[msan] Check for AVX regs using offset

[paulkirth]

Summary

glibc versions < 2.26 use different names for the fields.
However the layout is unchanged, so using the offset should be a
portable way to address this issue across platforms.

Fixes: https://github.com/llvm/llvm-project/issues/53014

[phosek]

LGTM

[paulkirth]

Add Missing Header

[phosek]

compiler-rt/test/msan/Linux/signal_mcontext2.cpp

5

I'd use stdint.h instead which is more consistent with other tests and avoids header dependency on C++ standard library.

[phosek]

In D116695#3223842, @paulkirth wrote:

Add Missing Header

Do we need the same header in the other tests as well?

[paulkirth]

Address comments regarding header

[paulkirth]

compiler-rt/test/msan/Linux/signal_mcontext2.cpp

5

good point

compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cpp

 #if !SANITIZER_ANDROID
   unsigned struct_statfs_sz = sizeof(struct statfs);
   unsigned struct_sockaddr_sz = sizeof(struct sockaddr);
 
   unsigned ucontext_t_sz(void *ctx) {
 #    if SANITIZER_LINUX && SANITIZER_X64
     // See kernel arch/x86/kernel/fpu/signal.c for details.
     const auto *fpregs = static_cast<ucontext_t *>(ctx)->uc_mcontext.fpregs;
-    if (fpregs->__glibc_reserved1[12] == FP_XSTATE_MAGIC1)
-      return reinterpret_cast<const char *>(fpregs) +
-             fpregs->__glibc_reserved1[13] - static_cast<const char *>(ctx);
+    // The member names differ across header versions, but the actual layout
+    // is always the same.  So avoid using members, just use arithmetic.
+    const uint32_t *after_xmm =
+        reinterpret_cast<const uint32_t *>(fpregs + 1) - 24;
+    if (after_xmm[12] == FP_XSTATE_MAGIC1)
+      return reinterpret_cast<const char *>(fpregs) + after_xmm[13] -
+             static_cast<const char *>(ctx);
 #    endif
     return sizeof(ucontext_t);
   }
 #  endif  // !SANITIZER_ANDROID
 
 #  if SANITIZER_LINUX
   unsigned struct_epoll_event_sz = sizeof(struct epoll_event);
   unsigned struct_sysinfo_sz = sizeof(struct sysinfo);

compiler-rt/test/msan/Linux/signal_mcontext.cpp

 // RUN: %clangxx_msan -fsanitize-memory-track-origins=2 -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
 
 #include <pthread.h>
 #include <sanitizer/msan_interface.h>
 #include <signal.h>
 #include <stdio.h>
 #include <ucontext.h>
 #include <unistd.h>
 
 void handler(int sig, siginfo_t *info, void *uctx) {
   __msan_check_mem_is_initialized(uctx, sizeof(ucontext_t));
 #if defined(__x86_64__)
   auto *mctx = &static_cast<ucontext_t *>(uctx)->uc_mcontext;
   if (auto *fpregs = mctx->fpregs) {
-    if (fpregs->__glibc_reserved1[12] == FP_XSTATE_MAGIC1) {
+    // The member names differ across header versions, but the actual layout
+    // is always the same.  So avoid using members, just use arithmetic.
+    const uint32_t *after_xmm =
+        reinterpret_cast<const uint32_t *>(fpregs + 1) - 24;
+    if (after_xmm[12] == FP_XSTATE_MAGIC1) {
       auto *xstate = reinterpret_cast<_xstate *>(mctx->fpregs);
       __msan_check_mem_is_initialized(xstate, sizeof(*xstate));
     }
   }
 #endif
 }
 
 __attribute__((noinline)) void poison_stack() {

compiler-rt/test/msan/Linux/signal_mcontext2.cpp

 // RUN: %clangxx_msan -fsanitize-memory-track-origins=2 -O1 %s -o %t && not %run %t 2>&1 | FileCheck %s
 
 // REQUIRES: x86_64-target-arch
 
 #include <pthread.h>
 #include <signal.h>
 #include <ucontext.h>
 
 void handler(int sig, siginfo_t *info, void *uctx) {
   volatile int uninit;
   auto *mctx = &static_cast<ucontext_t *>(uctx)->uc_mcontext;
   auto *fpregs = mctx->fpregs;
-  if (fpregs && fpregs->__glibc_reserved1[12] == FP_XSTATE_MAGIC1)
+  // The member names differ across header versions, but the actual layout
+  // is always the same.  So avoid using members, just use arithmetic.
+  const uint32_t *after_xmm =
+      reinterpret_cast<const uint32_t *>(fpregs + 1) - 24;
+  if (after_xmm[12] == FP_XSTATE_MAGIC1)
     reinterpret_cast<_xstate *>(mctx->fpregs)->ymmh.ymmh_space[0] = uninit;
   else
     mctx->gregs[REG_RAX] = uninit;
 }
 
 int main(int argc, char **argv) {
   struct sigaction act = {};
   act.sa_sigaction = handler;
   act.sa_flags = SA_SIGINFO;
   sigfillset(&act.sa_mask);
   sigaction(SIGPROF, &act, 0);
   pthread_kill(pthread_self(), SIGPROF);
   return 0;
 }
 
 // CHECK: WARNING: MemorySanitizer: