Mathias Krause (minipli@googlemail.com) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/836
-gerrit
commit ae57bd02ee4fd5636db10dd180f5d5c622d7e4ed Author: Mathias Krause minipli@googlemail.com Date: Sat Mar 31 17:23:53 2012 +0200
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 http://gcc.gnu.org/gcc-4.3/changes.html) 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 <string.h>.
Change-Id: I106422d41180c4ed876078cabb26b45e49f3fa93 Signed-off-by: Mathias Krause minipli@googlemail.com --- src/arch/x86/lib/memcpy.c | 20 +++++++++++--------- 1 files changed, 11 insertions(+), 9 deletions(-)
diff --git a/src/arch/x86/lib/memcpy.c b/src/arch/x86/lib/memcpy.c index de21092..f8607cf 100644 --- a/src/arch/x86/lib/memcpy.c +++ b/src/arch/x86/lib/memcpy.c @@ -1,13 +1,15 @@ #include <string.h>
-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; }