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[WTF] The signal handler runs on the alternate signal stack, and a thread that runs it there can be suspended #741

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[WTF] The signal handler runs on the alternate signal stack, and a thread that runs it there can be suspended #741

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[WTF] The signal handler runs on the alternate signal stack of a thre…
robobun Sep 28, 2026
5586daa
[WTF] A thread that runs the signal handler on the alternate stack ca…
robobun Sep 28, 2026
242085d
[WTF] Check the published registers against the thread's stack, and k…
robobun Sep 29, 2026
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7 changes: 7 additions & 0 deletions Source/WTF/wtf/threads/Signals.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -594,7 +594,14 @@ void SignalHandlers::finalize()
RELEASE_ASSERT(g_wtfConfig.isThreadSuspendResumeSignalConfigured);
result = sigdelset(&action.sa_mask, g_wtfConfig.sigThreadSuspendResume);
RELEASE_ASSERT(!result);
#if USE(BUN_JSC_ADDITIONS)
// On a thread that has an alternate signal stack, the handler runs on that stack. After a
// stack overflow the thread's own stack has no room for the signal frame: without this flag
// the kernel ends the process before this handler, or the one it chains to, can run.
action.sa_flags = SA_SIGINFO | SA_ONSTACK;
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#else
action.sa_flags = SA_SIGINFO;
#endif
auto systemSignals = toSystemSignal(signal);
result = sigaction(std::get<0>(systemSignals), &action, &handlers.oldActions[offsetForSystemSignal(std::get<0>(systemSignals))]);
if (std::get<1>(systemSignals))
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