[libunwind] Handle G in personality string

[fmayer]

Summary

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.

[fmayer]

fix unused argument error

[fmayer]

format

[fmayer]

fix mingw build

[fmayer]

build

[fmayer]

clang fmt

[fmayer]

fix build

[fmayer]

comment

[fmayer]

update comment

[fmayer]

In addition to the test described in the message, I ran the libunwind test suites on FVP with SANITIZE_TARGET=memtag-stack and they still pass.

[eugenis]

libunwind/src/DwarfInstructions.hpp

221

Is this right? I'd expect to untag from current frame SP to previous frame SP, not to CFA (which could be at arbitrary offset in the frame AFAIK).

[fmayer]

libunwind/src/DwarfInstructions.hpp

221

ARM64 ABI says this: "The CFA is the value of the stack pointer (sp) at the call site in the previous frame."

(see https://github.com/ARM-software/abi-aa/blob/main/aadwarf64/aadwarf64.rst#42canonical-frame-address)

[fmayer]

add comment

[eugenis]

This seems ok in general, but I'd like someone with better knowledge of the code to review.

libunwind/src/DwarfInstructions.hpp

221

SGTM but change the comment - this is not about SP in the previous frame at all, this is about CFA being at the bottom of the current stack frame.

libunwind/src/DwarfParser.hpp

54

whitespace here and below

libunwind/src/UnwindCursor.hpp

1019

Do we need MTE support here?

[fmayer]

address comments

libunwind/src/UnwindCursor.hpp

1019

I don't think so: This also doesn't handle the PAC BKey, and the plumbing through LLVM and the linker of that is the same as our 'G' flag.

[MaskRay]

Without this change, we crash on cxa_get_globals when trying to catch the exception (because the stack frame hadn't been cleared up).

cxa_get_globals => __cxa_get_globals

Can you describe the clang command line? It's unclear how MTE is used.

The description should mention the introduction of __unw_clean_step. The clean part in the name and the clean parameter feels unclear to me.

(because the stack frame hadn't been cleared up)

Can you elaborate what this means?

[MaskRay]

libunwind/src/DwarfInstructions.hpp

220

-16ULL

[MaskRay]

About __unw_clean_step:

libunwind/src/libunwind_ext.h provides a bunch of API which are not implemented by https://github.com/libunwind/libunwind .
Before we settle on an API there, it's worth raising an issue on https://github.com/libunwind/libunwind and giving them some time for the API design.

[fmayer]

In D128998#3721563, @MaskRay wrote:

About __unw_clean_step:

libunwind/src/libunwind_ext.h provides a bunch of API which are not implemented by https://github.com/libunwind/libunwind .
Before we settle on an API there, it's worth raising an issue on https://github.com/libunwind/libunwind and giving them some time for the API design.

AFAICT my change does not in fact expose a new API, because it does not use _LIBUNWIND_WEAK_ALIAS, so __unw_clean_step will remain hidden visiblity.

[fmayer]

libunwind/src/DwarfInstructions.hpp

220

Can you explain why this is preferred? At least for me, using only bitwise operators is more intuitive.

[fmayer]

In D128998#3723720, @fmayer wrote:

In D128998#3721563, @MaskRay wrote:

About __unw_clean_step:

libunwind/src/libunwind_ext.h provides a bunch of API which are not implemented by https://github.com/libunwind/libunwind .
Before we settle on an API there, it's worth raising an issue on https://github.com/libunwind/libunwind and giving them some time for the API design.

AFAICT my change does not in fact expose a new API, because it does not use _LIBUNWIND_WEAK_ALIAS, so __unw_clean_step will remain hidden visiblity.

Ping. Should I move the extern int __unw_clean_step(unw_cursor_t *); declaration out of libunwind_ext.h if I don't want it to be an API?

[MaskRay]

Can you describe the clang command line? It's unclear how MTE is used.

Unaddressed.

Should I move the extern int __unw_clean_step(unw_cursor_t *); declaration out of libunwind_ext.h if I don't want it to be an API?

