Improve backtrace formatting.

Show the symbol offset, when available.

Centralized formatting of native stack traces in libcorkscrew.
It's handy for automated tools if all stacks look the same.
Since we already made them all look them same, we might as well
do the formatting in just one place.

Do not strip the Thumb bit on ARM.  This fixes an off-by-one
issue that could happen when resolving a PC that was at the
very beginning of a Thumb function, since the symbol table would
have the Thumb bit set but since we stripped the bit from our
PC, we would be looking for an address one byte before the
one listed in the symbol table.  It's also quite useful to see
whether a given function is executing in Thumb mode just by glancing
at the PC.

Change-Id: Icaa29add85ce0bcafe24d5ce2098e138d809e2ab

5 files changed, 84 insertions, 29 deletions

diff --git a/debuggerd/utility.c b/debuggerd/utility.c
index 64e59809..2ccf947e 100644
--- a/debuggerd/utility.c
+++ b/debuggerd/utility.c
@@ -65,16 +65,10 @@ static void dump_backtrace(const ptrace_context_t* context __attribute((unused))
     backtrace_symbol_t backtrace_symbols[STACK_DEPTH];
     get_backtrace_symbols_ptrace(context, backtrace, frames, backtrace_symbols);
     for (size_t i = 0; i < frames; i++) {
-        const backtrace_symbol_t* symbol = &backtrace_symbols[i];
-        const char* map_name = symbol->map_name ? symbol->map_name : "<unknown>";
-        const char* symbol_name = symbol->demangled_name ? symbol->demangled_name : symbol->name;
-        if (symbol_name) {
-            _LOG(tfd, !at_fault, "    #%02d  pc %08x  %s (%s)\n",
-                    (int)i, symbol->relative_pc, map_name, symbol_name);
-        } else {
-            _LOG(tfd, !at_fault, "    #%02d  pc %08x  %s\n",
-                    (int)i, symbol->relative_pc, map_name);
-        }
+        char line[MAX_BACKTRACE_LINE_LENGTH];
+        format_backtrace_line(i, &backtrace[i], &backtrace_symbols[i],
+                line, MAX_BACKTRACE_LINE_LENGTH);
+        _LOG(tfd, !at_fault, "    %s\n", line);
     }
     free_backtrace_symbols(backtrace_symbols, frames);
 }
@@ -94,12 +88,23 @@ static void dump_stack_segment(const ptrace_context_t* context, int tfd, pid_t t
         if (symbol) {
             char* demangled_name = demangle_symbol_name(symbol->name);
             const char* symbol_name = demangled_name ? demangled_name : symbol->name;
+            uint32_t offset = stack_content - (mi->start + symbol->start);
             if (!i && label >= 0) {
-                _LOG(tfd, only_in_tombstone, "    #%02d  %08x  %08x  %s (%s)\n",
-                        label, *sp, stack_content, mi ? mi->name : "", symbol_name);
+                if (offset) {
+                    _LOG(tfd, only_in_tombstone, "    #%02d  %08x  %08x  %s (%s+%u)\n",
+                            label, *sp, stack_content, mi ? mi->name : "", symbol_name, offset);
+                } else {
+                    _LOG(tfd, only_in_tombstone, "    #%02d  %08x  %08x  %s (%s)\n",
+                            label, *sp, stack_content, mi ? mi->name : "", symbol_name);
+                }
             } else {
-                _LOG(tfd, only_in_tombstone, "         %08x  %08x  %s (%s)\n",
-                        *sp, stack_content, mi ? mi->name : "", symbol_name);
+                if (offset) {
+                    _LOG(tfd, only_in_tombstone, "         %08x  %08x  %s (%s+%u)\n",
+                            *sp, stack_content, mi ? mi->name : "", symbol_name, offset);
+                } else {
+                    _LOG(tfd, only_in_tombstone, "         %08x  %08x  %s (%s)\n",
+                            *sp, stack_content, mi ? mi->name : "", symbol_name);
+                }
             }
             free(demangled_name);
         } else {
diff --git a/include/corkscrew/backtrace.h b/include/corkscrew/backtrace.h
index 157d0293..556ad04c 100644
--- a/include/corkscrew/backtrace.h
+++ b/include/corkscrew/backtrace.h
@@ -41,10 +41,12 @@ typedef struct {
  * Describes the symbols associated with a backtrace frame.
  */
 typedef struct {
-    uintptr_t relative_pc;       /* relative PC offset from the start of the library,
+    uintptr_t relative_pc;       /* relative frame PC offset from the start of the library,
                                     or the absolute PC if the library is unknown */
+    uintptr_t relative_symbol_addr; /* relative offset of the symbol from the start of the
+                                    library or 0 if the library is unknown */
     char* map_name;              /* executable or library name, or NULL if unknown */
-    char* name;                  /* symbol name, or NULL if unknown */
+    char* symbol_name;           /* symbol name, or NULL if unknown */
     char* demangled_name;        /* demangled symbol name, or NULL if unknown */
 } backtrace_symbol_t;
 
