *val)
+  internal_function;
 
+/* Store value to Dwfl_Frame->regs indexed by DWARF REGNO.
+   No error code is set if the function returns FALSE.  */
+bool __libdwfl_frame_reg_set (Dwfl_Frame *state, unsigned regno,
+			      Dwarf_Addr val)
+  internal_function;
 
 /* Information cached about each CU in Dwfl_Module.dw.  */
 struct dwfl_cu
@@ -415,6 +497,33 @@ extern Dwfl_Module *__libdwfl_report_offline (Dwfl *dwfl, const char *name,
 								const char *))
   internal_function;
 
+/* Free PROCESS.  Unlink and free also any structures it references.  */
+extern void __libdwfl_process_free (Dwfl_Process *process)
+  internal_function;
+
+/* Update STATE->unwound for the unwound frame.
+   On error STATE->unwound == NULL
+   or STATE->unwound->pc_state == DWFL_FRAME_STATE_ERROR;
+   in such case dwfl_errno () is set.
+   If STATE->unwound->pc_state == DWFL_FRAME_STATE_PC_UNDEFINED
+   then STATE was the last valid frame.  */
+extern void __libdwfl_frame_unwind (Dwfl_Frame *state)
+  internal_function;
+
+/* Call dwfl_attach_state for PID, return true if successful.  */
+extern bool __libdwfl_attach_state_for_pid (Dwfl *dwfl, pid_t pid)
+  internal_function;
+
+/* Call dwfl_attach_state for CORE, return true if successful.  */
+extern bool __libdwfl_attach_state_for_core (Dwfl *dwfl, Elf *core)
+  internal_function;
+
+/* Align segment START downwards or END upwards addresses according to DWFL.  */
+extern GElf_Addr __libdwfl_segment_start (Dwfl *dwfl, GElf_Addr start)
+  internal_function;
+extern GElf_Addr __libdwfl_segment_end (Dwfl *dwfl, GElf_Addr end)
+  internal_function;
+
 /* Decompression wrappers: decompress whole file into memory.  */
 extern Dwfl_Error __libdw_gunzip  (int fd, off64_t start_offset,
 				   void *mapped, size_t mapped_size,
@@ -557,6 +666,16 @@ INTDECL (dwfl_offline_section_address)
 INTDECL (dwfl_module_relocate_address)
 INTDECL (dwfl_module_dwarf_cfi)
 INTDECL (dwfl_module_eh_cfi)
+INTDECL (dwfl_attach_state)
+INTDECL (dwfl_pid)
+INTDECL (dwfl_thread_dwfl)
+INTDECL (dwfl_thread_tid)
+INTDECL (dwfl_frame_thread)
+INTDECL (dwfl_thread_state_registers)
+INTDECL (dwfl_thread_state_register_pc)
+INTDECL (dwfl_getthreads)
+INTDECL (dwfl_thread_getframes)
+INTDECL (dwfl_frame_pc)
 
 /* Leading arguments standard to callbacks passed a Dwfl_Module.  */
 #define MODCB_ARGS(mod)	(mod), &(mod)->userdata, (mod)->name, (mod)->low_addr
diff --git a/libdwfl/linux-core-attach.c b/libdwfl/linux-core-attach.c
new file mode 100644
index 00000000..106d7649
--- /dev/null
+++ b/libdwfl/linux-core-attach.c
@@ -0,0 +1,380 @@
+/* Get Dwarf Frame state for target core file.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#include "libdwflP.h"
+#include <fcntl.h>
+#include "system.h"
+
+#ifndef MIN
+# define MIN(a, b) ((a) < (b) ? (a) : (b))
+#endif
+
+struct core_arg
+{
+  Elf *core;
+  Elf_Data *note_data;
+  size_t thread_note_offset;
+  Ebl *ebl;
+};
+
+struct thread_arg
+{
+  struct core_arg *core_arg;
+  size_t note_offset;
+};
+
+static bool
+core_memory_read (Dwfl *dwfl, Dwarf_Addr addr, Dwarf_Word *result,
+		  void *dwfl_arg)
+{
+  Dwfl_Process *process = dwfl->process;
+  struct core_arg *core_arg = dwfl_arg;
+  Elf *core = core_arg->core;
+  assert (core != NULL);
+  static size_t phnum;
+  if (elf_getphdrnum (core, &phnum) < 0)
+    {
+      __libdwfl_seterrno (DWFL_E_LIBELF);
+      return false;
+    }
+  for (size_t cnt = 0; cnt < phnum; ++cnt)
+    {
+      GElf_Phdr phdr_mem, *phdr = gelf_getphdr (core, cnt, &phdr_mem);
+      if (phdr == NULL || phdr->p_type != PT_LOAD)
+	continue;
+      /* Bias is zero here, a core file itself has no bias.  */
+      GElf_Addr start = __libdwfl_segment_start (dwfl, phdr->p_vaddr);
+      GElf_Addr end = __libdwfl_segment_end (dwfl,
+					     phdr->p_vaddr + phdr->p_memsz);
+      unsigned bytes = ebl_get_elfclass (process->ebl) == ELFCLASS64 ? 8 : 4;
+      if (addr < start || addr + bytes > end)
+	continue;
+      Elf_Data *data;
+      data = elf_getdata_rawchunk (core, phdr->p_offset + addr - start,
+				   bytes, ELF_T_ADDR);
+      if (data == NULL)
+	{
+	  __libdwfl_seterrno (DWFL_E_LIBELF);
+	  return false;
+	}
+      assert (data->d_size == bytes);
+      /* FIXME: Currently any arch supported for unwinding supports
+	 unaligned access.  */
+      if (bytes == 8)
+	*result = *(const uint64_t *) data->d_buf;
+      else
+	*result = *(const uint32_t *) data->d_buf;
+      return true;
+    }
+  __libdwfl_seterrno (DWFL_E_ADDR_OUTOFRANGE);
+  return false;
+}
+
+static pid_t
+core_next_thread (Dwfl *dwfl __attribute__ ((unused)), void *dwfl_arg,
+		  void **thread_argp)
+{
+  struct core_arg *core_arg = dwfl_arg;
+  Elf *core = core_arg->core;
+  GElf_Nhdr nhdr;
+  size_t name_offset;
+  size_t desc_offset;
+  Elf_Data *note_data = core_arg->note_data;
+  size_t offset;
+  while (offset = core_arg->thread_note_offset, offset < note_data->d_size
+	 && (core_arg->thread_note_offset = gelf_getnote (note_data, offset,
+							  &nhdr, &name_offset,
+							  &desc_offset)) > 0)
+    {
+      /* Do not check NAME for now, help broken Linux kernels.  */
+      const char *name = note_data->d_buf + name_offset;
+      const char *desc = note_data->d_buf + desc_offset;
+      GElf_Word regs_offset;
+      size_t nregloc;
+      const Ebl_Register_Location *reglocs;
+      size_t nitems;
+      const Ebl_Core_Item *items;
+      if (! ebl_core_note (core_arg->ebl, &nhdr, name,
+			   &regs_offset, &nregloc, &reglocs, &nitems, &items))
+	{
+	  /* This note may be just not recognized, skip it.  */
+	  continue;
+	}
+      if (nhdr.n_type != NT_PRSTATUS)
+	continue;
+      const Ebl_Core_Item *item;
+      for (item = items; item < items + nitems; item++)
+	if (strcmp (item->name, "pid") == 0)
+	  break;
+      if (item == items + nitems)
+	continue;
+      uint32_t val32 = *(const uint32_t *) (desc + item->offset);
+      val32 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
+		? be32toh (val32) : le32toh (val32));
+      pid_t tid = (int32_t) val32;
+      eu_static_assert (sizeof val32 <= sizeof tid);
+      struct thread_arg *thread_arg = malloc (sizeof (*thread_arg));
+      if (thread_arg == NULL)
+	{
+	  __libdwfl_seterrno (DWFL_E_NOMEM);
+	  return -1;
+	}
+      thread_arg->core_arg = core_arg;
+      thread_arg->note_offset = offset;
+      *thread_argp = thread_arg;
+      return tid;
+    }
+  return 0;
+}
+
+static bool
+core_set_initial_registers (Dwfl_Thread *thread, void *thread_arg_voidp)
+{
+  struct thread_arg *thread_arg = thread_arg_voidp;
+  struct core_arg *core_arg = thread_arg->core_arg;
+  Elf *core = core_arg->core;
+  size_t offset = thread_arg->note_offset;
+  GElf_Nhdr nhdr;
+  size_t name_offset;
+  size_t desc_offset;
+  Elf_Data *note_data = core_arg->note_data;
+  size_t nregs = ebl_frame_nregs (core_arg->ebl);
+  assert (nregs > 0);
+  assert (offset < note_data->d_size);
+  size_t getnote_err = gelf_getnote (note_data, offset, &nhdr, &name_offset,
+				     &desc_offset);
+  /* __libdwfl_attach_state_for_core already verified the note is there.  */
+  assert (getnote_err != 0);
+  /* Do not check NAME for now, help broken Linux kernels.  */
+  const char *name = note_data->d_buf + name_offset;
+  const char *desc = note_data->d_buf + desc_offset;
+  GElf_Word regs_offset;
+  size_t nregloc;
+  const Ebl_Register_Location *reglocs;
+  size_t nitems;
+  const Ebl_Core_Item *items;
+  int core_note_err = ebl_core_note (core_arg->ebl, &nhdr, name, &regs_offset,
+				     &nregloc, &reglocs, &nitems, &items);
+  /* __libdwfl_attach_state_for_core already verified the note is there.  */
+  assert (core_note_err != 0);
+  assert (nhdr.n_type == NT_PRSTATUS);
+  const Ebl_Core_Item *item;
+  for (item = items; item < items + nitems; item++)
+    if (strcmp (item->name, "pid") == 0)
+      break;
+  assert (item < items + nitems);
+  pid_t tid;
+  {
+    uint32_t val32 = *(const uint32_t *) (desc + item->offset);
+    val32 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
+	     ? be32toh (val32) : le32toh (val32));
+    tid = (int32_t) val32;
+    eu_static_assert (sizeof val32 <= sizeof tid);
+  }
+  /* core_next_thread already found this TID there.  */
+  assert (tid == INTUSE(dwfl_thread_tid) (thread));
+  desc += regs_offset;
+  for (size_t regloci = 0; regloci < nregloc; regloci++)
+    {
+      const Ebl_Register_Location *regloc = reglocs + regloci;
+      if (regloc->regno >= nregs)