Good idea. __unw_clean_step does not seem suitable to be an API when the nongnu libunwind discussion has not happened.

The clean part in the name and the clean parameter feels unclear to me.

And this.

[fmayer]

In D128998#3757020, @MaskRay wrote:

The clean part in the name and the clean parameter feels unclear to me.

And this.

This is meant to express that this cleans up the stack frame, and it cannot be used afterwards (because the tags will not match anymore). Is cleanup better? destroy_frame?

[compnerd]

libunwind/src/DwarfInstructions.hpp

224

Would be nice to split this over two lines.

libunwind/src/libunwind.cpp

186

I think that untag is better than clean - __unw_step_untag. We are untagging the memory and that makes it more clear.

[fmayer]

comments

libunwind/src/libunwind.cpp

186

OK. I wanted to keep this name generic in case we need to do other cleanup steps later, but we can also cross that bridge when/if we get there.

[danielkiss]

libunwind/src/libunwind.cpp

186

__unw_step is used in phase 1(search) and phase 2(apply).
maybe would be better to differentiate as unw_step_search and unw_step_apply (or similar) to make architecture agonistic.
For PAC we need to calculate the return value always but with MTE we could just untag memory when actually doing the unwinding.
same for step(bool untag = false); could be step(bool search_phase = false);

[fmayer]

libunwind/src/libunwind.cpp

186

I assume for step(bool search_phase = false) you meant step(bool apply_phase = false) (or step(bool search_phase = true)).

I'll hold off on further renames until we can get some consensus here.

[fmayer]

libunwind/src/libunwind.cpp

186

For PAC we need to calculate the return value always but with MTE we could just untag memory when actually doing the unwinding.

Also, we *must not* untag the frame in the search phase, because then we can cause tag mismatches in what you call the apply phase.

[fmayer]

libunwind/src/libunwind.cpp

186

Another naming option would be __unw_step_stage2

[compnerd]

libunwind/src/libunwind.cpp

186

I like __unw_step_stage2 better.

[danielkiss]

libunwind/src/libunwind.cpp

186

__unw_step_stage2 works for me too.
step(bool stage2 = false) would be it's pair IMHO.

[fmayer]

libunwind/src/libunwind.cpp

186

@MaskRay do you also agree with this name?

[MaskRay]

libunwind/src/libunwind.cpp

186

__unw_step_stage2 works for me, too.

[MaskRay]

stage2 is still a bit weird since we have phase1/phase2 distinction, but in the absence of a better name stage2 is fine to me.

[fmayer]

naming

[eugenis]

stage2 is fine with me, too
LGTM

[MaskRay]

libunwind/src/libunwind.cpp

185

Mixed comment markers.

Using // for everything should be fine.

[fmayer]

comment

[mgorny]

This change broke building with -DLIBUNWIND_ENABLE_CROSS_UNWINDING=ON:

$ ninja -C build -j1  -k99
ninja: Entering directory `build'
[1/5] Building CXX object libunwind/src/CMakeFiles/unwind_shared_objects.dir/libunwind.cpp.o
FAILED: libunwind/src/CMakeFiles/unwind_shared_objects.dir/libunwind.cpp.o 
/usr/bin/c++ -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/mgorny/git/llvm-bisect/libunwind/include -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wimplicit-fallthrough -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -fdata-sections -Os -DNDEBUG -fPIC -Werror=return-type -W -Wall -Wchar-subscripts -Wconversion -Wmismatched-tags -Wmissing-braces -Wno-unused-function -Wshadow -Wsign-compare -Wsign-conversion -Wstrict-aliasing=2 -Wstrict-overflow=4 -Wunused-parameter -Wunused-variable -Wwrite-strings -Wundef -Wno-suggest-override -Wno-error -pedantic -funwind-tables -nostdinc++ -D_DEBUG -UNDEBUG -fno-rtti -std=c++11  -fstrict-aliasing -fno-exceptions -fno-rtti -MD -MT libunwind/src/CMakeFiles/unwind_shared_objects.dir/libunwind.cpp.o -MF libunwind/src/CMakeFiles/unwind_shared_objects.dir/libunwind.cpp.o.d -o libunwind/src/CMakeFiles/unwind_shared_objects.dir/libunwind.cpp.o -c /home/mgorny/git/llvm-bisect/libunwind/src/libunwind.cpp
In file included from /home/mgorny/git/llvm-bisect/libunwind/src/DwarfParser.hpp:22,
                 from /home/mgorny/git/llvm-bisect/libunwind/src/EHHeaderParser.hpp:17,
                 from /home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp:23,
                 from /home/mgorny/git/llvm-bisect/libunwind/src/libunwind.cpp:30:
/home/mgorny/git/llvm-bisect/libunwind/src/Registers.hpp:2871:5: warning: "__mips_isa_rev" is not defined, evaluates to 0 [-Wundef]
 2871 | #if __mips_isa_rev != 6
      |     ^~~~~~~~~~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/Registers.hpp:3195:5: warning: "__mips_isa_rev" is not defined, evaluates to 0 [-Wundef]
 3195 | #if __mips_isa_rev != 6
      |     ^~~~~~~~~~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/Registers.hpp: In member function ‘bool libunwind::Registers_ppc64::validVectorRegister(int) const’:
/home/mgorny/git/llvm-bisect/libunwind/src/Registers.hpp:1549:54: warning: unused parameter ‘regNum’ [-Wunused-parameter]
 1549 | inline bool Registers_ppc64::validVectorRegister(int regNum) const {
      |                                                  ~~~~^~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp: In static member function ‘static int64_t libunwind::LocalAddressSpace::getSLEB128(pint_t&, pint_t)’:
/home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp:256:42: warning: conversion to ‘long unsigned int’ from ‘int64_t’ {aka ‘long int’} may change the sign of the result [-Wsign-conversion]
  256 |     result |= (uint64_t)(byte & 0x7f) << bit;
      |                                          ^~~
/home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp:261:26: warning: conversion to ‘long long unsigned int’ from ‘int64_t’ {aka ‘long int’} may change the sign of the result [-Wsign-conversion]
  261 |     result |= (-1ULL) << bit;
      |                          ^~~
/home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp:261:12: warning: conversion to ‘int64_t’ {aka ‘long int’} from ‘long long unsigned int’ may change the sign of the result [-Wsign-conversion]
  261 |     result |= (-1ULL) << bit;
      |     ~~~~~~~^~~~~~~~~~~~~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/libunwind.cpp: At global scope:
/home/mgorny/git/llvm-bisect/libunwind/src/libunwind.cpp:39:23: warning: type-punning to incomplete type might break strict-aliasing rules [-Wstrict-aliasing]
   39 |     (unw_addr_space_t)&LocalAddressSpace::sThisAddressSpace;
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/DwarfInstructions.hpp: Assembler messages:
/home/mgorny/git/llvm-bisect/libunwind/src/DwarfInstructions.hpp:224: Error: unknown pseudo-op: `.arch_extension'
/home/mgorny/git/llvm-bisect/libunwind/src/DwarfInstructions.hpp:225: Error: no such instruction: `stg %rax,[%rax]'
