crypto: disable ASan instrumentation of SSE4 SHA256 for GCC
What the developer wrote
Authored by deadmanoz
crypto: disable ASan instrumentation of SSE4 SHA256 for GCC
The existing Clang-only no_sanitize("address") guard is extended to
also cover GCC. When GCC compiles this file with -fsanitize=address
in debug builds, the instrumented inline assembly causes a SEGV during
SHA256AutoDetect()'s self-test on CPUs that use the SSE4 code path
(i.e. those without SHA-NI support), regardless of optimization level.
The original Clang code placed the attribute between the function
declarator and the opening brace. GCC's Attribute Syntax
documentation notes that this position in a function definition
"may, in future, be permitted," so it is not currently supported.
The attribute is moved to the start of the function definition,
which is valid form for both GCC and Clang.
The preprocessor guards are restructured so each compiler branch is
explicit: __clang__ with __has_feature, and __GNUC__ with
__SANITIZE_ADDRESS__.
What changed, and why it matters
This is a build-compatibility fix, not a security vulnerability in normal Bitcoin operation. It stops a specific compiler sanitizer (GCC's AddressSanitizer, used only in debug/test builds) from crashing when running SHA-256 self-tests on older CPUs that lack SHA-NI hardware support. The change does not affect production releases or how Bitcoin validates transactions.
No urgent action needed. Treat as a normal build/test fix. Ensure CI debug builds with GCC ASan on non-SHA-NI hardware or emulators pass SHA256 self-tests after applying the patch.
Security signals we found
Compiler sanitizer incompatibility with inline assembly
SIGSEGV during cryptographic self-test under debug build configuration
Conditional CPU code path (SSE4 vs SHA-NI) involved in failure
No change to cryptographic algorithm or runtime validation logic
Evidence from the diff
The commit moves and broadens an existing attribute((no_sanitize(“address”))) annotation on sha256_sse4::Transform so it also applies to GCC, not just Clang. Without the attribute, GCC’s ASan-instrumented inline assembly in this file causes a SIGSEGV during SHA256AutoDetect()’s self-test on the SSE4 code path. The fix restructures preprocessor checks to use SANITIZE_ADDRESS for GCC and __has_feature(address_sanitizer) for Clang, and places the attribute at the start of the function definition because GCC does not support it between the declarator and the opening brace.
Changed components
src/crypto/sha256_sse4.cppGCC + AddressSanitizer debug buildsSHA256AutoDetect() SSE4 self-test pathInspect captured patch +14 / −9
diff --git a/src/crypto/sha256_sse4.cpp b/src/crypto/sha256_sse4.cpp
index 2d37d124..4464ec92 100644
--- a/src/crypto/sha256_sse4.cpp
+++ b/src/crypto/sha256_sse4.cpp
@@ -12,18 +12,23 @@
namespace sha256_sse4
{
-void Transform(uint32_t* s, const unsigned char* chunk, size_t blocks)
-#if defined(__clang__)
- /*
- clang is unable to compile this with -O0 and -fsanitize=address.
- See upstream bug: https://github.com/llvm/llvm-project/issues/92182.
- This also fails to compile with -O2, -fcf-protection & -fsanitize=address.
- See https://github.com/bitcoin/bitcoin/issues/31913.
- */
-#if __has_feature(address_sanitizer)
+/*
+Both Clang and GCC fail with ASan on this inline assembly:
+- Clang: compile failure with -O0 or -O2 + -fcf-protection under ASan.
+ See https://github.com/llvm/llvm-project/issues/92182
+ and https://github.com/bitcoin/bitcoin/issues/31913.
+- GCC: runtime SEGV during SHA256AutoDetect()'s self-test under ASan,
+ regardless of optimization level.
+ See https://github.com/bitcoin/bitcoin/issues/34881.
+*/
+#if defined(__SANITIZE_ADDRESS__)
+ __attribute__((no_sanitize("address")))
+#elif defined(__clang__)
+#if __has_feature(address_sanitizer) // fallback can be removed once support for Clang 21 is dropped
__attribute__((no_sanitize("address")))
#endif
#endif
+void Transform(uint32_t* s, const unsigned char* chunk, size_t blocks)
{
static const uint32_t K256 alignas(16) [] = {
0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
Why this scored 18/100
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