Remove unnecessary padding in ucontext_t

- removed extra padding from ucontex_t on x86, x86_64 and mips
- force ucontext_t struct to use 64 bits for the sigmask on all arches
(previsouly wrong since sigset_t on arm and x86 is only 32 bits)
- arm and arm64 continue to use padding to match glibc sigset_t

This brings Bionic on par with the kernel w.r.t ucontext padding.

Bug: 12828904
Change-Id: Ia8915ace694ecb4695603a334e697985f4c3e7aa

1 files changed, 13 insertions, 6 deletions

diff --git a/libc/include/sys/ucontext.h b/libc/include/sys/ucontext.h
index d6c6b4317..f62380d8a 100644
--- a/libc/include/sys/ucontext.h
+++ b/libc/include/sys/ucontext.h
@@ -68,8 +68,13 @@ typedef struct ucontext {
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
-  sigset_t uc_sigmask;
-  char __padding[128 - sizeof(sigset_t)];
+  // Android has a wrong (smaller) sigset_t on ARM.
+  union {
+    sigset_t bionic;
+    uint32_t kernel[2];
+  } uc_sigmask;
+  // The kernel adds extra padding after uc_sigmask to match glibc sigset_t on ARM.
+  char __padding[120];
   unsigned long uc_regspace[128] __attribute__((__aligned__(8)));
 } ucontext_t;
 
@@ -83,6 +88,7 @@ typedef struct ucontext {
   struct ucontext *uc_link;
   stack_t uc_stack;
   sigset_t uc_sigmask;
+  // The kernel adds extra padding after uc_sigmask to match glibc sigset_t on ARM64.
   char __padding[128 - sizeof(sigset_t)];
   mcontext_t uc_mcontext;
 } ucontext_t;
@@ -146,8 +152,11 @@ typedef struct ucontext {
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
-  sigset_t uc_sigmask;
-  char __padding[128 - sizeof(sigset_t)];
+  // Android has a wrong (smaller) sigset_t on x86.
+  union {
+    sigset_t bionic;
+    uint32_t kernel[2];
+  } uc_sigmask;
   struct _libc_fpstate __fpregs_mem;
 } ucontext_t;
 
@@ -198,7 +207,6 @@ typedef struct ucontext {
   stack_t uc_stack;
   mcontext_t uc_mcontext;
   sigset_t uc_sigmask;
-  char __padding[128 - sizeof(sigset_t)];
 } ucontext_t;
 
 #elif defined(__mips64__)
@@ -275,7 +283,6 @@ typedef struct ucontext {
   stack_t uc_stack;
   mcontext_t uc_mcontext;
   sigset_t uc_sigmask;
-  char __padding[128 - sizeof(sigset_t)];
   struct _libc_fpstate __fpregs_mem;
 } ucontext_t;