[2/5] Building CXX object libunwind/src/CMakeFiles/unwind_static_objects.dir/libunwind.cpp.o
FAILED: libunwind/src/CMakeFiles/unwind_static_objects.dir/libunwind.cpp.o 
/usr/bin/c++ -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/mgorny/git/llvm-bisect/libunwind/include -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wimplicit-fallthrough -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -fdata-sections -Os -DNDEBUG -Werror=return-type -W -Wall -Wchar-subscripts -Wconversion -Wmismatched-tags -Wmissing-braces -Wno-unused-function -Wshadow -Wsign-compare -Wsign-conversion -Wstrict-aliasing=2 -Wstrict-overflow=4 -Wunused-parameter -Wunused-variable -Wwrite-strings -Wundef -Wno-suggest-override -Wno-error -pedantic -funwind-tables -nostdinc++ -D_DEBUG -UNDEBUG -fno-rtti -std=c++11  -fstrict-aliasing -fno-exceptions -fno-rtti -MD -MT libunwind/src/CMakeFiles/unwind_static_objects.dir/libunwind.cpp.o -MF libunwind/src/CMakeFiles/unwind_static_objects.dir/libunwind.cpp.o.d -o libunwind/src/CMakeFiles/unwind_static_objects.dir/libunwind.cpp.o -c /home/mgorny/git/llvm-bisect/libunwind/src/libunwind.cpp
In file included from /home/mgorny/git/llvm-bisect/libunwind/src/DwarfParser.hpp:22,
                 from /home/mgorny/git/llvm-bisect/libunwind/src/EHHeaderParser.hpp:17,
                 from /home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp:23,
                 from /home/mgorny/git/llvm-bisect/libunwind/src/libunwind.cpp:30:
/home/mgorny/git/llvm-bisect/libunwind/src/Registers.hpp:2871:5: warning: "__mips_isa_rev" is not defined, evaluates to 0 [-Wundef]
 2871 | #if __mips_isa_rev != 6
      |     ^~~~~~~~~~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/Registers.hpp:3195:5: warning: "__mips_isa_rev" is not defined, evaluates to 0 [-Wundef]
 3195 | #if __mips_isa_rev != 6
      |     ^~~~~~~~~~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/Registers.hpp: In member function ‘bool libunwind::Registers_ppc64::validVectorRegister(int) const’:
/home/mgorny/git/llvm-bisect/libunwind/src/Registers.hpp:1549:54: warning: unused parameter ‘regNum’ [-Wunused-parameter]
 1549 | inline bool Registers_ppc64::validVectorRegister(int regNum) const {
      |                                                  ~~~~^~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp: In static member function ‘static int64_t libunwind::LocalAddressSpace::getSLEB128(pint_t&, pint_t)’:
/home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp:256:42: warning: conversion to ‘long unsigned int’ from ‘int64_t’ {aka ‘long int’} may change the sign of the result [-Wsign-conversion]
  256 |     result |= (uint64_t)(byte & 0x7f) << bit;
      |                                          ^~~
/home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp:261:26: warning: conversion to ‘long long unsigned int’ from ‘int64_t’ {aka ‘long int’} may change the sign of the result [-Wsign-conversion]
  261 |     result |= (-1ULL) << bit;
      |                          ^~~
/home/mgorny/git/llvm-bisect/libunwind/src/AddressSpace.hpp:261:12: warning: conversion to ‘int64_t’ {aka ‘long int’} from ‘long long unsigned int’ may change the sign of the result [-Wsign-conversion]
  261 |     result |= (-1ULL) << bit;
      |     ~~~~~~~^~~~~~~~~~~~~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/libunwind.cpp: At global scope:
/home/mgorny/git/llvm-bisect/libunwind/src/libunwind.cpp:39:23: warning: type-punning to incomplete type might break strict-aliasing rules [-Wstrict-aliasing]
   39 |     (unw_addr_space_t)&LocalAddressSpace::sThisAddressSpace;
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/mgorny/git/llvm-bisect/libunwind/src/DwarfInstructions.hpp: Assembler messages:
/home/mgorny/git/llvm-bisect/libunwind/src/DwarfInstructions.hpp:224: Error: unknown pseudo-op: `.arch_extension'
/home/mgorny/git/llvm-bisect/libunwind/src/DwarfInstructions.hpp:225: Error: no such instruction: `stg %rax,[%rax]'
ninja: build stopped: cannot make progress due to previous errors.

