After the commit f305ca916ad2, some stress-ng tests fail in arm64 windows. There seems to be two causes for this issue. One is that calling SuspendThread(GetCurrentThread()) may suspend myself in the kernel. Branching to sigdelayed in the kernel code does not work as expected as the original _cygtls::interrup_now() intended. The other cause is, single step exception sometimes does not trigger exception::handle() for some reason. Therefore, register vectored exception handler (VEH) and use it for single step exception instead.
Addresses: https://cygwin.com/pipermail/cygwin/2025-June/258332.html Fixes: f305ca916ad2 ("Cygwin: signal: Prevent unexpected crash on frequent SIGSEGV") Reported-by: Jeremy Drake <[email protected]> Reviewed-by: Signed-off-by: Takashi Yano <[email protected]> --- winsup/cygwin/exceptions.cc | 46 +++++++++++++++------------ winsup/cygwin/local_includes/cygtls.h | 1 + 2 files changed, 27 insertions(+), 20 deletions(-) diff --git a/winsup/cygwin/exceptions.cc b/winsup/cygwin/exceptions.cc index a4699b172..e5193551b 100644 --- a/winsup/cygwin/exceptions.cc +++ b/winsup/cygwin/exceptions.cc @@ -653,13 +653,6 @@ exception::handle (EXCEPTION_RECORD *e, exception_list *frame, CONTEXT *in, static int NO_COPY debugging = 0; _cygtls& me = _my_tls; - if (me.suspend_on_exception) - { - SuspendThread (GetCurrentThread ()); - if (e->ExceptionCode == (DWORD) STATUS_SINGLE_STEP) - return ExceptionContinueExecution; - } - if (debugging && ++debugging < 500000) { SetThreadPriority (hMainThread, THREAD_PRIORITY_NORMAL); @@ -923,6 +916,22 @@ sig_handle_tty_stop (int sig, siginfo_t *, void *) } } /* end extern "C" */ +static HANDLE h_veh = NULL; +static LONG CALLBACK +veh (EXCEPTION_POINTERS *ep) +{ + if (_my_tls.suspend_on_exception) + { + _my_tls.in_exception_handler = true; + while (_my_tls.suspend_on_exception) ; /* Don't call yield() to privent + the thread form being suspended + in the kernel. */ + if (ep->ExceptionRecord->ExceptionCode == (DWORD) STATUS_SINGLE_STEP) + return EXCEPTION_CONTINUE_EXECUTION; + } + return EXCEPTION_CONTINUE_SEARCH; +} + bool _cygtls::interrupt_now (CONTEXT *cx, siginfo_t& si, void *handler, struct sigaction& siga) @@ -943,25 +952,22 @@ _cygtls::interrupt_now (CONTEXT *cx, siginfo_t& si, void *handler, by setting the trap flag (TF) before calling ResumeThread(). This will trigger either STATUS_SINGLE_STEP or the exception caused by the instruction that Rip originally pointed to. By suspending the - targeted thread within exception::handle(), Rip no longer points - to the problematic instruction, allowing safe handling of the - interrupt. As a result, Rip can be adjusted appropriately, and the - thread can resume execution without unexpected crashes. */ + targeted thread within the vectored exception handler veh(), Rip no + longer points to the problematic instruction, allowing safe handling + of the interrupt. As a result, Rip can be adjusted appropriately, + and the thread can resume execution without unexpected crashes. */ if (!inside_kernel (cx, true)) { + if (h_veh == NULL) + h_veh = AddVectoredExceptionHandler (1, veh); cx->EFlags |= 0x100; /* Set TF (setup single step execution) */ SetThreadContext (*this, cx); suspend_on_exception = true; + in_exception_handler = false; ResumeThread (*this); - ULONG cnt = 0; - NTSTATUS status; - do - { - yield (); - status = NtQueryInformationThread (*this, ThreadSuspendCount, - &cnt, sizeof (cnt), NULL); - } - while (NT_SUCCESS (status) && cnt == 0); + while (!in_exception_handler) + yield (); + SuspendThread (*this); GetThreadContext (*this, cx); suspend_on_exception = false; } diff --git a/winsup/cygwin/local_includes/cygtls.h b/winsup/cygwin/local_includes/cygtls.h index 44bd44e72..05ac5627d 100644 --- a/winsup/cygwin/local_includes/cygtls.h +++ b/winsup/cygwin/local_includes/cygtls.h @@ -204,6 +204,7 @@ public: /* Do NOT remove this public: line, it's a marker for gentls_offsets. */ __tlsstack_t stack[TLS_STACK_SIZE]; unsigned initialized; volatile bool suspend_on_exception; + volatile bool in_exception_handler; public: /* Do NOT remove this public: line, it's a marker for gentls_offsets. */ void init_thread (void *, DWORD (*) (void *, void *)); -- 2.45.1
