[compiler-rt] aee4f2b - [libFuzzer] always install signal handler with SA_ONSTACK (#147422)

[via llvm-commits]

Author: Keith Randall
Date: 2025-08-09T11:45:41-07:00
New Revision: aee4f2baccdbc018d0ac60eaa4e2a0a5f30bcdf5

URL: https://github.com/llvm/llvm-project/commit/aee4f2baccdbc018d0ac60eaa4e2a0a5f30bcdf5
DIFF: https://github.com/llvm/llvm-project/commit/aee4f2baccdbc018d0ac60eaa4e2a0a5f30bcdf5.diff

LOG: [libFuzzer] always install signal handler with SA_ONSTACK (#147422)

SA_ONSTACK is required for certain runtimes that use small stacks, for
instance the Go runtime.
See https://github.com/golang/go/issues/49075
SA_ONSTACK is a no-op unless someone also calls sigaltstack.

Added: 
    

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

Removed: 
    


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diff  --git a/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
index ae22ecf108420..b1bb1387876e0 100644
--- a/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
@@ -78,10 +78,14 @@ static void SetSigaction(int signum,
   }
 
   struct sigaction new_sigact = {};
-  // 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);
+  // 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;
   new_sigact.sa_sigaction = callback;
   if (sigaction(signum, &new_sigact, nullptr)) {
     Printf("libFuzzer: sigaction failed with %d\n", errno);