commit 7ff728a9779cdc8e0639c032dc45cc20f7b4af21
author Florian Mayer <fmayer@google.com> Fri Jun 03 14:33:08 2022 -0700
committer Copybara-Service <copybara-worker@google.com> Wed Sep 21 14:16:45 2022 -0700
tree 8750ef641cbbab5de44dd1928b7c03d3b427484e
parent 77b82eb53fb4f942f3d1c5407a30fccf7b7aeb93

[libunwind] Handle G in personality string

Tested with the following program:

```
static volatile int* x = nullptr;

void throws()  __attribute__((noinline)) {
  if (getpid() == 0)
    return;
  throw "error";
}

void maybe_throws()  __attribute__((noinline)) {
  volatile int y = 1;
  x = &y;
  throws();
  y = 2;
}

int main(int argc, char** argv) {
  int y;
  try {
    maybe_throws();
  } catch (const char* e) {
    //printf("Caught\n");
  }
  y = *x;
  printf("%d\n", y); // should be MTE failure.
  return 0;
}
```

Built using `clang++ -c -O2 -target aarch64-linux -fexceptions -march=armv8-a+memtag -fsanitize=memtag-heap,memtag-stack`

Currently only Android implements runtime support for MTE stack tagging.

Without this change, we crash on `__cxa_get_globals` when trying to catch
the exception (because the stack frame __cxa_get_globals frame will fail due
to tags left behind on the stack). With this change, we crash on the `y = *x;`
as expected, because the stack frame has been untagged, but the pointer hasn't.

Reviewed By: #libunwind, compnerd, MaskRay

Differential Revision: https://reviews.llvm.org/D128998

NOKEYCHECK=True
GitOrigin-RevId: a3153381af48b2e704750255a704748a13c4c4de

src/UnwindCursor.hpp

diff --git a/src/UnwindCursor.hpp b/src/UnwindCursor.hpp
index 27eca08..f118497 100644
--- a/src/UnwindCursor.hpp
+++ b/src/UnwindCursor.hpp
@@ -442,7 +442,7 @@
   virtual void setFloatReg(int, unw_fpreg_t) {
     _LIBUNWIND_ABORT("setFloatReg not implemented");
   }
-  virtual int step() { _LIBUNWIND_ABORT("step not implemented"); }
+  virtual int step(bool = false) { _LIBUNWIND_ABORT("step not implemented"); }
   virtual void getInfo(unw_proc_info_t *) {
     _LIBUNWIND_ABORT("getInfo not implemented");
   }
@@ -494,7 +494,7 @@
   virtual bool        validFloatReg(int);
   virtual unw_fpreg_t getFloatReg(int);
   virtual void        setFloatReg(int, unw_fpreg_t);
-  virtual int         step();
+  virtual int         step(bool = false);
   virtual void        getInfo(unw_proc_info_t *);
   virtual void        jumpto();
   virtual bool        isSignalFrame();
@@ -925,7 +925,7 @@
   virtual bool        validFloatReg(int);
   virtual unw_fpreg_t getFloatReg(int);
   virtual void        setFloatReg(int, unw_fpreg_t);
-  virtual int         step();
+  virtual int         step(bool stage2 = false);
   virtual void        getInfo(unw_proc_info_t *);
   virtual void        jumpto();
   virtual bool        isSignalFrame();
@@ -999,22 +999,21 @@
                          pint_t pc, uintptr_t dso_base);
   bool getInfoFromDwarfSection(pint_t pc, const UnwindInfoSections &sects,
                                             uint32_t fdeSectionOffsetHint=0);
-  int stepWithDwarfFDE() {
-    return DwarfInstructions<A, R>::stepWithDwarf(_addressSpace,
-                                              (pint_t)this->getReg(UNW_REG_IP),
-                                              (pint_t)_info.unwind_info,
-                                              _registers, _isSignalFrame);
+  int stepWithDwarfFDE(bool stage2) {
+    return DwarfInstructions<A, R>::stepWithDwarf(
+        _addressSpace, (pint_t)this->getReg(UNW_REG_IP),
+        (pint_t)_info.unwind_info, _registers, _isSignalFrame, stage2);
   }
 #endif
 
 #if defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
   bool getInfoFromCompactEncodingSection(pint_t pc,
                                             const UnwindInfoSections &sects);
-  int stepWithCompactEncoding() {
-  #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
+  int stepWithCompactEncoding(bool stage2 = false) {
+#if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
     if ( compactSaysUseDwarf() )
-      return stepWithDwarfFDE();
-  #endif
+      return stepWithDwarfFDE(stage2);
+#endif
     R dummy;
     return stepWithCompactEncoding(dummy);
   }
@@ -2796,8 +2795,8 @@
 #endif // defined(_LIBUNWIND_CHECK_LINUX_SIGRETURN) &&
        // defined(_LIBUNWIND_TARGET_S390X)
 
-template <typename A, typename R>
-int UnwindCursor<A, R>::step() {
+template <typename A, typename R> int UnwindCursor<A, R>::step(bool stage2) {
+  (void)stage2;
   // Bottom of stack is defined is when unwind info cannot be found.
   if (_unwindInfoMissing)
     return UNW_STEP_END;
@@ -2811,13 +2810,13 @@
 #endif
   {
 #if defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
-    result = this->stepWithCompactEncoding();
+    result = this->stepWithCompactEncoding(stage2);
 #elif defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
     result = this->stepWithSEHData();
 #elif defined(_LIBUNWIND_SUPPORT_TBTAB_UNWIND)
     result = this->stepWithTBTableData();
 #elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
-    result = this->stepWithDwarfFDE();
+    result = this->stepWithDwarfFDE(stage2);
 #elif defined(_LIBUNWIND_ARM_EHABI)
     result = this->stepWithEHABI();
 #else