+	continue;
+      assert (regloc->bits == 32 || regloc->bits == 64);
+      const char *reg_desc = desc + regloc->offset;
+      for (unsigned regno = regloc->regno;
+	   regno < MIN (regloc->regno + (regloc->count ?: 1U), nregs);
+	   regno++)
+	{
+	  /* PPC provides DWARF register 65 irrelevant for
+	     CFI which clashes with register 108 (LR) we need.
+	     LR (108) is provided earlier (in NT_PRSTATUS) than the # 65.
+	     FIXME: It depends now on their order in core notes.
+	     FIXME: It uses private function.  */
+	  if (__libdwfl_frame_reg_get (thread->unwound, regno, NULL))
+	    continue;
+	  Dwarf_Word val;
+	  switch (regloc->bits)
+	  {
+	    case 32:;
+	      uint32_t val32 = *(const uint32_t *) reg_desc;
+	      reg_desc += sizeof val32;
+	      val32 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
+		       ? be32toh (val32) : le32toh (val32));
+	      /* Do a host width conversion.  */
+	      val = val32;
+	      break;
+	    case 64:;
+	      uint64_t val64 = *(const uint64_t *) reg_desc;
+	      reg_desc += sizeof val64;
+	      val64 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
+		       ? be64toh (val64) : le64toh (val64));
+	      assert (sizeof (*thread->unwound->regs) == sizeof val64);
+	      val = val64;
+	      break;
+	    default:
+	      abort ();
+	  }
+	  /* Registers not valid for CFI are just ignored.  */
+	  INTUSE(dwfl_thread_state_registers) (thread, regno, 1, &val);
+	  reg_desc += regloc->pad;
+	}
+    }
+  return true;
+}
+
+static void
+core_detach (Dwfl *dwfl __attribute__ ((unused)), void *dwfl_arg)
+{
+  struct core_arg *core_arg = dwfl_arg;
+  ebl_closebackend (core_arg->ebl);
+  free (core_arg);
+}
+
+static const Dwfl_Thread_Callbacks core_thread_callbacks =
+{
+  core_next_thread,
+  core_memory_read,
+  core_set_initial_registers,
+  core_detach,
+  NULL, /* core_thread_detach */
+};
+
+bool
+internal_function
+__libdwfl_attach_state_for_core (Dwfl *dwfl, Elf *core)
+{
+  Ebl *ebl = ebl_openbackend (core);
+  if (ebl == NULL)
+    {
+      __libdwfl_seterrno (DWFL_E_LIBEBL);
+      return false;
+    }
+  size_t nregs = ebl_frame_nregs (ebl);
+  if (nregs == 0)
+    {
+      ebl_closebackend (ebl);
+      __libdwfl_seterrno (DWFL_E_LIBEBL);
+      return false;
+    }
+  GElf_Ehdr ehdr_mem, *ehdr = gelf_getehdr (core, &ehdr_mem);
+  if (ehdr == NULL)
+    {
+      ebl_closebackend (ebl);
+      __libdwfl_seterrno (DWFL_E_LIBELF);
+      return false;
+    }
+  assert (ehdr->e_type == ET_CORE);
+  size_t phnum;
+  if (elf_getphdrnum (core, &phnum) < 0)
+    {
+      ebl_closebackend (ebl);
+      __libdwfl_seterrno (DWFL_E_LIBELF);
+      return false;
+    }
+  pid_t pid = -1;
+  Elf_Data *note_data = NULL;
+  for (size_t cnt = 0; cnt < phnum; ++cnt)
+    {
+      GElf_Phdr phdr_mem, *phdr = gelf_getphdr (core, cnt, &phdr_mem);
+      if (phdr != NULL && phdr->p_type == PT_NOTE)
+	{
+	  note_data = elf_getdata_rawchunk (core, phdr->p_offset,
+					    phdr->p_filesz, ELF_T_NHDR);
+	  break;
+	}
+    }
+  if (note_data == NULL)
+    {
+      ebl_closebackend (ebl);
+      __libdwfl_seterrno (DWFL_E_LIBELF);
+      return NULL;
+    }
+  size_t offset = 0;
+  GElf_Nhdr nhdr;
+  size_t name_offset;
+  size_t desc_offset;
+  while (offset < note_data->d_size
+	 && (offset = gelf_getnote (note_data, offset,
+				    &nhdr, &name_offset, &desc_offset)) > 0)
+    {
+      /* Do not check NAME for now, help broken Linux kernels.  */
+      const char *name = note_data->d_buf + name_offset;
+      const char *desc = note_data->d_buf + desc_offset;
+      GElf_Word regs_offset;
+      size_t nregloc;
+      const Ebl_Register_Location *reglocs;
+      size_t nitems;
+      const Ebl_Core_Item *items;
+      if (! ebl_core_note (ebl, &nhdr, name,
+			   &regs_offset, &nregloc, &reglocs, &nitems, &items))
+	{
+	  /* This note may be just not recognized, skip it.  */
+	  continue;
+	}
+      if (nhdr.n_type != NT_PRPSINFO)
+	continue;
+      const Ebl_Core_Item *item;
+      for (item = items; item < items + nitems; item++)
+	if (strcmp (item->name, "pid") == 0)
+	  break;
+      if (item == items + nitems)
+	continue;
+      uint32_t val32 = *(const uint32_t *) (desc + item->offset);
+      val32 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
+		? be32toh (val32) : le32toh (val32));
+      pid = (int32_t) val32;
+      eu_static_assert (sizeof val32 <= sizeof pid);
+      break;
+    }
+  if (pid == -1)
+    {
+      /* No valid NT_PRPSINFO recognized in this CORE.  */
+      ebl_closebackend (ebl);
+      __libdwfl_seterrno (DWFL_E_BADELF);
+      return false;
+    }
+  struct core_arg *core_arg = malloc (sizeof *core_arg);
+  if (core_arg == NULL)
+    {
+      ebl_closebackend (ebl);
+      __libdwfl_seterrno (DWFL_E_NOMEM);
+      return false;
+    }
+  core_arg->core = core;
+  core_arg->note_data = note_data;
+  core_arg->thread_note_offset = 0;
+  core_arg->ebl = ebl;
+  if (! INTUSE(dwfl_attach_state) (dwfl, ebl_get_elfmachine (ebl), pid,
+				   &core_thread_callbacks, core_arg))
+    {
+      free (core_arg);
+      ebl_closebackend (ebl);
+      return false;
+    }
+  return true;
+}
diff --git a/libdwfl/linux-pid-attach.c b/libdwfl/linux-pid-attach.c
new file mode 100644
index 00000000..5ad58f6b
--- /dev/null
+++ b/libdwfl/linux-pid-attach.c
@@ -0,0 +1,282 @@
+/* Get Dwarf Frame state for target live PID process.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#include "libdwflP.h"
+#include <sys/ptrace.h>
+#include <sys/wait.h>
+#include <dirent.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#ifndef MAX
+# define MAX(a, b) ((a) > (b) ? (a) : (b))
+#endif
+
+struct pid_arg
+{
+  DIR *dir;
+  /* It is 0 if not used.  */
+  pid_t tid_attached;
+};
+
+static bool
+linux_proc_pid_is_stopped (pid_t pid)
+{
+  char buffer[64];
+  FILE *procfile;
+  bool retval, have_state;
+
+  snprintf (buffer, sizeof (buffer), "/proc/%ld/status", (long) pid);
+  procfile = fopen (buffer, "r");
+  if (procfile == NULL)
+    return false;
+
+  have_state = false;
+  while (fgets (buffer, sizeof (buffer), procfile) != NULL)
+    if (strncmp (buffer, "State:", 6) == 0)
+      {
+	have_state = true;
+	break;
+      }
+  retval = (have_state && strstr (buffer, "T (stopped)") != NULL);
+  fclose (procfile);
+  return retval;
+}
+
+static bool
+ptrace_attach (pid_t tid)
+{
+  if (ptrace (PTRACE_ATTACH, tid, NULL, NULL) != 0)
+    {
+      __libdwfl_seterrno (DWFL_E_ERRNO);
+      return false;
+    }
+  if (linux_proc_pid_is_stopped (tid))
+    {
+      /* Make sure there is a SIGSTOP signal pending even when the process is
+	 already State: T (stopped).  Older kernels might fail to generate
+	 a SIGSTOP notification in that case in response to our PTRACE_ATTACH
+	 above.  Which would make the waitpid below wait forever.  So emulate
+	 it.  Since there can only be one SIGSTOP notification pending this is
+	 safe.  See also gdb/linux-nat.c linux_nat_post_attach_wait.  */
+      syscall (__NR_tkill, tid, SIGSTOP);
+      ptrace (PTRACE_CONT, tid, NULL, NULL);
+    }
+  for (;;)
+    {
+      int status;
+      if (waitpid (tid, &status, __WALL) != tid || !WIFSTOPPED (status))
+	{
+	  int saved_errno = errno;
+	  ptrace (PTRACE_DETACH, tid, NULL, NULL);
+	  errno = saved_errno;
+	  __libdwfl_seterrno (DWFL_E_ERRNO);
+	  return false;
+	}
+      if (WSTOPSIG (status) == SIGSTOP)
+	break;
+      if (ptrace (PTRACE_CONT, tid, NULL,
+		  (void *) (uintptr_t) WSTOPSIG (status)) != 0)
+	{
+	  int saved_errno = errno;
+	  ptrace (PTRACE_DETACH, tid, NULL, NULL);
+	  errno = saved_errno;
+	  __libdwfl_seterrno (DWFL_E_ERRNO);
+	  return false;
+	}
+    }
+  return true;
+}
+
+static bool
+pid_memory_read (Dwfl *dwfl, Dwarf_Addr addr, Dwarf_Word *result, void *arg)
+{
+  struct pid_arg *pid_arg = arg;
+  pid_t tid = pid_arg->tid_attached;
+  assert (tid > 0);
+  Dwfl_Process *process = dwfl->process;
+  if (ebl_get_elfclass (process->ebl) == ELFCLASS64)
+    {
+#if SIZEOF_LONG == 8
+      errno = 0;
+      *result = ptrace (PTRACE_PEEKDATA, tid, (void *) (uintptr_t) addr, NULL);
+      return errno == 0;
+#else /* SIZEOF_LONG != 8 */
+      /* This should not happen.  */
+      return false;
+#endif /* SIZEOF_LONG != 8 */
+    }
+#if SIZEOF_LONG == 8
+  /* We do not care about reads unaliged to 4 bytes boundary.
+     But 0x...ffc read of 8 bytes could overrun a page.  */
+  bool lowered = (addr & 4) != 0;
+  if (lowered)
+    addr -= 4;
+#endif /* SIZEOF_LONG == 8 */
+  errno = 0;
+  *result = ptrace (PTRACE_PEEKDATA, tid, (void *) (uintptr_t) addr, NULL);
+  if (errno != 0)
+    return false;
+#if SIZEOF_LONG == 8
+# if BYTE_ORDER == BIG_ENDIAN
+  if (! lowered)
+    *result >>= 32;
+# else
+  if (lowered)
+    *result >>= 32;
+# endif
+#endif /* SIZEOF_LONG == 8 */
+  *result &= 0xffffffff;
+  return true;
+}
+
+static pid_t
+pid_next_thread (Dwfl *dwfl __attribute__ ((unused)), void *dwfl_arg,
+		 void **thread_argp)
+{
+  struct pid_arg *pid_arg = dwfl_arg;
+  struct dirent *dirent;
+  do
+    {
+      errno = 0;
+      dirent = readdir (pid_arg->dir);
+      if (dirent == NULL)
+	{
+	  if (errno != 0)
+	    {
+	      __libdwfl_seterrno (DWFL_E_ERRNO);
+	      return -1;
+	    }
+	  return 0;
+	}
+    }
+  while (strcmp (dirent->d_name, ".") == 0
+	 || strcmp (dirent->d_name, "..") == 0);
+  char *end;
+  errno = 0;
+  long tidl = strtol (dirent->d_name, &end, 10);
+  if (errno != 0)
+    {
+      __libdwfl_seterrno (DWFL_E_ERRNO);
+      return -1;
+    }
+  pid_t tid = tidl;
+  if (tidl <= 0 || (end && *end) || tid != tidl)
+    {
+      __libdwfl_seterrno (DWFL_E_PARSE_PROC);
+      return -1;
+    }
+  *thread_argp = dwfl_arg;
+  return tid;
+}
+
+/* Implement the ebl_set_initial_registers_tid setfunc callback.  */
+
+static bool
+pid_thread_state_registers_cb (const int firstreg,
+			       unsigned nregs,
+			       const Dwarf_Word *regs,
+			       void *arg)
+{
+  Dwfl_Thread *thread = (Dwfl_Thread *) arg;
+  return INTUSE(dwfl_thread_state_registers) (thread, firstreg, nregs, regs);
+}
+
+static bool
+pid_set_initial_registers (Dwfl_Thread *thread, void *thread_arg)
+{
+  struct pid_arg *pid_arg = thread_arg;
+  assert (pid_arg->tid_attached == 0);
+  pid_t tid = INTUSE(dwfl_thread_tid) (thread);
+  if (! ptrace_attach (tid))
+    return false;
+  pid_arg->tid_attached = tid;
+  Dwfl_Process *process = thread->process;
+  Ebl *ebl = process->ebl;
+  return ebl_set_initial_registers_tid (ebl, tid,
+					pid_thread_state_registers_cb, thread);
+}
+
+static void
+pid_detach (Dwfl *dwfl __attribute__ ((unused)), void *dwfl_arg)
+{
+  struct pid_arg *pid_arg = dwfl_arg;
+  closedir (pid_arg->dir);
+  free (pid_arg);
+}
+
+static void
+pid_thread_detach (Dwfl_Thread *thread, void *thread_arg)
+{
+  struct pid_arg *pid_arg = thread_arg;
+  pid_t tid = INTUSE(dwfl_thread_tid) (thread);
+  assert (pid_arg->tid_attached == tid);
+  pid_arg->tid_attached = 0;
+  ptrace (PTRACE_DETACH, tid, NULL, NULL);
+}
+
+static const Dwfl_Thread_Callbacks pid_thread_callbacks =
+{
+  pid_next_thread,
+  pid_memory_read,
+  pid_set_initial_registers,
+  pid_detach,
+  pid_thread_detach,
+};
+
+bool
+internal_function
+__libdwfl_attach_state_for_pid (Dwfl *dwfl, pid_t pid)
+{
+  char dirname[64];
+  int i = snprintf (dirname, sizeof (dirname), "/proc/%ld/task", (long) pid);
+  assert (i > 0 && i < (ssize_t) sizeof (dirname) - 1);
+  DIR *dir = opendir (dirname);
+  if (dir == NULL)
+    {
+      __libdwfl_seterrno (DWFL_E_ERRNO);
+      return false;
+    }
+  struct pid_arg *pid_arg = malloc (sizeof *pid_arg);
+  if (pid_arg == NULL)
+    {
+      closedir (dir);
+      __libdwfl_seterrno (DWFL_E_NOMEM);
+      return false;
+    }
+  pid_arg->dir = dir;
+  pid_arg->tid_attached = 0;
+  if (! INTUSE(dwfl_attach_state) (dwfl, EM_NONE, pid, &pid_thread_callbacks,
+				   pid_arg))
+    {
+      closedir (dir);
+      free (pid_arg);
+      return false;
+    }
+  return true;
+}
diff --git a/libdwfl/linux-proc-maps.c b/libdwfl/linux-proc-maps.c
index 4eaccdba..8863cc88 100644
--- a/libdwfl/linux-proc-maps.c
+++ b/libdwfl/linux-proc-maps.c
@@ -1,5 +1,5 @@
 /* Standard libdwfl callbacks for debugging a live Linux process.
-   Copyright (C) 2005-2010 Red Hat, Inc.
+   Copyright (C) 2005-2010, 2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -300,6 +300,13 @@ dwfl_linux_proc_report (Dwfl *dwfl, pid_t pid)
 
