x86_64 ABI requires the direction flag in CPU flags register cleared. https://learn.microsoft.com/en-us/cpp/build/x64-software-conventions However, currently that flag is not maintained in signal handler. Therefore, if the signal handler is called when that flag is set, it destroys the data and may crash if rep instruction is used in the signal handler. With this patch, the direction flag is cleared in sigdelayed() by adding cld instruction.
Addresses: https://cygwin.com/pipermail/cygwin/2025-March/257704.html Fixes: 1fd5e000ace5 ("import winsup-2000-02-17 snapshot") Reported-by: Christian Franke <christian.fra...@t-online.de> Reviewed-by: Signed-off-by: Takashi Yano <takashi.y...@nifty.ne.jp> --- winsup/cygwin/scripts/gendef | 1 + 1 file changed, 1 insertion(+) diff --git a/winsup/cygwin/scripts/gendef b/winsup/cygwin/scripts/gendef index a2f0392bc..861a2405b 100755 --- a/winsup/cygwin/scripts/gendef +++ b/winsup/cygwin/scripts/gendef @@ -179,6 +179,7 @@ sigdelayed: movq %rsp,%rbp pushf .seh_pushreg %rax # fake, there's no .seh_pushreg for the flags + cld # x86_64 ABI requires direction flag cleared # stack is aligned or unaligned on entry! # make sure it is aligned from here on # We could be called from an interrupted thread which doesn't know -- 2.45.1
