[SanitizerCoverage] -fsanitize-coverage-allowlist removes all coverage (clang 18.1.7 Linux prebuilt)

[0xLucifer]

Bug Report (LLVM)

Title: [SanitizerCoverage] -fsanitize-coverage-allowlist removes all coverage (clang 18.1.7 Linux prebuilt)

Env

• clang+llvm-18.1.7-x86_64-linux-gnu-ubuntu-18.04.tar.xz (https://github.com/llvm/llvm-project/releases/download/llvmorg-18.1.7/clang+llvm-18.1.7-x86_64-linux-gnu-ubuntu-18.04.tar.xz)
• OS: Ubuntu 22.04.4 LTS
• Target: x86_64-unknown-linux-gnu

Repro

// t.c
int main() { return 0; }

# allow.txt
src:.*t\.c

./llvm-18.1.7/bin/clang -fsanitize-coverage=trace-pc-guard -fsanitize-coverage-allowlist=allow.txt t.c -o t
gdb --nx --batch --eval-command="disassemble main" ./t | grep trace_pc_guard

Expected: main contains calls to __sanitizer_cov_trace_pc_guard.

Actual: No coverage calls. If the allowlist flag is removed, coverage appears.

[0xLucifer]

I’ve tried multiple LLVM versions and none of them could make the -fsanitize-coverage-allowlist mechanism work correctly, while using the trace-pc-guard coverage mode alone works fine. This issue is very frustrating.