   fclose (f);
 
+  if (result == 0)
+    {
+      /* Possible error is ignored, DWFL still may be useful for non-unwinding
+	 operations.  */
+      __libdwfl_attach_state_for_pid (dwfl, pid);
+    }
+
   return result;
 }
 INTDEF (dwfl_linux_proc_report)
diff --git a/libdwfl/segment.c b/libdwfl/segment.c
index 496b4fdc..92769174 100644
--- a/libdwfl/segment.c
+++ b/libdwfl/segment.c
@@ -1,5 +1,5 @@
 /* Manage address space lookup table for libdwfl.
-   Copyright (C) 2008, 2009, 2010 Red Hat, Inc.
+   Copyright (C) 2008, 2009, 2010, 2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -28,16 +28,18 @@
 
 #include "libdwflP.h"
 
-static GElf_Addr
-segment_start (Dwfl *dwfl, GElf_Addr start)
+GElf_Addr
+internal_function
+__libdwfl_segment_start (Dwfl *dwfl, GElf_Addr start)
 {
   if (dwfl->segment_align > 1)
     start &= -dwfl->segment_align;
   return start;
 }
 
-static GElf_Addr
-segment_end (Dwfl *dwfl, GElf_Addr end)
+GElf_Addr
+internal_function
+__libdwfl_segment_end (Dwfl *dwfl, GElf_Addr end)
 {
   if (dwfl->segment_align > 1)
     end = (end + dwfl->segment_align - 1) & -dwfl->segment_align;
@@ -156,8 +158,8 @@ reify_segments (Dwfl *dwfl)
   for (Dwfl_Module *mod = dwfl->modulelist; mod != NULL; mod = mod->next)
     if (! mod->gc)
       {
-	const GElf_Addr start = segment_start (dwfl, mod->low_addr);
-	const GElf_Addr end = segment_end (dwfl, mod->high_addr);
+	const GElf_Addr start = __libdwfl_segment_start (dwfl, mod->low_addr);
+	const GElf_Addr end = __libdwfl_segment_end (dwfl, mod->high_addr);
 	bool resized = false;
 
 	int idx = lookup (dwfl, start, hint);
@@ -296,8 +298,9 @@ dwfl_report_segment (Dwfl *dwfl, int ndx, const GElf_Phdr *phdr, GElf_Addr bias,
       dwfl->lookup_module = NULL;
     }
 
