[Unwind] Harmonise exception class for EHABI spec.

[danielkiss]

Summary

EHABI defines the exception class as char[8] instead of uint64_t [1].
For ABI compatibility the ABI the definition needs to be updated.

[1] https://github.com/ARM-software/abi-aa/blob/main/ehabi32/ehabi32.rst#82language-independent-unwinding-types-and-functions

[manojgupta]

Thanks Daniel. We still have a problem with pthread_cancel but this resolves the immediate crash.

[MaskRay]

LGTM.

[hans]

libunwind/src/UnwindLevel1-gcc-ext.c

112

We're seeing a -Wincompatible-pointer-types warning here (which we treat as an error) in Chromium:

../../buildtools/third_party/libunwind/trunk/src/UnwindLevel1-gcc-ext.c:112:10: error: incompatible pointer types passing '_Unwind_Exception_Class *' (aka 'uint8_t (*)[8]') to parameter of type 'char *' [-Werror,-Wincompatible-pointer-types]
  strcpy(&ex.exception_class, "CLNGUNW");
         ^~~~~~~~~~~~~~~~~~~

I see in libunwind/test/forceunwind.pass.cpp you're casting the pointer to char*, maybe that's needed here too?

[hans]

libunwind/src/UnwindLevel1-gcc-ext.c

112

https://reviews.llvm.org/D109168 fixes it for me locally.

[danielkiss]

libunwind/src/UnwindLevel1-gcc-ext.c

112

@hans Thanks for the patch, LGTM.

libcxxabi/test/forced_unwind1.pass.cpp

 
 static void cleanup(_Unwind_Reason_Code, struct _Unwind_Exception* exc) {
   bits |= 8;
   delete exc;
 }
 
 static void forced_unwind() {
   _Unwind_Exception* exc = new _Unwind_Exception;
-  exc->exception_class = 0;
+  memset(&exc->exception_class, 0, sizeof(exc->exception_class));
   exc->exception_cleanup = cleanup;
   _Unwind_ForcedUnwind(exc, Stop<_Unwind_Stop_Fn>::stop, 0);
   abort();
 }
 
 static void test() {
   try {
     C four(4);

libcxxabi/test/forced_unwind2.pass.cpp

static _Unwind_Reason_Code stop(int, _Unwind_Action actions, type,
     if (actions & _UA_END_OF_STACK)
       abort();
     return _URC_NO_REASON;
   }
 };
 
 static void forced_unwind() {
   _Unwind_Exception* exc = new _Unwind_Exception;
-  exc->exception_class = 0;
+  memset(&exc->exception_class, 0, sizeof(exc->exception_class));
   exc->exception_cleanup = 0;
   _Unwind_ForcedUnwind(exc, Stop<_Unwind_Stop_Fn>::stop, 0);
   abort();
 }
 
 static void test() noexcept { forced_unwind(); }
 
 static void terminate() { exit(0); }

libunwind/include/unwind.h

 #include "unwind_arm_ehabi.h"
 #else
 #include "unwind_itanium.h"
 #endif
 
 typedef _Unwind_Reason_Code (*_Unwind_Stop_Fn)
     (int version,
      _Unwind_Action actions,
-     uint64_t exceptionClass,
+     _Unwind_Exception_Class exceptionClass,
      _Unwind_Exception* exceptionObject,
      struct _Unwind_Context* context,
      void* stop_parameter);
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 

libunwind/include/unwind_arm_ehabi.h

 /* Undocumented flag for force unwinding. */
 static const _Unwind_State _US_FORCE_UNWIND           = 8;
 
 typedef uint32_t _Unwind_EHT_Header;
 
 struct _Unwind_Control_Block;
 typedef struct _Unwind_Control_Block _Unwind_Control_Block;
 #define _Unwind_Exception _Unwind_Control_Block /* Alias */
+typedef uint8_t _Unwind_Exception_Class[8];
 
 struct _Unwind_Control_Block {
-  uint64_t exception_class;
+  _Unwind_Exception_Class exception_class;
   void (*exception_cleanup)(_Unwind_Reason_Code, _Unwind_Control_Block*);
 
   /* Unwinder cache, private fields for the unwinder's use */
   struct {
     uint32_t reserved1; /* init reserved1 to 0, then don't touch */
     uint32_t reserved2;
     uint32_t reserved3;
     uint32_t reserved4;

libunwind/include/unwind_itanium.h

 //===----------------------------------------------------------------------===//
 
 #ifndef __ITANIUM_UNWIND_H__
 #define __ITANIUM_UNWIND_H__
 
 struct _Unwind_Context;   // opaque
 struct _Unwind_Exception; // forward declaration
 typedef struct _Unwind_Exception _Unwind_Exception;
+typedef uint64_t _Unwind_Exception_Class;
 
 struct _Unwind_Exception {
-  uint64_t exception_class;
+  _Unwind_Exception_Class exception_class;
   void (*exception_cleanup)(_Unwind_Reason_Code reason,
                             _Unwind_Exception *exc);
 #if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
   uintptr_t private_[6];
 #else
   uintptr_t private_1; // non-zero means forced unwind
   uintptr_t private_2; // holds sp that phase1 found for phase2 to use
 #endif

libunwind/src/UnwindLevel1-gcc-ext.c

_Unwind_Backtrace(_Unwind_Trace_Fn callback, void *ref) {
 
   _LIBUNWIND_TRACE_API("_Unwind_Backtrace(callback=%p)",
                        (void *)(uintptr_t)callback);
 
 #if defined(_LIBUNWIND_ARM_EHABI)
   // Create a mock exception object for force unwinding.
   _Unwind_Exception ex;
   memset(&ex, '\0', sizeof(ex));
-  ex.exception_class = 0x434C4E47554E5700; // CLNGUNW\0
+  strcpy(&ex.exception_class, "CLNGUNW");
 #endif
 
   // walk each frame
   while (true) {
     _Unwind_Reason_Code result;
 
 #if !defined(_LIBUNWIND_ARM_EHABI)
     // ask libunwind to get next frame (skip over first frame which is

libunwind/test/forceunwind.pass.cpp

 #include <sys/types.h>
 #include <unistd.h>
 #include <unwind.h>
 
 void foo();
 _Unwind_Exception ex;
 
 _Unwind_Reason_Code stop(int version, _Unwind_Action actions,
-                         uint64_t exceptionClass,
+                         _Unwind_Exception_Class exceptionClass,
                          _Unwind_Exception *exceptionObject,
                          struct _Unwind_Context *context,
                          void *stop_parameter) {
   assert(version == 1);
   assert((actions & _UA_FORCE_UNWIND) != 0);
   (void)exceptionClass;
   assert(exceptionObject == &ex);
   assert(stop_parameter == &foo);
__attribute__((noinline)) void foo() {
 
   // Arm EHABI defines struct _Unwind_Control_Block as exception
   // object. Ensure struct _Unwind_Exception* work there too,
   // because _Unwind_Exception in this case is just an alias.
   struct _Unwind_Exception *e = &ex;
 #if defined(_LIBUNWIND_ARM_EHABI)
   // Create a mock exception object.
   memset(e, '\0', sizeof(*e));
-  e->exception_class = 0x434C4E47554E5700; // CLNGUNW\0
+  strcpy(reinterpret_cast<char *>(&e->exception_class), "CLNGUNW");
 #endif
   _Unwind_ForcedUnwind(e, stop, (void *)&foo);
 }
 
 int main() {
   foo();
   return -2;
 }