Libgcc unwind backend (#11)

CMakeLists.txt

@@ -59,6 +59,7 @@ option(CPPTRACE_GET_SYMBOLS_WITH_ADDR2LINE "" OFF)
 option(CPPTRACE_GET_SYMBOLS_WITH_DBGHELP "" OFF)
 option(CPPTRACE_GET_SYMBOLS_WITH_NOTHING "" OFF)
 
+option(CPPTRACE_UNWIND_WITH_UNWIND "" OFF)
 option(CPPTRACE_UNWIND_WITH_EXECINFO "" OFF)
 option(CPPTRACE_UNWIND_WITH_WINAPI "" OFF)
 option(CPPTRACE_UNWIND_WITH_NOTHING "" OFF)
@@ -100,6 +101,7 @@ function(check_support var source includes libraries definitions)
   set(${var} ${${var}} PARENT_SCOPE)
 endfunction()
 
+check_support(HAS_UNWIND has_unwind.cpp "" "" "")
 check_support(HAS_EXECINFO has_execinfo.cpp "" "" "")
 check_support(HAS_BACKTRACE has_backtrace.cpp "" "backtrace" "${CPPTRACE_BACKTRACE_PATH_DEFINITION}")
 check_support(HAS_CXXABI has_cxxabi.cpp "" "" "")
@@ -121,6 +123,7 @@ if(
     CPPTRACE_GET_SYMBOLS_WITH_ADDR2LINE OR
     CPPTRACE_GET_SYMBOLS_WITH_DBGHELP OR
     CPPTRACE_GET_SYMBOLS_WITH_NOTHING OR
+    CPPTRACE_UNWIND_WITH_UNWIND OR
     CPPTRACE_UNWIND_WITH_EXECINFO OR
     CPPTRACE_UNWIND_WITH_WINAPI OR
     CPPTRACE_UNWIND_WITH_NOTHING
@@ -142,6 +145,7 @@ if(
   NOT (
     CPPTRACE_FULL_TRACE_WITH_LIBBACKTRACE OR
     CPPTRACE_FULL_TRACE_WITH_STACKTRACE OR
+    CPPTRACE_UNWIND_WITH_UNWIND OR
     CPPTRACE_UNWIND_WITH_EXECINFO OR
     CPPTRACE_UNWIND_WITH_WINAPI OR
     CPPTRACE_UNWIND_WITH_NOTHING
@@ -149,12 +153,15 @@ if(
 )
   # Attempt to auto-config
   if(UNIX)
-    if(HAS_EXECINFO)
+    if(HAS_UNWIND)
+      set(CPPTRACE_UNWIND_WITH_UNWIND On)
+      message(STATUS "Cpptrace auto config: Using libgcc unwind for unwinding")
+    elseif(HAS_EXECINFO)
       set(CPPTRACE_UNWIND_WITH_EXECINFO On)
       message(STATUS "Cpptrace auto config: Using execinfo.h for unwinding")
     else()
       set(CPPTRACE_UNWIND_WITH_NOTHING On)
-      message(FATAL_ERROR "Cpptrace auto config: <execinfo.h> doesn't seem to be supported, stack tracing will not work. To compile anyway set CPPTRACE_UNWIND_WITH_NOTHING.")
+      message(FATAL_ERROR "Cpptrace auto config: No unwinding back-end seems to be supported, stack tracing will not work. To compile anyway set CPPTRACE_UNWIND_WITH_NOTHING.")
     endif()
   elseif(WIN32)
     set(CPPTRACE_UNWIND_WITH_WINAPI On)
@@ -266,6 +273,13 @@ if(CPPTRACE_GET_SYMBOLS_WITH_NOTHING)
 endif()
 
 # Unwinding
+if(CPPTRACE_UNWIND_WITH_UNWIND)
+  if(NOT HAS_UNWIND)
+    message(WARNING "Cpptrace: CPPTRACE_UNWIND_WITH_UNWIND specified but libgcc unwind doesn't seem to be available.")
+  endif()
+  target_compile_definitions(cpptrace PUBLIC CPPTRACE_UNWIND_WITH_UNWIND)
+endif()
+
 if(CPPTRACE_UNWIND_WITH_EXECINFO)
   if(NOT HAS_EXECINFO)
     message(WARNING "Cpptrace: CPPTRACE_UNWIND_WITH_EXECINFO specified but execinfo.h doesn't seem to be available.")