-  GElf_Addr start = segment_start (dwfl, bias + phdr->p_vaddr);
-  GElf_Addr end = segment_end (dwfl, bias + phdr->p_vaddr + phdr->p_memsz);
+  GElf_Addr start = __libdwfl_segment_start (dwfl, bias + phdr->p_vaddr);
+  GElf_Addr end = __libdwfl_segment_end (dwfl,
+					 bias + phdr->p_vaddr + phdr->p_memsz);
 
   /* Coalesce into the last one if contiguous and matching.  */
   if (ndx != dwfl->lookup_tail_ndx
diff --git a/libebl/ChangeLog b/libebl/ChangeLog
index 1bc08689..57f9f46d 100644
--- a/libebl/ChangeLog
+++ b/libebl/ChangeLog
@@ -1,3 +1,13 @@
+2013-11-07  Jan Kratochvil  <jan.kratochvil@redhat.com>
+	    Mark Wielaard  <mjw@redhat.com>
+
+	* Makefile.am (gen_SOURCES): Add eblinitreg.c.
+	* ebl-hooks.h (set_initial_registers_tid): New entry.
+	* eblinitreg.c: New file.
+	* libebl.h (ebl_tid_registers_t): New definition.
+	(ebl_set_initial_registers_tid, ebl_frame_nregs): New declarations.
+	* libeblP.h (struct ebl): New entry frame_nregs.
+
 2013-10-06  Mark Wielaard  <mjw@redhat.com>
 
 	* libebl.h (ebl_abi_cfi): Document restrictions using register
diff --git a/libebl/Makefile.am b/libebl/Makefile.am
index 4d62fad1..4487c5f9 100644
--- a/libebl/Makefile.am
+++ b/libebl/Makefile.am
@@ -1,6 +1,6 @@
 ## Process this file with automake to create Makefile.in
 ##
-## Copyright (C) 2000-2010 Red Hat, Inc.
+## Copyright (C) 2000-2010, 2013 Red Hat, Inc.
 ## This file is part of elfutils.
 ##
 ## This file is free software; you can redistribute it and/or modify
@@ -54,7 +54,7 @@ gen_SOURCES = eblopenbackend.c eblclosebackend.c eblstrtab.c \
 	      eblreginfo.c eblnonerelocp.c eblrelativerelocp.c \
 	      eblsysvhashentrysize.c eblauxvinfo.c eblcheckobjattr.c \
 	      ebl_check_special_section.c ebl_syscall_abi.c eblabicfi.c \
-	      eblstother.c
+	      eblstother.c eblinitreg.c
 
 libebl_a_SOURCES = $(gen_SOURCES)
 
diff --git a/libebl/ebl-hooks.h b/libebl/ebl-hooks.h
index d3cf3e62..cb52fee4 100644
--- a/libebl/ebl-hooks.h
+++ b/libebl/ebl-hooks.h
@@ -1,5 +1,5 @@
 /* Backend hook signatures internal interface for libebl.
-   Copyright (C) 2000-2011 Red Hat, Inc.
+   Copyright (C) 2000-2011, 2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -155,5 +155,12 @@ int EBLHOOK(disasm) (const uint8_t **startp, const uint8_t *end,
    Function returns 0 on success and -1 on error.  */
 int EBLHOOK(abi_cfi) (Ebl *ebl, Dwarf_CIE *abi_info);
 
+/* Fetch process data from live TID and call SETFUNC one or more times.
+   Method should be present only when EBL_FRAME_NREGS > 0, otherwise the
+   backend doesn't support unwinding.  */
+bool EBLHOOK(set_initial_registers_tid) (pid_t tid,
+					 ebl_tid_registers_t *setfunc,
+					 void *arg);
+
 /* Destructor for ELF backend handle.  */
 void EBLHOOK(destr) (struct ebl *);
diff --git a/libebl/eblinitreg.c b/libebl/eblinitreg.c
new file mode 100644
index 00000000..8909c500
--- /dev/null
+++ b/libebl/eblinitreg.c
@@ -0,0 +1,51 @@
+/* Fetch live process Dwfl_Frame from PID.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <libeblP.h>
+#include <assert.h>
+
+bool
+ebl_set_initial_registers_tid (Ebl *ebl, pid_t tid,
+			       ebl_tid_registers_t *setfunc,
+			       void *arg)
+{
+  /* Otherwise caller could not allocate THREAD frame of proper size.
+     If set_initial_registers_tid is unsupported then FRAME_NREGS is zero.  */
+  assert (ebl->set_initial_registers_tid != NULL);
+  return ebl->set_initial_registers_tid (tid, setfunc, arg);
+}
+
+size_t
+ebl_frame_nregs (Ebl *ebl)
+{
+  return ebl == NULL ? 0 : ebl->frame_nregs;
+}
diff --git a/libebl/libebl.h b/libebl/libebl.h
index 990167a5..622f9e8d 100644
--- a/libebl/libebl.h
+++ b/libebl/libebl.h
@@ -1,5 +1,5 @@
 /* Interface for libebl.
-   Copyright (C) 2000-2010 Red Hat, Inc.
+   Copyright (C) 2000-2010, 2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -383,6 +383,26 @@ extern int ebl_auxv_info (Ebl *ebl, GElf_Xword a_type,
 			  const char **name, const char **format)
   __nonnull_attribute__ (1, 3, 4);
 
+/* Callback type for ebl_set_initial_registers_tid.  */
+typedef bool (ebl_tid_registers_t) (const int firstreg,
+				    unsigned nregs,
+				    const Dwarf_Word *regs,
+				    void *arg)
+  __nonnull_attribute__ (3);
+
+/* Callback to fetch process data from live TID.
+   EBL architecture has to have EBL_FRAME_NREGS > 0, otherwise the
+   backend doesn't support unwinding and this function call may crash.  */
+extern bool ebl_set_initial_registers_tid (Ebl *ebl,
+					   pid_t tid,
+					   ebl_tid_registers_t *setfunc,
+					   void *arg)
+  __nonnull_attribute__ (1, 3);
+
+/* Number of registers to allocate for ebl_set_initial_registers_tid.
+   EBL architecture can unwind iff EBL_FRAME_NREGS > 0.  */
+extern size_t ebl_frame_nregs (Ebl *ebl)
+  __nonnull_attribute__ (1);
 
