[libFuzzer] Fix incorrect coverage number in fork mode

[yescallop]

Closes #82307.

I built LLVM with the changes and tested fuzzing in fork mode. The coverage number was correct:

[ye@ye-arch ~]$ /home/ye/work/llvm-project/build/bin/clang++ -fsanitize=fuzzer test_fuzzer.cc
[ye@ye-arch ~]$ ./a.out corpus -fork=4
INFO: Running with entropic power schedule (0xFF, 100).
INFO: Seed: 3152497917
INFO: Loaded 1 modules   (40 inline 8-bit counters): 40 [0x5aa6f7b310d0, 0x5aa6f7b310f8), 
INFO: Loaded 1 PC tables (40 PCs): 40 [0x5aa6f7b310f8,0x5aa6f7b31378), 
INFO: -fork=4: fuzzing in separate process(s)
INFO: -fork=4: 56 seed inputs, starting to fuzz in /tmp/libFuzzerTemp.FuzzWithFork54465.dir
#600649: cov: 36 ft: 224 corp: 56 exec/s: 300324 oom/timeout/crash: 0/0/0 time: 2s job: 1 dft_time: 0
#1548208: cov: 36 ft: 224 corp: 56 exec/s: 315853 oom/timeout/crash: 0/0/0 time: 3s job: 2 dft_time: 0
#2465991: cov: 36 ft: 224 corp: 56 exec/s: 229445 oom/timeout/crash: 0/0/0 time: 4s job: 3 dft_time: 0
#3887877: cov: 36 ft: 224 corp: 56 exec/s: 284377 oom/timeout/crash: 0/0/0 time: 5s job: 4 dft_time: 0

[github-actions]

Thank you for submitting a Pull Request (PR) to the LLVM Project!

This PR will be automatically labeled and the relevant teams will be
notified.

If you wish to, you can add reviewers by using the "Reviewers" section on this page.

If this is not working for you, it is probably because you do not have write
permissions for the repository. In which case you can instead tag reviewers by
name in a comment by using @ followed by their GitHub username.

If you have received no comments on your PR for a week, you can request a review
by "ping"ing the PR by adding a comment “Ping”. The common courtesy "ping" rate
is once a week. Please remember that you are asking for valuable time from other developers.

If you have further questions, they may be answered by the LLVM GitHub User Guide.

You can also ask questions in a comment on this PR, on the LLVM Discord or on the forums.

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Scallop Ye (yescallop)

Changes

Closes #82307.

I tried to build LLVM and test the changes but failed with the following error:

/usr/bin/ld: cannot find /home/ye/work/llvm-project/build/lib/clang/19/lib/linux/libclang_rt.fuzzer-x86_64.a: No such file or directory
/usr/bin/ld: cannot find /home/ye/work/llvm-project/build/lib/clang/19/lib/linux/libclang_rt.fuzzer_interceptors-x86_64.a: No such file or directory
/usr/bin/ld: cannot find /home/ye/work/llvm-project/build/lib/clang/19/lib/linux/libclang_rt.ubsan_standalone-x86_64.a: No such file or directory
/usr/bin/ld: cannot find /home/ye/work/llvm-project/build/lib/clang/19/lib/linux/libclang_rt.ubsan_standalone_cxx-x86_64.a: No such file or directory
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

I have no idea how to fix this. It'd be nice if you could help me with testing the changes.

---

Full diff: https://github.com/llvm/llvm-project/pull/82335.diff

1 Files Affected:

• (modified) compiler-rt/lib/fuzzer/FuzzerFork.cpp (+1-1)

diff --git a/compiler-rt/lib/fuzzer/FuzzerFork.cpp b/compiler-rt/lib/fuzzer/FuzzerFork.cpp
index c248a1d246a306..e544cd846e4db5 100644
--- a/compiler-rt/lib/fuzzer/FuzzerFork.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerFork.cpp
@@ -349,7 +349,7 @@ void FuzzWithFork(Random &Rand, const FuzzingOptions &Options,
                         &NewFeatures, Env.Cov, &NewCov, CFPath,
                         /*Verbose=*/false, /*IsSetCoverMerge=*/false);
     Env.Features.insert(NewFeatures.begin(), NewFeatures.end());
-    Env.Cov.insert(NewFeatures.begin(), NewFeatures.end());
+    Env.Cov.insert(NewCov.begin(), NewCov.end());
     RemoveFile(CFPath);
   }
 

[yescallop]

Ping

[renatahodovan]

The fix also works for me.