@@ -95,6 +97,17 @@ void get_backtrace_symbols_ptrace(const ptrace_context_t* context,
  */
 void free_backtrace_symbols(backtrace_symbol_t* backtrace_symbols, size_t frames);
 
+enum {
+    // A hint for how big to make the line buffer for format_backtrace_line
+    MAX_BACKTRACE_LINE_LENGTH = 800,
+};
+
+/**
+ * Formats a line from a backtrace as a zero-terminated string into the specified buffer.
+ */
+void format_backtrace_line(unsigned frameNumber, const backtrace_frame_t* frame,
+        const backtrace_symbol_t* symbol, char* buffer, size_t bufferSize);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/libcorkscrew/arch-arm/backtrace-arm.c b/libcorkscrew/arch-arm/backtrace-arm.c
index cf9a5ab3..5b911648 100644
--- a/libcorkscrew/arch-arm/backtrace-arm.c
+++ b/libcorkscrew/arch-arm/backtrace-arm.c
@@ -146,6 +146,7 @@ static uintptr_t get_exception_handler(const memory_t* memory,
     }
 
     uintptr_t handler = 0;
+    int32_t handler_index = -1;
     if (exidx_start) {
         uint32_t low = 0;
         uint32_t high = exidx_size;
@@ -153,10 +154,12 @@ static uintptr_t get_exception_handler(const memory_t* memory,
             uint32_t index = (low + high) / 2;
             uintptr_t entry = exidx_start + index * 8;
             uint32_t entry_prel_pc;
+            ALOGV("XXX low=%u, high=%u, index=%u", low, high, index);
             if (!try_get_word(memory, entry, &entry_prel_pc)) {
                 break;
             }
             uintptr_t entry_pc = prel_to_absolute(entry, entry_prel_pc);
+            ALOGV("XXX entry_pc=0x%08x", entry_pc);
             if (pc < entry_pc) {
                 high = index;
                 continue;
@@ -168,6 +171,7 @@ static uintptr_t get_exception_handler(const memory_t* memory,
                     break;
                 }
                 uintptr_t next_entry_pc = prel_to_absolute(next_entry, next_entry_prel_pc);
+                ALOGV("XXX next_entry_pc=0x%08x", next_entry_pc);
                 if (pc >= next_entry_pc) {
                     low = index + 1;
                     continue;
@@ -184,17 +188,18 @@ static uintptr_t get_exception_handler(const memory_t* memory,
             } else if (entry_handler != EXIDX_CANTUNWIND) {
                 handler = prel_to_absolute(entry_handler_ptr, entry_handler);
             }
+            handler_index = index;
             break;
         }
     }
     if (mi) {
         ALOGV("get_exception_handler: pc=0x%08x, module='%s', module_start=0x%08x, "
-                "exidx_start=0x%08x, exidx_size=%d, handler=0x%08x",
-                pc, mi->name, mi->start, exidx_start, exidx_size, handler);
+                "exidx_start=0x%08x, exidx_size=%d, handler=0x%08x, handler_index=%d",
+                pc, mi->name, mi->start, exidx_start, exidx_size, handler, handler_index);
     } else {
         ALOGV("get_exception_handler: pc=0x%08x, "
-                "exidx_start=0x%08x, exidx_size=%d, handler=0x%08x",
-                pc, exidx_start, exidx_size, handler);
+                "exidx_start=0x%08x, exidx_size=%d, handler=0x%08x, handler_index=%d",
+                pc, exidx_start, exidx_size, handler, handler_index);
     }
     return handler;
 }
@@ -464,11 +469,10 @@ uintptr_t rewind_pc_arch(const memory_t* memory, uintptr_t pc) {
          * 18896:       4798            blx     r3
          * 18898:       b001            add     sp, #4
          */
-        pc &= ~1;
         uint16_t prev1, prev2;
-        if (try_get_half_word(memory, pc - 4, &prev1)
+        if (try_get_half_word(memory, pc - 5, &prev1)
             && ((prev1 & 0xf000) == 0xf000)
-            && try_get_half_word(memory, pc - 2, &prev2)
+            && try_get_half_word(memory, pc - 3, &prev2)
             && ((prev2 & 0xe000) == 0xe000)) {
             pc -= 4; // long offset
         } else {
diff --git a/libcorkscrew/backtrace.c b/libcorkscrew/backtrace.c
index 857b7417..fa215742 100644
--- a/libcorkscrew/backtrace.c
+++ b/libcorkscrew/backtrace.c
@@ -213,8 +213,9 @@ ssize_t unwind_backtrace_ptrace(pid_t tid, const ptrace_context_t* context,
 
 static void init_backtrace_symbol(backtrace_symbol_t* symbol, uintptr_t pc) {
     symbol->relative_pc = pc;
+    symbol->relative_symbol_addr = 0;
     symbol->map_name = NULL;
-    symbol->name = NULL;
+    symbol->symbol_name = NULL;
     symbol->demangled_name = NULL;
 }
 
