[newlib-cygwin] Cygwin: signal: Clear direction flag in sigdeleyed

[Takashi Yano]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=bb2a8a8cb3ae8753dd275caffdef567f3c2da1b6

commit bb2a8a8cb3ae8753dd275caffdef567f3c2da1b6
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Mon Mar 24 09:26:34 2025 +0900

    Cygwin: signal: Clear direction flag in sigdeleyed
    
    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: Corinna Vischen <corinna@vinschen.de>
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

Diff:
---
 winsup/cygwin/release/3.6.1  | 3 +++
 winsup/cygwin/scripts/gendef | 1 +
 2 files changed, 4 insertions(+)

diff --git a/winsup/cygwin/release/3.6.1 b/winsup/cygwin/release/3.6.1
index 0b54b5fd3..0b05f4550 100644
--- a/winsup/cygwin/release/3.6.1
+++ b/winsup/cygwin/release/3.6.1
@@ -3,3 +3,6 @@ Fixes:
 
 - Console mode is really restored to the previous mode.
   Addresses: https://github.com/msys2/msys2-runtime/issues/268
+
+- Clear direction flag in sigdeleyed before calling signal handler.
+  Addresses: https://cygwin.com/pipermail/cygwin/2025-March/257704.html
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