Please fix or revert.

[fmayer]

In D128998#3826710, @mgorny wrote:

This change broke building with -DLIBUNWIND_ENABLE_CROSS_UNWINDING=ON:

Thanks for the report and sorry about that, sent https://reviews.llvm.org/D134969.

[JOE1994]

libunwind/src/DwarfInstructions.hpp

224

This added inline assembly (stg instruction).
According to the ARM instruction reference guide, stg instruction is only supported in ARMv8.5 and later.

Since this change (D128998), I can no longer build libunwind on my ARMv8.1 machine.
The assembler gives the following error:

/tmp/ccim5Evd.s: Assembler messages:
/tmp/ccim5Evd.s:9031: Error: unknown architectural extension `memtag'
/tmp/ccim5Evd.s:9031: Error: unknown mnemonic `stg' -- `stg x2,[x2]'
/tmp/ccim5Evd.s:9040: Error: unknown architectural extension `memtag'
/tmp/ccim5Evd.s:9040: Error: unknown mnemonic `stg' -- `stg x2,[x2]'

Is there a way to add a guard to only insert the stg instruction in supported ISAs?

[MaskRay]

libunwind/src/DwarfInstructions.hpp

224

You'll need to use the latest Clang to build the file. Older Clang is not supported. See https://libcxx.llvm.org/BuildingLibcxx.html

[JOE1994]

libunwind/src/DwarfInstructions.hpp

224

Thank you so much for the pointer. It helped me tremendously :)

libunwind/src/DwarfInstructions.hpp

 /// architecture
 template <typename A, typename R>
 class DwarfInstructions {
 public:
   typedef typename A::pint_t pint_t;
   typedef typename A::sint_t sint_t;
 
   static int stepWithDwarf(A &addressSpace, pint_t pc, pint_t fdeStart,
-                           R &registers, bool &isSignalFrame);
+                           R &registers, bool &isSignalFrame, bool clean);
 
 private:
 
   enum {
     DW_X86_64_RET_ADDR = 16
   };
 
   enum {
bool DwarfInstructions<A, R>::getRA_SIGN_STATE(A &addressSpace, R registers,
   // Only bit[0] is meaningful.
   return raSignState & 0x01;
 }
 #endif
 
 template <typename A, typename R>
 int DwarfInstructions<A, R>::stepWithDwarf(A &addressSpace, pint_t pc,
                                            pint_t fdeStart, R &registers,
-                                           bool &isSignalFrame) {
+                                           bool &isSignalFrame, bool clean) {
   FDE_Info fdeInfo;
   CIE_Info cieInfo;
   if (CFI_Parser<A>::decodeFDE(addressSpace, fdeStart, &fdeInfo,
                                &cieInfo) == NULL) {
     PrologInfo prolog;
     if (CFI_Parser<A>::parseFDEInstructions(addressSpace, fdeInfo, cieInfo, pc,
                                             R::getArch(), &prolog)) {
       // get pointer to cfa (architecture specific)
       pint_t cfa = getCFA(addressSpace, prolog, registers);
 
-       // restore registers that DWARF says were saved
+      (void)clean;
+#if defined(_LIBUNWIND_TARGET_AARCH64)
+      if (clean && cieInfo.mteTaggedFrame) {
+        pint_t sp = registers.getSP();
+        pint_t p = sp;
+        // AArch64 doesn't require the value of SP to be 16-byte aligned at
+        // all times, only at memory accesses and public interfaces. Thus, a
+        // signal could arrive at a point where SP is not aligned properly.
+        // In that case, the kernel fixes up [1] the signal frame, but we
+        // still have a misaligned SP in the previous frame. If that signal
+        // handler caused stack unwinding, we would have an unaligned SP.
+        // We do not need to fix up the CFA, as that is the SP at a "public
+        // interface".
+        // [1]:
+        // https://github.com/torvalds/linux/blob/1930a6e739c4b4a654a69164dbe39e554d228915/arch/arm64/kernel/signal.c#L718
+        p &= ~15ULL;
+        for (; p < cfa; p += 16) {
+          __asm__ __volatile__(
+              ".arch_extension memtag\nstg %[Ptr], [%[Ptr]]\n" ::[Ptr] "r"(p)
+              : "memory");
+        }
+      }
+#endif
       R newRegisters = registers;
 