README.md

@@ -112,11 +112,12 @@ also manually set which back-end you want used.
 
 **Unwinding**
 
-| Library    | CMake config                    | Platforms      | Info                                                               |
+| Library       | CMake config                    | Platforms      | Info                                                                                                                                                                                               |
-| ---------- | ------------------------------- | -------------- | ------------------------------------------------------------------ |
+| ------------- | ------------------------------- | -------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| execinfo.h | `CPPTRACE_UNWIND_WITH_EXECINFO` | linux, macos   | Frames are captured with `execinfo.h`'s `backtrace`, part of libc. |
+| libgcc unwind | `CPPTRACE_UNWIND_WITH_UNWIND`   | linux, macos   | Frames are captured with libgcc's `_Unwind_Backtrace`, which currently produces the most accurate stack traces on gcc/clang. Libgcc is often linked by default, and llvm has something equivalent. |
-| winapi     | `CPPTRACE_UNWIND_WITH_WINAPI`   | windows, mingw | Frames are captured with `CaptureStackBackTrace`.                  |
+| execinfo.h    | `CPPTRACE_UNWIND_WITH_EXECINFO` | linux, macos   | Frames are captured with `execinfo.h`'s `backtrace`, part of libc.                                                                                                                                 |
-| N/A        | `CPPTRACE_UNWIND_WITH_NOTHING`  | all            | Unwinding is not done, stack traces will be empty.                 |
+| winapi        | `CPPTRACE_UNWIND_WITH_WINAPI`   | windows, mingw | Frames are captured with `CaptureStackBackTrace`.                                                                                                                                                  |
+| N/A           | `CPPTRACE_UNWIND_WITH_NOTHING`  | all            | Unwinding is not done, stack traces will be empty.                                                                                                                                                 |
 
 These back-ends require a fixed buffer has to be created to read addresses into while unwinding. By default the buffer
 can hold addresses for 100 frames (beyond the `skip` frames). This is configurable with `CPPTRACE_HARD_MAX_FRAMES`.

ci/build-in-all-configs.py

@@ -122,6 +122,7 @@ def main():
             "target": ["Debug"],
             "std": ["11", "20"],
             "unwind": [
+                "CPPTRACE_UNWIND_WITH_UNWIND",
                 "CPPTRACE_UNWIND_WITH_EXECINFO",
                 "CPPTRACE_UNWIND_WITH_NOTHING",
             ],
@@ -152,6 +153,7 @@ def main():
             "target": ["Debug"],
             "std": ["11", "20"],
             "unwind": [
+                "CPPTRACE_UNWIND_WITH_UNWIND",
                 "CPPTRACE_UNWIND_WITH_EXECINFO",
                 "CPPTRACE_UNWIND_WITH_NOTHING",
             ],

ci/test-all-configs.py

@@ -203,6 +203,7 @@ def main():
             "std": ["11", "20"],
             "unwind": [
                 "CPPTRACE_UNWIND_WITH_EXECINFO",
+                "CPPTRACE_UNWIND_WITH_UNWIND",
                 #"CPPTRACE_UNWIND_WITH_NOTHING",
             ],
             "symbols": [
@@ -233,6 +234,7 @@ def main():
             "std": ["11", "20"],
             "unwind": [
                 "CPPTRACE_UNWIND_WITH_EXECINFO",
+                "CPPTRACE_UNWIND_WITH_UNWIND",
                 #"CPPTRACE_UNWIND_WITH_NOTHING",
             ],
             "symbols": [