@@ -235,8 +236,10 @@ void get_backtrace_symbols(const backtrace_frame_t* backtrace, size_t frames,
 #if HAVE_DLADDR
             Dl_info info;
             if (dladdr((const void*)frame->absolute_pc, &info) && info.dli_sname) {
-                symbol->name = strdup(info.dli_sname);
-                symbol->demangled_name = demangle_symbol_name(symbol->name);
+                symbol->relative_symbol_addr = (uintptr_t)info.dli_saddr
+                        - (uintptr_t)info.dli_fbase;
+                symbol->symbol_name = strdup(info.dli_sname);
+                symbol->demangled_name = demangle_symbol_name(symbol->symbol_name);
             }
 #endif
         }
@@ -262,8 +265,9 @@ void get_backtrace_symbols_ptrace(const ptrace_context_t* context,
             }
         }
         if (s) {
-            symbol->name = strdup(s->name);
-            symbol->demangled_name = demangle_symbol_name(symbol->name);
+            symbol->relative_symbol_addr = s->start;
+            symbol->symbol_name = strdup(s->name);
+            symbol->demangled_name = demangle_symbol_name(symbol->symbol_name);
         }
     }
 }
@@ -272,8 +276,30 @@ void free_backtrace_symbols(backtrace_symbol_t* backtrace_symbols, size_t frames
     for (size_t i = 0; i < frames; i++) {
         backtrace_symbol_t* symbol = &backtrace_symbols[i];
         free(symbol->map_name);
-        free(symbol->name);
+        free(symbol->symbol_name);
         free(symbol->demangled_name);
         init_backtrace_symbol(symbol, 0);
     }
 }
+
+void format_backtrace_line(unsigned frameNumber, const backtrace_frame_t* frame,
+        const backtrace_symbol_t* symbol, char* buffer, size_t bufferSize) {
+    const char* mapName = symbol->map_name ? symbol->map_name : "<unknown>";
+    const char* symbolName = symbol->demangled_name ? symbol->demangled_name : symbol->symbol_name;
+    size_t fieldWidth = (bufferSize - 80) / 2;
+    if (symbolName) {
+        uint32_t pc_offset = symbol->relative_pc - symbol->relative_symbol_addr;
+        if (pc_offset) {
+            snprintf(buffer, bufferSize, "#%02d  pc %08x  %.*s (%.*s+%u)",
+                    frameNumber, symbol->relative_pc, fieldWidth, mapName,
+                    fieldWidth, symbolName, pc_offset);
+        } else {
+            snprintf(buffer, bufferSize, "#%02d  pc %08x  %.*s (%.*s)",
+                    frameNumber, symbol->relative_pc, fieldWidth, mapName,
+                    fieldWidth, symbolName);
+        }
+    } else {
+        snprintf(buffer, bufferSize, "#%02d  pc %08x  %.*s",
+                frameNumber, symbol->relative_pc, fieldWidth, mapName);
+    }
+}
diff --git a/libcorkscrew/symbol_table.c b/libcorkscrew/symbol_table.c
index 8257c773..1b97180c 100644
--- a/libcorkscrew/symbol_table.c
+++ b/libcorkscrew/symbol_table.c
@@ -47,6 +47,7 @@ static int bcompar(const void *key, const void *element) {
 
 symbol_table_t* load_symbol_table(const char *filename) {
     symbol_table_t* table = NULL;
+    ALOGV("Loading symbol table from '%s'.", filename);
 
     int fd = open(filename, O_RDONLY);
     if (fd < 0) {
@@ -154,6 +155,9 @@ symbol_table_t* load_symbol_table(const char *filename) {
                 table->symbols[symbol_index].name = strdup(dynstr + dynsyms[i].st_name);
                 table->symbols[symbol_index].start = dynsyms[i].st_value;
                 table->symbols[symbol_index].end = dynsyms[i].st_value + dynsyms[i].st_size;
+                ALOGV("  [%d] '%s' 0x%08x-0x%08x (DYNAMIC)",
+                        symbol_index, table->symbols[symbol_index].name,
+                        table->symbols[symbol_index].start, table->symbols[symbol_index].end);
                 symbol_index += 1;
             }
         }
@@ -169,6 +173,9 @@ symbol_table_t* load_symbol_table(const char *filename) {
                 table->symbols[symbol_index].name = strdup(str + syms[i].st_name);
                 table->symbols[symbol_index].start = syms[i].st_value;
                 table->symbols[symbol_index].end = syms[i].st_value + syms[i].st_size;
+                ALOGV("  [%d] '%s' 0x%08x-0x%08x",
+                        symbol_index, table->symbols[symbol_index].name,
+                        table->symbols[symbol_index].start, table->symbols[symbol_index].end);
                 symbol_index += 1;
             }
         }