       // Typically, the CFA is the stack pointer at the call site in
       // the previous frame. However, there are scenarios in which this is not
       // true. For example, if we switched to a new stack. In that case, the
       // value of the previous SP might be indicated by a CFI directive.
       //
       // We set the SP here to the CFA, allowing for it to be overridden

libunwind/src/DwarfParser.hpp

struct CIE_Info {
     pint_t    personality;
     uint32_t  codeAlignFactor;
     int       dataAlignFactor;
     bool      isSignalFrame;
     bool      fdesHaveAugmentationData;
     uint8_t   returnAddressRegister;
 #if defined(_LIBUNWIND_TARGET_AARCH64)
     bool      addressesSignedWithBKey;
+    bool mteTaggedFrame;
 #endif
   };
 
   /// Information about an FDE (Frame Description Entry)
   struct FDE_Info {
     pint_t  fdeStart;
     pint_t  fdeLength;
     pint_t  fdeInstructions;
const char *CFI_Parser<A>::parseCIE(A &addressSpace, pint_t cie,
   cieInfo->personalityOffsetInCIE = 0;
   cieInfo->personality = 0;
   cieInfo->codeAlignFactor = 0;
   cieInfo->dataAlignFactor = 0;
   cieInfo->isSignalFrame = false;
   cieInfo->fdesHaveAugmentationData = false;
 #if defined(_LIBUNWIND_TARGET_AARCH64)
   cieInfo->addressesSignedWithBKey = false;
+  cieInfo->mteTaggedFrame = false;
 #endif
   cieInfo->cieStart = cie;
   pint_t p = cie;
   pint_t cieLength = (pint_t)addressSpace.get32(p);
   p += 4;
   pint_t cieContentEnd = p + cieLength;
   if (cieLength == 0xffffffff) {
     // 0xffffffff means length is really next 8 bytes
for (pint_t s = strStart; addressSpace.get8(s) != '\0'; ++s) {
         break;
       case 'S':
         cieInfo->isSignalFrame = true;
         break;
 #if defined(_LIBUNWIND_TARGET_AARCH64)
       case 'B':
         cieInfo->addressesSignedWithBKey = true;
         break;
+      case 'G':
+        cieInfo->mteTaggedFrame = true;
+        break;
 #endif
       default:
         // ignore unknown letters
         break;
       }
     }
   }
   cieInfo->cieLength = cieContentEnd - cieInfo->cieStart;

libunwind/src/UnwindCursor.hpp

virtual bool validFloatReg(int) {
     _LIBUNWIND_ABORT("validFloatReg not implemented");
   }
   virtual unw_fpreg_t getFloatReg(int) {
     _LIBUNWIND_ABORT("getFloatReg not implemented");
   }
   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");
   }
   virtual void jumpto() { _LIBUNWIND_ABORT("jumpto not implemented"); }
   virtual bool isSignalFrame() {
     _LIBUNWIND_ABORT("isSignalFrame not implemented");
   }
   virtual bool getFunctionName(char *, size_t, unw_word_t *) {
public:
                       UnwindCursor(A &as, void *threadArg);
   virtual             ~UnwindCursor() {}
   virtual bool        validReg(int);
   virtual unw_word_t  getReg(int);
   virtual void        setReg(int, unw_word_t);
   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();
   virtual bool        getFunctionName(char *buf, size_t len, unw_word_t *off);
   virtual void        setInfoBasedOnIPRegister(bool isReturnAddress = false);
   virtual const char *getRegisterName(int num);
 #ifdef __arm__
   virtual void        saveVFPAsX();
public:
                       UnwindCursor(A &as, void *threadArg);
   virtual             ~UnwindCursor() {}
   virtual bool        validReg(int);
   virtual unw_word_t  getReg(int);
   virtual void        setReg(int, unw_word_t);
   virtual bool        validFloatReg(int);
   virtual unw_fpreg_t getFloatReg(int);
   virtual void        setFloatReg(int, unw_fpreg_t);
-  virtual int         step();
+  virtual int step(bool clean = false);
   virtual void        getInfo(unw_proc_info_t *);
   virtual void        jumpto();
   virtual bool        isSignalFrame();
   virtual bool        getFunctionName(char *buf, size_t len, unw_word_t *off);
   virtual void        setInfoBasedOnIPRegister(bool isReturnAddress = false);
   virtual const char *getRegisterName(int num);
 #ifdef __arm__
   virtual void        saveVFPAsX();

