fix: remove C++ exception ABI from vendored libunwind build. (#1544)

Author: supervacuus

CHANGELOG.md

@@ -9,6 +9,7 @@
 **Fixes**:
 
 - Fix use-after-free on allocation failure when merging scope tags, extra, and contexts into a captured event. ([#1539](https://github.com/getsentry/sentry-native/pull/1539))
+- Remove C++ exception ABI symbols (`_Unwind_Resume`, etc.) from vendored `libunwind` build. ([#1544](https://github.com/getsentry/sentry-native/pull/1544))
 
 ## 0.13.0
 

vendor/libunwind/CMakeLists.txt

@@ -39,9 +39,6 @@ set(UNWIND_COMMON_SOURCES
 
 # Local sources (libunwind_la_SOURCES_local_nounwind + os_local)
 set(UNWIND_LOCAL_SOURCES
-    # os_linux_local (CXX exceptions support - _ReadULEB/_ReadSLEB)
-    ${LIBUNWIND_SRC}/mi/_ReadULEB.c
-    ${LIBUNWIND_SRC}/mi/_ReadSLEB.c
     # local nounwind
     ${LIBUNWIND_SRC}/mi/backtrace.c
     ${LIBUNWIND_SRC}/mi/dyn-cancel.c
@@ -64,25 +61,10 @@ set(UNWIND_LOCAL_SOURCES
     ${LIBUNWIND_SRC}/mi/Lset_iterate_phdr_function.c
     ${LIBUNWIND_SRC}/mi/Lset_reg.c
     ${LIBUNWIND_SRC}/mi/Lget_elf_filename.c
-    # local unwind (CXX exception support)
-    ${LIBUNWIND_SRC}/unwind/Backtrace.c
-    ${LIBUNWIND_SRC}/unwind/DeleteException.c
-    ${LIBUNWIND_SRC}/unwind/FindEnclosingFunction.c
-    ${LIBUNWIND_SRC}/unwind/ForcedUnwind.c
-    ${LIBUNWIND_SRC}/unwind/GetBSP.c
-    ${LIBUNWIND_SRC}/unwind/GetCFA.c
-    ${LIBUNWIND_SRC}/unwind/GetDataRelBase.c
-    ${LIBUNWIND_SRC}/unwind/GetGR.c
-    ${LIBUNWIND_SRC}/unwind/GetIP.c
-    ${LIBUNWIND_SRC}/unwind/GetIPInfo.c
-    ${LIBUNWIND_SRC}/unwind/GetLanguageSpecificData.c
-    ${LIBUNWIND_SRC}/unwind/GetRegionStart.c
-    ${LIBUNWIND_SRC}/unwind/GetTextRelBase.c
-    ${LIBUNWIND_SRC}/unwind/RaiseException.c
-    ${LIBUNWIND_SRC}/unwind/Resume.c
-    ${LIBUNWIND_SRC}/unwind/Resume_or_Rethrow.c
-    ${LIBUNWIND_SRC}/unwind/SetGR.c
-    ${LIBUNWIND_SRC}/unwind/SetIP.c
+    # NOTE: The src/unwind/ sources (C++ exception ABI: _Unwind_Resume,
+    # _Unwind_RaiseException, etc.) are intentionally excluded. They conflict
+    # with libgcc_eh.a when linking with -static-libgcc, and sentry-native
+    # only needs the local unwinding API (_UL*_init_local, _UL*_step, etc.).
 )
 
 # DWARF sources (local)

vendor/libunwind/VENDORING.md

@@ -20,9 +20,12 @@ Linux without requiring users to install any external packages.  Only the
 | x86 (i686, 32-bit) | `src/x86/`     | `include/tdep-x86/`     |
 | aarch64            | `src/aarch64/` | `include/tdep-aarch64/` |
 
-Core shared code: `src/mi/`, `src/dwarf/`, `src/unwind/`, `src/os-linux.c`,
+Core shared code: `src/mi/`, `src/dwarf/`, `src/os-linux.c`,
 `src/dl-iterate-phdr.c`.
 
+> **Note:** `src/unwind/` is present in the tree but is **not compiled**. See
+> [Excluded: C++ exception ABI sources](#excluded-c-exception-abi-sources) below.
+
 ## What Was Removed from the Release Tarball
 
 The release tarball contains 911 files.  547 were removed (the vendor tree
@@ -81,9 +84,25 @@ custom `CMakeLists.txt`:
 |----------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------|
 | `src/arm/`, `include/tdep-arm/`                                                                          | ARM 32-bit — kept for potential future use                                                                                                 |
 | `src/riscv/`, `include/tdep-riscv/`                                                                      | RISC-V — kept for potential future use                                                                                                     |
+| `src/unwind/`, `src/mi/_ReadULEB.c`, `src/mi/_ReadSLEB.c`                                                | C++ exception ABI conflicts with `libgcc_eh.a`; see [above](#excluded-c-exception-abi-sources)                                             |
 | `include/libunwind-*.h` for removed arches                                                               | Referenced via `#ifdef` in `include/libunwind.h` — harmless dead code                                                                      |
 | Autotools artifacts (`configure`, `configure.ac`, `Makefile.am`, `Makefile.in`, `aclocal.m4`, `INSTALL`) | Carried over from the release tarball. Not used by CMake, but `configure.ac` and `Makefile.am` are useful as reference for the build logic |
 
+### Excluded: C++ exception ABI sources
+
+The `src/unwind/` directory and `src/mi/_ReadULEB.c` / `src/mi/_ReadSLEB.c`
+are **present in the tree but excluded from the CMake build**.  These files
+implement the Itanium C++ exception handling ABI (`_Unwind_Resume`,
+`_Unwind_RaiseException`, `_Unwind_ForcedUnwind`, etc.) — the same symbols
+that `libgcc_eh.a` provides.
+
+When sentry-native is built as a static library (`SENTRY_BUILD_SHARED_LIBS=OFF`)
+and linked into a shared library whose toolchain uses `-static-libgcc`
+(e.g. godot-cpp), including these symbols causes **multiple definition** errors
+against `libgcc_eh.a`.  Excluding them is safe because sentry-native only uses
+the local unwinding API (`_ULx86_64_init_local`, `_ULx86_64_step`, etc.) and
+never calls into the C++ exception ABI.
+
 ## Custom Additions (not in the upstream tarball)
 
 | File                                | Purpose                                                                                                                                           |
@@ -123,6 +142,8 @@ both GCC and Clang.
    removed architecture dirs listed above:
    - `src/` — keep only: `aarch64/`, `arm/`, `dwarf/`, `mi/`, `riscv/`,
      `unwind/`, `x86/`, `x86_64/`, and top-level `.c` / `.h` files
+     (`src/unwind/` is kept for reference but **not compiled** — do not add it
+     to `CMakeLists.txt`)
    - `include/` — keep only: `tdep/`, `tdep-aarch64/`, `tdep-arm/`,
      `tdep-riscv/`, `tdep-x86/`, `tdep-x86_64/`, and all top-level `.h` /
      `.h.in` files