From e37a53a2fc9faa944aa3a224cf942d0c89bf9414 Mon Sep 17 00:00:00 2001
From: Patrick Rudolph <patrick.rudolph@9elements.com>
Date: Sat, 16 Aug 2025 09:21:25 +0200
Subject: [PATCH] arch/x86/memcpy: Fix undefined behaviour

Clear DF flag before invoking MOVS instruction to make sure it
increments %esi/%edi on each mov.

Change-Id: I209f50dec2003ea9846e5958d3e77b8979f338df
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/88796
Reviewed-by: Shuo Liu <shuo.liu@intel.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
---
 src/arch/x86/memcpy.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/arch/x86/memcpy.c b/src/arch/x86/memcpy.c
index 9da2a7512e..3b5a64d163 100644
--- a/src/arch/x86/memcpy.c
+++ b/src/arch/x86/memcpy.c
@@ -16,6 +16,7 @@ void *memcpy(void *dest, const void *src, size_t n)
 
 #if ENV_X86_64
 	asm volatile(
+		"cld\n\t"
 		"rep ; movsq\n\t"
 		"mov %4,%%rcx\n\t"
 		"rep ; movsb\n\t"
@@ -25,6 +26,7 @@ void *memcpy(void *dest, const void *src, size_t n)
 	);
 #else
 	asm volatile(
+		"cld\n\t"
 		"rep ; movsl\n\t"
 		"movl %4,%%ecx\n\t"
 		"rep ; movsb\n\t"