[hwasan] Fix top PC in error stack trace being off by 1 instruction.

[eugenis]

Summary

GetStackTrace treats top PC as a return address from an error reporting
function, and adjusts it down by 1 instruction. This is not necessary in
a signal handler, so adjust PC up to compensate.

[eugenis]

No test because I don't see a reliable way to trigger bad debug info for the previous instruction with a C/C++ source...
With this change, tests pass both before and after https://reviews.llvm.org/D52125

[kcc]

LGTM

lib/hwasan/hwasan_linux.cc

static bool HwasanOnSIGTRAP(int signo, siginfo_t *info, ucontext_t *uc) {
   AccessInfo ai = GetAccessInfo(info, uc);
   if (!ai.is_store && !ai.is_load)
     return false;
 
   InternalMmapVector<BufferedStackTrace> stack_buffer(1);
   BufferedStackTrace *stack = stack_buffer.data();
   stack->Reset();
   SignalContext sig{info, uc};
-  GetStackTrace(stack, kStackTraceMax, sig.pc, sig.bp, uc,
-                common_flags()->fast_unwind_on_fatal);
+  GetStackTrace(stack, kStackTraceMax, StackTrace::GetNextInstructionPc(sig.pc),
+                sig.bp, uc, common_flags()->fast_unwind_on_fatal);
 
   ReportTagMismatch(stack, ai.addr, ai.size, ai.is_store);
 
   ++hwasan_report_count;
   if (flags()->halt_on_error || !ai.recover)
     Die();
 
 #if defined(__aarch64__)
   uc->uc_mcontext.pc += 4;
 #elif defined(__x86_64__)
 #else
 # error Unsupported architecture
 #endif
   return true;
 }
 
 static void OnStackUnwind(const SignalContext &sig, const void *,
                           BufferedStackTrace *stack) {
-  GetStackTrace(stack, kStackTraceMax, sig.pc, sig.bp, sig.context,
-                common_flags()->fast_unwind_on_fatal);
+  GetStackTrace(stack, kStackTraceMax, StackTrace::GetNextInstructionPc(sig.pc),
+                sig.bp, sig.context, common_flags()->fast_unwind_on_fatal);
 }
 
 void HwasanOnDeadlySignal(int signo, void *info, void *context) {
   // Probably a tag mismatch.
   if (signo == SIGTRAP)
     if (HwasanOnSIGTRAP(signo, (siginfo_t *)info, (ucontext_t*)context))
       return;
 
   HandleDeadlySignal(info, context, GetTid(), &OnStackUnwind, nullptr);
 }
 
 
 } // namespace __hwasan
 
 #endif // SANITIZER_FREEBSD || SANITIZER_LINUX || SANITIZER_NETBSD