[PATCH] Cygwin: signal: Clear direction flag in sigdeleyed

[Corinna Vinschen]

On Mar 24 10:28, Takashi Yano wrote:
> 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.Franke@t-online.de>
> Reviewed-by:
> Signed-off-by: Takashi Yano <takashi.yano@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

GTG, of course!


Thanks,
Corinna