commit 6a570ad85b81eb53f0245268c7315409de2520e0
merge: b38db0d0c3651fa83d5bc81f795fde7680f72033 45a49d9b4df748ab9f2b1267f8183b6574fea206
author: eeight
date: 2021-02-24T23:44:48+03:00
revision: 7897977

    IGNIETFERRO-603 Record exception backtraces during stack unwinding
    
    REVIEW: 1637486

--- a/include/unwind.h
+++ b/include/unwind.h
@@ -396,6 +396,21 @@ extern EXCEPTION_DISPOSITION _GCC_specific_handler(EXCEPTION_RECORD *exc,
                                                    _Unwind_Personality_Fn pers);
 #endif
 
+#ifdef _YNDX_LIBUNWIND_ENABLE_EXCEPTION_BACKTRACE
+
+#define _YNDX_LIBUNWIND_EXCEPTION_BACKTRACE_SIZE 128
+// NB. How to compute:
+// offsetof(__cxa_exception, unwindHeader) + (sizeof(_Unwind_Backtrace_Buffer) + 15) / 16 * 16 - sizeof(_Unwind_Backtrace_Buffer)
+// Correctness of this value is static_assert'd in contrib/libs/cxxsupp/libcxxrta/exception.cc
+#define _YNDX_LIBUNWIND_EXCEPTION_BACKTRACE_MAGIC_OFFSET 104
+#define _YNDX_LIBUNWIND_EXCEPTION_BACKTRACE_PRIMARY_CLASS 0xacadacadull
+#define _YNDX_LIBUNWIND_EXCEPTION_BACKTRACE_DEPENDENT_CLASS 0xddddacadull
+
+typedef struct _Unwind_Backtrace_Buffer {
+    size_t size;
+    void* backtrace[_YNDX_LIBUNWIND_EXCEPTION_BACKTRACE_SIZE];
+} _Unwind_Backtrace_Buffer;
+#endif
 #ifdef __cplusplus
 }
 #endif
--- a/src/UnwindLevel1.c
+++ b/src/UnwindLevel1.c
@@ -38,6 +38,15 @@ static _Unwind_Reason_Code
 unwind_phase1(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *exception_object) {
   __unw_init_local(cursor, uc);
 
+#ifdef _YNDX_LIBUNWIND_ENABLE_EXCEPTION_BACKTRACE
+  _Unwind_Backtrace_Buffer* backtrace_buffer =
+      exception_object->exception_class == _YNDX_LIBUNWIND_EXCEPTION_BACKTRACE_PRIMARY_CLASS ||
+          exception_object->exception_class == _YNDX_LIBUNWIND_EXCEPTION_BACKTRACE_DEPENDENT_CLASS ?
+      (_Unwind_Backtrace_Buffer *)(
+          (char*)exception_object - _YNDX_LIBUNWIND_EXCEPTION_BACKTRACE_MAGIC_OFFSET) - 1
+      : NULL;
+#endif
+
   // Walk each frame looking for a place to stop.
   while (true) {
     // Ask libunwind to get next frame (skip over first which is
@@ -57,6 +66,14 @@ unwind_phase1(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *except
       return _URC_FATAL_PHASE1_ERROR;
     }
 
+#ifdef _YNDX_LIBUNWIND_ENABLE_EXCEPTION_BACKTRACE
+    if (backtrace_buffer && backtrace_buffer->size < _YNDX_LIBUNWIND_EXCEPTION_BACKTRACE_SIZE) {
+        unw_word_t pc;
+        __unw_get_reg(cursor, UNW_REG_IP, &pc);
+        backtrace_buffer->backtrace[backtrace_buffer->size++] = (void *)pc;
+    }
+#endif
+
     // See if frame has code to run (has personality routine).
     unw_proc_info_t frameInfo;
     unw_word_t sp;