linux-toradex.git/tools/objtool/tests/generic/fixtures/ubsan_noise.c, branch master Linux kernel for Apalis and Colibri modules objtool/klp: Add test for UBSAN metadata in an unchanged function 2026-09-21T09:12:08+00:00 Song Liu song@kernel.org 2026-09-16T18:43:49+00:00 41ca5150dd816f856c545775525013513e9a31fa Every instrumented operation gets a per-callsite metadata object in an anonymous data section -- .data..Lubsan_data and .data..Lubsan_type from GCC, .data..L__unnamed_ from Clang -- whose names are compiler-generated and mean nothing across a rebuild. is_uncorrelated_section() exists so klp diff does not try to pair them up, and nothing tested it. The failure it prevents is a false positive, which is the direction this suite has least coverage of. Metadata belonging to a function nobody touched compares as different and drags that function into the patch. That is not a build failure: it is a larger livepatch than intended, pulling in dependencies with it, and every extra function is one more that can fail to correlate or to apply. The fixture is built with -fsanitize=shift, which both compilers instrument; neither emits a bounds check for an index it can prove in range. One function changes, the other is byte-identical and carries instrumentation of its own, and the test asserts the second is left alone. Verified by removing each rule from is_uncorrelated_section() in turn, which splits neatly by toolchain: dropping the .data..Lubsan rule fails the test under gcc, dropping .data..L__unnamed_ fails it under clang. One test, two code paths, each checked by the compiler that reaches it. Assisted-by: Claude:claude-opus-4 Based-on-test-by: Joe Lawrence <joe.lawrence@redhat.com> Assisted-by: Claude:claude-opus-5 Signed-off-by: Song Liu <song@kernel.org> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://patch.msgid.link/20260916184351.2720310-57-song@kernel.org 
Every instrumented operation gets a per-callsite metadata object in an
anonymous data section -- .data..Lubsan_data and .data..Lubsan_type from
GCC, .data..L__unnamed_ from Clang -- whose names are compiler-generated
and mean nothing across a rebuild.  is_uncorrelated_section() exists so klp
diff does not try to pair them up, and nothing tested it.

The failure it prevents is a false positive, which is the direction this
suite has least coverage of.  Metadata belonging to a function nobody
touched compares as different and drags that function into the patch.  That
is not a build failure: it is a larger livepatch than intended, pulling in
dependencies with it, and every extra function is one more that can fail to
correlate or to apply.

The fixture is built with -fsanitize=shift, which both compilers
instrument; neither emits a bounds check for an index it can prove in
range.  One function changes, the other is byte-identical and carries
instrumentation of its own, and the test asserts the second is left alone.

Verified by removing each rule from is_uncorrelated_section() in turn,
which splits neatly by toolchain: dropping the .data..Lubsan rule fails the
test under gcc, dropping .data..L__unnamed_ fails it under clang.  One
test, two code paths, each checked by the compiler that reaches it.

Assisted-by: Claude:claude-opus-4
Based-on-test-by: Joe Lawrence <joe.lawrence@redhat.com>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20260916184351.2720310-57-song@kernel.org