Merge bitcoin-core/secp256k1#1750: ci: Use clang-snapshot in "MSan" job

53585f93b7 ci: Use clang-snapshot in "MSan" job (Hennadii Stepanov)
6894c964f3 Fix Clang 21+ `-Wuninitialized-const-pointer` warning when using MSan (Hennadii Stepanov)

Pull request description:

  In Bitcoin Core, the "MSan" CI jobs use the latest tagged Clang available from http://apt.llvm.org.

  This PR applies similar changes and switches the "MSan" CI jobs to clang-snapshot.

  This exposes problematic code that was reported in https://github.com/bitcoin/bitcoin/issues/33284.

ACKs for top commit:
  real-or-random:
    utACK 53585f93b7

Tree-SHA512: 79bc10f1d0a60ed67b518eb8fab9a48146a4ef1fff95c8775717be3a950b323ae89a12999504ed8446f164da426894abe02f9fb61b5ca19453d549a34873b73b

.github/workflows/ci.yml

@@ -417,6 +417,9 @@ jobs:
               # when ctime_tests when enabled.
               CFLAGS: '-fsanitize=memory -fsanitize-recover=memory -fsanitize-memory-param-retval -g'
               CTIMETESTS: 'no'
+        cc:
+          - 'clang'
+          - 'clang-snapshot'
 
     env:
       ECDH: 'yes'
@@ -425,7 +428,7 @@ jobs:
       SCHNORRSIG: 'yes'
       MUSIG: 'yes'
       ELLSWIFT: 'yes'
-      CC: 'clang'
+      CC: ${{ matrix.cc }}
       SECP256K1_TEST_ITERS: 32
       ASM: 'no'
       WITH_VALGRIND: 'no'

ci/linux-debian.Dockerfile

@@ -71,7 +71,7 @@ RUN \
     # Determine the version number of the LLVM development branch
     LLVM_VERSION=$(apt-cache search --names-only '^clang-[0-9]+$' | sort -V | tail -1 | cut -f1 -d" " | cut -f2 -d"-" ) && \
     # Install
-    DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y "clang-${LLVM_VERSION}" && \
+    DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y "clang-${LLVM_VERSION}" "libclang-rt-${LLVM_VERSION}-dev" && \
     # Create symlink
     ln -s "/usr/bin/clang-${LLVM_VERSION}" /usr/bin/clang-snapshot && \
     # Clean up

src/checkmem.h

@@ -48,7 +48,17 @@
 #  if __has_feature(memory_sanitizer)
 #    include <sanitizer/msan_interface.h>
 #    define SECP256K1_CHECKMEM_ENABLED 1
+#    if defined(__clang__) && ((__clang_major__ == 21 && __clang_minor__ >= 1) || __clang_major__ >= 22)
+#      define SECP256K1_CHECKMEM_UNDEFINE(p, len) do { \
+         /* Work around https://github.com/llvm/llvm-project/issues/160094 */ \
+         _Pragma("clang diagnostic push") \
+         _Pragma("clang diagnostic ignored \"-Wuninitialized-const-pointer\"") \
+         __msan_allocated_memory((p), (len)); \
+         _Pragma("clang diagnostic pop") \
+         } while(0)
+#    else
 #      define SECP256K1_CHECKMEM_UNDEFINE(p, len) __msan_allocated_memory((p), (len))
+#    endif
 #    define SECP256K1_CHECKMEM_DEFINE(p, len) __msan_unpoison((p), (len))
 #    define SECP256K1_CHECKMEM_MSAN_DEFINE(p, len) __msan_unpoison((p), (len))
 #    define SECP256K1_CHECKMEM_CHECK(p, len) __msan_check_mem_is_initialized((p), (len))