 #endif
 
 #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
   bool getInfoFromFdeCie(const typename CFI_Parser<A>::FDE_Info &fdeInfo,
                          const typename CFI_Parser<A>::CIE_Info &cieInfo,
                          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 clean) {
+    return DwarfInstructions<A, R>::stepWithDwarf(
+        _addressSpace, (pint_t)this->getReg(UNW_REG_IP),
+        (pint_t)_info.unwind_info, _registers, _isSignalFrame, clean);
   }
 #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 clean = false) {
     if ( compactSaysUseDwarf() )
-      return stepWithDwarfFDE();
-  #endif
+      return stepWithDwarfFDE(clean);
     R dummy;
     return stepWithCompactEncoding(dummy);
   }
 
 #if defined(_LIBUNWIND_TARGET_X86_64)
   int stepWithCompactEncoding(Registers_x86_64 &) {
     return CompactUnwinder_x86_64<A>::stepWithCompactEncoding(
         _info.format, _info.start_ip, _addressSpace, _registers);
   }
 #endif
int UnwindCursor<A, R>::stepThroughSigReturn(Registers_s390x &) {
   uint32_t signo = _addressSpace.get32(pSigno);
   _isSignalFrame = (signo != 4 && signo != 5 && signo != 8);
 
   return UNW_STEP_SUCCESS;
 }
 #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 clean) {
+  (void)clean;
   // Bottom of stack is defined is when unwind info cannot be found.
   if (_unwindInfoMissing)
     return UNW_STEP_END;
 
   // Use unwinding info to modify register set as if function returned.
   int result;
 #if defined(_LIBUNWIND_CHECK_LINUX_SIGRETURN)
   if (_isSigReturn) {
     result = this->stepThroughSigReturn();
   } else
 #endif
   {
 #if defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
-    result = this->stepWithCompactEncoding();
+    result = this->stepWithCompactEncoding(clean);
 #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(clean);
 #elif defined(_LIBUNWIND_ARM_EHABI)
     result = this->stepWithEHABI();
 #else
   #error Need _LIBUNWIND_SUPPORT_COMPACT_UNWIND or \
               _LIBUNWIND_SUPPORT_SEH_UNWIND or \
               _LIBUNWIND_SUPPORT_DWARF_UNWIND or \
               _LIBUNWIND_ARM_EHABI
 #endif

libunwind/src/UnwindLevel1.c

unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *exception_object) {
   // uc is initialized by __unw_getcontext in the parent frame. The first stack
   // frame walked is unwind_phase2.
   unsigned framesWalked = 1;
   // Walk each frame until we reach where search phase said to stop.
   while (true) {
 
     // Ask libunwind to get next frame (skip over first which is
     // _Unwind_RaiseException).
-    int stepResult = __unw_step(cursor);
+    int stepResult = __unw_clean_step(cursor);
     if (stepResult == 0) {
       _LIBUNWIND_TRACE_UNWINDING(
-          "unwind_phase2(ex_ojb=%p): __unw_step() reached "
+          "unwind_phase2(ex_ojb=%p): __unw_clean_step() reached "
           "bottom => _URC_END_OF_STACK",
           (void *)exception_object);
       return _URC_END_OF_STACK;
     } else if (stepResult < 0) {
       _LIBUNWIND_TRACE_UNWINDING(
-          "unwind_phase2(ex_ojb=%p): __unw_step failed => "
+          "unwind_phase2(ex_ojb=%p): __unw_clean_step failed => "
           "_URC_FATAL_PHASE1_ERROR",
           (void *)exception_object);
       return _URC_FATAL_PHASE2_ERROR;
     }
 
