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fix(fuzz): link UBSan's C++ runtime into the fuzz binary

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The cbm-fuzz rule links through $(CC), the C driver. On Linux, clang's C
driver links UBSan's C runtime but leaves out its C++ part
(ubsan_standalone_cxx), while the C++ objects (preprocessor.cpp and the
vendored simplecpp) carry -fsanitize=vptr checks. The link failed with
undefined references to __ubsan_vptr_type_cache and
__ubsan_handle_dynamic_type_cache_miss, so the fuzz job has never built in
CI since it was added (dry runs 37212102899 and 38186491924).

-fsanitize-link-c++-runtime on the link line pulls that runtime in.

Checked in an ubuntu:24.04 arm64 container with CI's packages (clang 18,
llvm, libclang-rt-dev):
- a minimal reproduction (a C++ virtual call under -fsanitize=undefined,
  linked through clang) fails with exactly those two symbols without the
  flag, and links and runs with it;
- `make fuzz` links cbm-fuzz (lsp_all.o was compiled with -g0 added: the
  12.5 GB container ran out of memory on it with full debug info, which
  CI's runner does not);
- macOS Homebrew clang accepts the flag under -Werror.

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
This commit is contained in:
Martin Vogel
2026-10-12 06:31:53 +02:00
parent acf1cc2142
commit 738cfebb60
1 changed files with 5 additions and 1 deletions
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Makefile.cbm
+5 -1
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@@ -1601,8 +1601,12 @@ fuzz:
$(MAKE) -f Makefile.cbm build/fuzz/cbm-fuzz BUILD_DIR=build/fuzz \
CC=$(FUZZ_CC) CXX=$(FUZZ_CXX) SANITIZE="$(FUZZ_SANITIZE)"
# -fsanitize-link-c++-runtime: the link runs through the C driver, which on
# Linux leaves out UBSan's C++ runtime, but the C++ objects (preprocessor,
# simplecpp) carry -fsanitize=vptr checks that need it
# (__ubsan_vptr_type_cache, __ubsan_handle_dynamic_type_cache_miss).
$(BUILD_DIR)/cbm-fuzz: $(FUZZ_SRC) $(PROD_SRCS) $(EXTRACTION_SRCS) $(AC_LZ4_SRCS) $(ZSTD_SRCS) $(SQLITE_WRITER_SRC) $(OBJS_VENDORED_TEST) $(PROJECT_HDRS) | $(BUILD_DIR)
$(CC) $(CFLAGS_TEST) -fsanitize=fuzzer -o $@ \
$(CC) $(CFLAGS_TEST) -fsanitize=fuzzer -fsanitize-link-c++-runtime -o $@ \
$(FUZZ_SRC) $(PROD_SRCS) \
$(EXTRACTION_SRCS) $(AC_LZ4_SRCS) $(ZSTD_SRCS) $(SQLITE_WRITER_SRC) \
$(OBJS_VENDORED_TEST) \