From d02d6be5d52a98be32c93d2ea7a0068991774a20 Mon Sep 17 00:00:00 2001 From: Paul Mundt Date: Mon, 2 Jun 2008 12:40:14 +0900 Subject: [PATCH] sh: fix miscompilation of ip_fast_csum with gcc >= 4.3 As noted by Matthew Wilcox: Kyle McMartin just tracked down a bug on parisc to a missing "memory" clobber in the inline assembly implementation of ip_fast_csum. The FRV, SH and Xtensa ports are also missing a memory clobber, so I thought it would be polite to let you know. The bug manifests as dropped network packets (obviously they have the wrong checksum). It started appearing for parisc with GCC 4.3. The GCC manual says: If your assembler instructions access memory in an unpredictable fashion, add `memory' to the list of clobbered registers. This will cause GCC to not keep memory values cached in registers across the assembler instruction and not optimize stores or loads to that memory. I see that FRV has a 400 byte memory output which may prevent this problem from appearing, but SH and Xtensa have nothing to prevent this bug. Hope this saves you a few days of debugging. Signed-off-by: Paul Mundt --- include/asm-sh/checksum_32.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/asm-sh/checksum_32.h b/include/asm-sh/checksum_32.h index 4bc8357e889..14b7ac2f0a0 100644 --- a/include/asm-sh/checksum_32.h +++ b/include/asm-sh/checksum_32.h @@ -109,7 +109,7 @@ static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl) will assume they contain their original values. */ : "=r" (sum), "=r" (iph), "=r" (ihl), "=&r" (__dummy0), "=&z" (__dummy1) : "1" (iph), "2" (ihl) - : "t"); + : "t", "memory"); return csum_fold(sum); } -- 2.20.1