 #ifdef __cplusplus
 }
diff --git a/libebl/libeblP.h b/libebl/libeblP.h
index 5ec26a4b..4f4137d5 100644
--- a/libebl/libeblP.h
+++ b/libebl/libeblP.h
@@ -1,5 +1,5 @@
 /* Internal definitions for interface for libebl.
-   Copyright (C) 2000-2009 Red Hat, Inc.
+   Copyright (C) 2000-2009, 2013 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -60,6 +60,10 @@ struct ebl
   /* Size of entry in Sysv-style hash table.  */
   int sysvhash_entrysize;
 
+  /* Number of registers to allocate for ebl_set_initial_registers_tid.
+     Ebl architecture can unwind iff FRAME_NREGS > 0.  */
+  size_t frame_nregs;
+
   /* Internal data.  */
   void *dlhandle;
 };
diff --git a/m4/ChangeLog b/m4/ChangeLog
index f82b0ca7..98de943b 100644
--- a/m4/ChangeLog
+++ b/m4/ChangeLog
@@ -1,3 +1,7 @@
+2013-11-07  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* biarch.m4: New file.
+
 2013-04-24  Mark Wielaard  <mjw@redhat.com>
 
 	* gettext.m4: Upgrade to gettext-0.18.2.
diff --git a/m4/biarch.m4 b/m4/biarch.m4
new file mode 100644
index 00000000..a15323e2
--- /dev/null
+++ b/m4/biarch.m4
@@ -0,0 +1,45 @@
+AC_DEFUN([utrace_CC_m32], [dnl
+AC_CACHE_CHECK([$CC option for 32-bit word size], utrace_cv_CC_m32, [dnl
+save_CC="$CC"
+utrace_cv_CC_m32=none
+for ut_try in -m32 -m31; do
+  [CC=`echo "$save_CC" | sed 's/ -m[36][241]//'`" $ut_try"]
+  AC_COMPILE_IFELSE([AC_LANG_SOURCE([[int foo (void) { return 1; }]])],
+		    [utrace_cv_CC_m32=$ut_try])
+  test x$utrace_cv_CC_m32 = xnone || break
+done
+CC="$save_CC"])])
+
+AC_DEFUN([utrace_HOST64], [AC_REQUIRE([utrace_CC_m32])
+AS_IF([test x$utrace_cv_CC_m32 != xnone], [dnl
+AC_CACHE_CHECK([for 64-bit host], utrace_cv_host64, [dnl
+AC_EGREP_CPP([@utrace_host64@], [#include <stdint.h>
+#if (UINTPTR_MAX > 0xffffffffUL)
+@utrace_host64@
+#endif],
+             utrace_cv_host64=yes, utrace_cv_host64=no)])
+AS_IF([test $utrace_cv_host64 = no],
+      [utrace_biarch=-m64 utrace_thisarch=$utrace_cv_CC_m32],
+      [utrace_biarch=$utrace_cv_CC_m32 utrace_thisarch=-m64])
+
+biarch_CC=`echo "$CC" | sed "s/ *${utrace_thisarch}//"`
+biarch_CC="$biarch_CC $utrace_biarch"])])
+
+AC_DEFUN([utrace_BIARCH], [AC_REQUIRE([utrace_HOST64])
+utrace_biarch_forced=no
+AC_ARG_WITH([biarch],
+	    AC_HELP_STRING([--with-biarch],
+			   [enable biarch tests despite build problems]),
+	    [AS_IF([test "x$with_biarch" != xno], [utrace_biarch_forced=yes])])
+AS_IF([test $utrace_biarch_forced = yes], [dnl
+utrace_cv_cc_biarch=yes
+AC_MSG_NOTICE([enabling biarch tests regardless using $biarch_CC])], [dnl
+AS_IF([test x$utrace_cv_CC_m32 != xnone], [dnl
+AC_CACHE_CHECK([whether $biarch_CC makes executables we can run],
+	       utrace_cv_cc_biarch, [dnl
+save_CC="$CC"
+CC="$biarch_CC"
+AC_RUN_IFELSE([AC_LANG_PROGRAM([], [])],
+	      utrace_cv_cc_biarch=yes, utrace_cv_cc_biarch=no)
+CC="$save_CC"])], [utrace_cv_cc_biarch=no])])
+AM_CONDITIONAL(BIARCH, [test $utrace_cv_cc_biarch = yes])])
diff --git a/src/ChangeLog b/src/ChangeLog
index 3012bf43..aebcb2ff 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2013-11-07  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* Makefile.am (bin_PROGRAMS): Add stack.
+	(stack_LDADD): New.
+	* stack.c: New file.
+
 2013-11-05  Mark Wielaard  <mjw@redhat.com>
 
 	* readelf.c (print_debug_ranges_section): Cast address to size_t
diff --git a/src/Makefile.am b/src/Makefile.am
index 674846d8..954a14ba 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1,6 +1,6 @@
 ## Process this file with automake to create Makefile.in
 ##
-## Copyright (C) 1996-2012 Red Hat, Inc.
+## Copyright (C) 1996-2013 Red Hat, Inc.
 ## This file is part of elfutils.
 ##
 ## This file is free software; you can redistribute it and/or modify
@@ -37,7 +37,7 @@ native_ld = @native_ld@
 base_cpu = @base_cpu@
 
 bin_PROGRAMS = readelf nm size strip ld elflint findtextrel addr2line \
-	       elfcmp objdump ranlib strings ar unstrip
+	       elfcmp objdump ranlib strings ar unstrip stack
 