cmake/has_unwind.cpp

@@ -0,0 +1,14 @@
+#include <cstdint>
+
+#include <unwind.h>
+
+_Unwind_Reason_Code unwind_callback(_Unwind_Context* context, void* arg) {
+    _Unwind_GetIP(context);
+    int is_before_instruction = 0;
+    uintptr_t ip = _Unwind_GetIPInfo(context, &is_before_instruction);
+    return _URC_END_OF_STACK;
+}
+
+int main() {
+    _Unwind_Backtrace(unwind_callback, nullptr);
+}

lint.sh

@@ -4,7 +4,7 @@ status=0
 while read f
 do
     echo checking $f
-    flags="-DCPPTRACE_FULL_TRACE_WITH_LIBBACKTRACE -DCPPTRACE_FULL_TRACE_WITH_STACKTRACE -DCPPTRACE_GET_SYMBOLS_WITH_LIBBACKTRACE -DCPPTRACE_GET_SYMBOLS_WITH_LIBDL -DCPPTRACE_GET_SYMBOLS_WITH_ADDR2LINE -DCPPTRACE_GET_SYMBOLS_WITH_NOTHING -DCPPTRACE_UNWIND_WITH_EXECINFO -DCPPTRACE_UNWIND_WITH_NOTHING -DCPPTRACE_DEMANGLE_WITH_CXXABI -DCPPTRACE_DEMANGLE_WITH_NOTHING"
+    flags="-DCPPTRACE_FULL_TRACE_WITH_LIBBACKTRACE -DCPPTRACE_FULL_TRACE_WITH_STACKTRACE -DCPPTRACE_GET_SYMBOLS_WITH_LIBBACKTRACE -DCPPTRACE_GET_SYMBOLS_WITH_LIBDL -DCPPTRACE_GET_SYMBOLS_WITH_ADDR2LINE -DCPPTRACE_GET_SYMBOLS_WITH_NOTHING -DCPPTRACE_UNWIND_WITH_EXECINFO -DCPPTRACE_UNWIND_WITH_UNWIND -DCPPTRACE_UNWIND_WITH_NOTHING -DCPPTRACE_DEMANGLE_WITH_CXXABI -DCPPTRACE_DEMANGLE_WITH_NOTHING"
     clang-tidy $f -- -std=c++11 -Iinclude $@ $flags
     ret=$?
     if [ $ret -ne 0 ]; then

src/unwind/unwind_with_unwind.cpp

@@ -0,0 +1,58 @@
+#ifdef CPPTRACE_UNWIND_WITH_UNWIND
+
+#include "cpptrace_unwind.hpp"
+#include "../platform/cpptrace_common.hpp"
+
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <vector>
+
+#include <unwind.h>
+
+namespace cpptrace {
+    namespace detail {
+        struct unwind_state {
+            std::size_t skip;
+            std::size_t count;
+            std::vector<void*>& vec;
+        };
+
+        _Unwind_Reason_Code unwind_callback(_Unwind_Context* context, void* arg) {
+            unwind_state& state = *static_cast<unwind_state*>(arg);
+            if(state.skip) {
+                state.skip--;
+                if(_Unwind_GetIP(context) == uintptr_t(0)) {
+                    return _URC_END_OF_STACK;
+                } else {
+                    return _URC_NO_REASON;
+                }
+            }
+
+            assert(state.count < state.vec.size());
+            int is_before_instruction = 0;
+            uintptr_t ip = _Unwind_GetIPInfo(context, &is_before_instruction);
+            if(!is_before_instruction && ip != uintptr_t(0)) {
+                ip--;
+            }
+            if (ip == uintptr_t(0) || state.count == state.vec.size()) {
+                return _URC_END_OF_STACK;
+            } else {
+                state.vec[state.count++] = (void*)ip;
+                return _URC_NO_REASON;
+            }
+        }
+
+        CPPTRACE_FORCE_NO_INLINE
+        std::vector<void*> capture_frames(size_t skip) {
+            std::vector<void*> frames(hard_max_frames, nullptr);
+            unwind_state state{skip + 1, 0, frames};
+            _Unwind_Backtrace(unwind_callback, &state);
+            frames.resize(state.count);
+            frames.shrink_to_fit();
+            return frames;
+        }
+    }
+}
+
+#endif