     // Get info about this frame.
     unw_word_t sp;
     unw_proc_info_t frameInfo;
unwind_phase2_forced(unw_context_t *uc, unw_cursor_t *cursor,
                      _Unwind_Exception *exception_object,
                      _Unwind_Stop_Fn stop, void *stop_parameter) {
   __unw_init_local(cursor, uc);
 
   // uc is initialized by __unw_getcontext in the parent frame. The first stack
   // frame walked is unwind_phase2_forced.
   unsigned framesWalked = 1;
   // Walk each frame until we reach where search phase said to stop
-  while (__unw_step(cursor) > 0) {
+  while (__unw_clean_step(cursor) > 0) {
 
     // Update info about this frame.
     unw_proc_info_t frameInfo;
     if (__unw_get_proc_info(cursor, &frameInfo) != UNW_ESUCCESS) {
-      _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): __unw_step "
-                                 "failed => _URC_END_OF_STACK",
-                                 (void *)exception_object);
+      _LIBUNWIND_TRACE_UNWINDING(
+          "unwind_phase2_forced(ex_ojb=%p): __unw_clean_step "
       return _URC_FATAL_PHASE2_ERROR;
     }
 
 #ifndef NDEBUG
     // When tracing, print state information.
     if (_LIBUNWIND_TRACING_UNWINDING) {
       char functionBuf[512];
       const char *functionName = functionBuf;

libunwind/src/libunwind.cpp

 /// Move cursor to next frame.
 _LIBUNWIND_HIDDEN int __unw_step(unw_cursor_t *cursor) {
   _LIBUNWIND_TRACE_API("__unw_step(cursor=%p)", static_cast<void *>(cursor));
   AbstractUnwindCursor *co = (AbstractUnwindCursor *)cursor;
   return co->step();
 }
 _LIBUNWIND_WEAK_ALIAS(__unw_step, unw_step)
 
+/// Move cursor to next frame.
+_LIBUNWIND_HIDDEN int __unw_clean_step(unw_cursor_t *cursor) {
+  _LIBUNWIND_TRACE_API("__unw_clean_step(cursor=%p)",
+                       static_cast<void *>(cursor));
+  AbstractUnwindCursor *co = (AbstractUnwindCursor *)cursor;
+  return co->step(true);
+}
+
 /// Get unwind info at cursor position in stack frame.
 _LIBUNWIND_HIDDEN int __unw_get_proc_info(unw_cursor_t *cursor,
                                           unw_proc_info_t *info) {
   _LIBUNWIND_TRACE_API("__unw_get_proc_info(cursor=%p, &info=%p)",
                        static_cast<void *>(cursor), static_cast<void *>(info));
   AbstractUnwindCursor *co = (AbstractUnwindCursor *)cursor;
   co->getInfo(info);
   if (info->end_ip == 0)

libunwind/src/libunwind_ext.h

 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 extern int __unw_getcontext(unw_context_t *);
 extern int __unw_init_local(unw_cursor_t *, unw_context_t *);
 extern int __unw_step(unw_cursor_t *);
+extern int __unw_clean_step(unw_cursor_t *);
 extern int __unw_get_reg(unw_cursor_t *, unw_regnum_t, unw_word_t *);
 extern int __unw_get_fpreg(unw_cursor_t *, unw_regnum_t, unw_fpreg_t *);
 extern int __unw_set_reg(unw_cursor_t *, unw_regnum_t, unw_word_t);
 extern int __unw_set_fpreg(unw_cursor_t *, unw_regnum_t, unw_fpreg_t);
 extern int __unw_resume(unw_cursor_t *);
 
 #ifdef __arm__
 /* Save VFP registers in FSTMX format (instead of FSTMD). */