 
 ld_dsos = libld_elf_i386_pic.a
@@ -115,6 +115,7 @@ ranlib_LDADD = libar.a $(libelf) $(libeu) $(libmudflap)
 strings_LDADD = $(libelf) $(libeu) $(libmudflap)
 ar_LDADD = libar.a $(libelf) $(libeu) $(libmudflap)
 unstrip_LDADD = $(libebl) $(libelf) $(libdw) $(libeu) $(libmudflap) -ldl
+stack_LDADD = $(libebl) $(libelf) $(libdw) $(libeu) $(libmudflap) -ldl
 
 ldlex.o: ldscript.c
 ldlex_no_Werror = yes
diff --git a/src/stack.c b/src/stack.c
new file mode 100644
index 00000000..948325d4
--- /dev/null
+++ b/src/stack.c
@@ -0,0 +1,174 @@
+/* Unwinding of frames like gstack/pstack.
+   Copyright (C) 2013 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+#include <assert.h>
+#include <argp.h>
+#include <error.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdio_ext.h>
+#include <locale.h>
+#include <fcntl.h>
+#include ELFUTILS_HEADER(dwfl)
+
+static bool verbose = false;
+
+static int
+frame_callback (Dwfl_Frame *state, void *arg)
+{
+  unsigned *framenop = arg;
+  Dwarf_Addr pc;
+  bool isactivation;
+  if (! dwfl_frame_pc (state, &pc, &isactivation))
+    {
+      error (0, 0, "%s", dwfl_errmsg (-1));
+      return DWARF_CB_ABORT;
+    }
+  Dwarf_Addr pc_adjusted = pc - (isactivation ? 0 : 1);
+
+  /* Get PC->SYMNAME.  */
+  Dwfl *dwfl = dwfl_thread_dwfl (dwfl_frame_thread (state));
+  Dwfl_Module *mod = dwfl_addrmodule (dwfl, pc_adjusted);
+  const char *symname = NULL;
+  if (mod)
+    symname = dwfl_module_addrname (mod, pc_adjusted);
+
+  // Try to find the address wide if possible.
+  static int width = 0;
+  if (width == 0 && mod)
+    {
+      Dwarf_Addr bias;
+      Elf *elf = dwfl_module_getelf (mod, &bias);
+      if (elf)
+	{
+	  GElf_Ehdr ehdr_mem;
+	  GElf_Ehdr *ehdr = gelf_getehdr (elf, &ehdr_mem);
+	  if (ehdr)
+	    width = ehdr->e_ident[EI_CLASS] == ELFCLASS32 ? 8 : 16;
+	}
+    }
+  if (width == 0)
+    width = 16;
+
+  printf ("#%-2u 0x%0*" PRIx64, (*framenop)++, width, (uint64_t) pc);
+  if (verbose)
+    printf ("%4s", ! isactivation ? "- 1" : "");
+  printf (" %s\n", symname);
+  return DWARF_CB_OK;
+}
+
+static int
+thread_callback (Dwfl_Thread *thread, void *thread_arg __attribute__ ((unused)))
+{
+  printf ("TID %ld:\n", (long) dwfl_thread_tid (thread));
+  unsigned frameno = 0;
+  switch (dwfl_thread_getframes (thread, frame_callback, &frameno))
+    {
+    case DWARF_CB_OK:
+    case DWARF_CB_ABORT:
+      break;
+    case -1:
+      error (0, 0, "dwfl_thread_getframes: %s", dwfl_errmsg (-1));
+      break;
+    default:
+      abort ();
+    }
+  return DWARF_CB_OK;
+}
+
+static error_t
+parse_opt (int key, char *arg __attribute__ ((unused)),
+	   struct argp_state *state)
+{
+  switch (key)
+    {
+    case ARGP_KEY_INIT:
+      state->child_inputs[0] = state->input;
+      break;
+
+    case 'v':
+      verbose = true;
+      break;
+
+    default:
+      return ARGP_ERR_UNKNOWN;
+    }
+  return 0;
+}
+
+int
+main (int argc, char **argv)
+{
+  /* We use no threads here which can interfere with handling a stream.  */
+  __fsetlocking (stdin, FSETLOCKING_BYCALLER);
+  __fsetlocking (stdout, FSETLOCKING_BYCALLER);
+  __fsetlocking (stderr, FSETLOCKING_BYCALLER);
+
+  /* Set locale.  */
+  (void) setlocale (LC_ALL, "");
+
+  const struct argp_option options[] =
+    {
+      { "verbose", 'v', NULL, 0, N_("Additionally show frames activation"), 0 },
+      { NULL, 0, NULL, 0, NULL, 0 }
+    };
+
+  const struct argp_child children[] =
+    {
+      { .argp = dwfl_standard_argp () },
+      { .argp = NULL },
+    };
+
+  const struct argp argp =
+    {
+      .options = options,
+      .parser = parse_opt,
+      .doc = N_("\
+Print a stack for each thread in a process or core file.\n\
+Only real user processes are supported, no kernel or process maps."),
+      .children = children
+    };
+
+  int remaining;
+  Dwfl *dwfl = NULL;
+  argp_parse (&argp, argc, argv, 0, &remaining, &dwfl);
+  assert (dwfl != NULL);
+  if (remaining != argc)
+    error (2, 0, "eu-stack [--debuginfo-path=<path>] {-p <process id>|"
+		 "--core=<file> [--executable=<file>]|--help}");
+
+  /* dwfl_linux_proc_report has been already called from dwfl_standard_argp's
+     parse_opt function.  */
+  if (dwfl_report_end (dwfl, NULL, NULL) != 0)
+    error (2, 0, "dwfl_report_end: %s", dwfl_errmsg (-1));
+
+  switch (dwfl_getthreads (dwfl, thread_callback, NULL))
+    {
+    case DWARF_CB_OK:
+      break;
+    case -1:
+      error (0, 0, "dwfl_getthreads: %s", dwfl_errmsg (-1));
+      break;
+    default:
+      abort ();
+    }
+  dwfl_end (dwfl);
+
+  return 0;
+}