From dd30acdd590f6a39a5d3c4a38e3d949e73b5e2fa Mon Sep 17 00:00:00 2001 From: Mathias Krause Date: Sat, 31 Mar 2012 17:23:53 +0200 Subject: [PATCH] Fix issues with x86 memcpy The x86 memcpy() implementation did not mention its implicit output registers ESI, EDI and ECX which might make this code miscompile when the compiler uses the value of EDI for the return value *after* the 'rep movsb' has completed. That would break the API of memcpy as this would return 'dst+len' instead of 'dst'. Fix this possible bug by removing the wrong comment and listing all output registers as such (using dummy stack variables that get optimized away). Also the leading 'cld' is superflous as the ABI mandates the direction flag to be cleared all the time when we're in C (see ) and we have no ASM call sites that might require it to be cleared explicitly (SMM might come to mind, but it clears the DF itself before passing control to the C part of the SMI handler). Last but not least fix the prototype to match the one from . Change-Id: I106422d41180c4ed876078cabb26b45e49f3fa93 Signed-off-by: Mathias Krause Reviewed-on: http://review.coreboot.org/836 Tested-by: build bot (Jenkins) Reviewed-by: Peter Stuge --- src/arch/x86/lib/memcpy.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/src/arch/x86/lib/memcpy.c b/src/arch/x86/lib/memcpy.c index de210928a..f8607cfc5 100644 --- a/src/arch/x86/lib/memcpy.c +++ b/src/arch/x86/lib/memcpy.c @@ -1,13 +1,15 @@ #include -void *memcpy(void *__restrict __dest, - __const void *__restrict __src, size_t __n) +void *memcpy(void *dest, const void *src, size_t n) { - asm("cld\n" - "rep\n" - "movsb" - : /* no input (?) */ - :"S"(__src), "D"(__dest), "c"(__n) - ); - return __dest; + unsigned long d0, d1, d2; + + asm volatile( + "rep movsb" + : "=S"(d0), "=D"(d1), "=c"(d2) + : "0"(src), "1"(dest), "2"(n) + : "memory" + ); + + return dest; } -- 2.25.1