[compiler-rt] 03372c7 - Revert "[libFuzzer] always install signal handler with SA_ONSTACK" (#153114)

[via llvm-commits]

Author: Keith Randall
Date: 2025-08-12T08:52:58-07:00
New Revision: 03372c7782e60f0c52dea39fbd5f87e19e306967

URL: https://github.com/llvm/llvm-project/commit/03372c7782e60f0c52dea39fbd5f87e19e306967
DIFF: https://github.com/llvm/llvm-project/commit/03372c7782e60f0c52dea39fbd5f87e19e306967.diff

LOG: Revert "[libFuzzer] always install signal handler with SA_ONSTACK" (#153114)

Reverts llvm/llvm-project#147422

Seems to be causing problems with tracebacks. Probably the trackback
code doesn't know how to switch back to the regular stack after it gets
to the top of the signal stack.

Added: 
    

Modified: 
    compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
index b1bb1387876e0..ae22ecf108420 100644
--- a/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
@@ -78,14 +78,10 @@ static void SetSigaction(int signum,
   }
 
   struct sigaction new_sigact = {};
-  // SA_ONSTACK is required for certain runtimes that use small stacks, for
-  // instance the Go runtime.
-  // See https://github.com/golang/go/issues/49075
-  // Address sanitizer also wants SA_ONSTACK, and the fuzzer and sanitizer
-  // often run together.
-  // SA_ONSTACK is a no-op unless someone also calls sigaltstack. That is left
-  // up to code that needs it.
-  new_sigact.sa_flags = SA_SIGINFO | SA_ONSTACK;
+  // Address sanitizer needs SA_ONSTACK (causing the signal handler to run on a
+  // dedicated stack) in order to be able to detect stack overflows; keep the
+  // flag if it's set.
+  new_sigact.sa_flags = SA_SIGINFO | (sigact.sa_flags & SA_ONSTACK);
   new_sigact.sa_sigaction = callback;
   if (sigaction(signum, &new_sigact, nullptr)) {
     Printf("libFuzzer: sigaction failed with %d\n", errno);