Re: [PATCH,TRIVIAL] Fix csum_ipv6_magic asm memory clobber

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 1 Oct 2009 01:01:38 +0200
Samuel Thibault <samuel.thibault@ens-lyon.org> wrote:

> Actually it hit Hurd's pfinetv4 when we tried to compile it with
> gcc-4.3 (bogus checksums).

That's important information!  I updated the changelog and added the
Cc:stable, thanks.


Full patch for netdev benefit:


From: Samuel Thibault <samuel.thibault@ens-lyon.org>

Just like ip_fast_csum, the assembly snippet in csum_ipv6_magic needs a
memory clobber, as it is only passed the address of the buffer, not a
memory reference to the buffer itself.

This caused failures in Hurd's pfinetv4 when we tried to compile it with
gcc-4.3 (bogus checksums).

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/x86/include/asm/checksum_32.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff -puN arch/x86/include/asm/checksum_32.h~x86-fix-csum_ipv6_magic-asm-memory-clobber arch/x86/include/asm/checksum_32.h
--- a/arch/x86/include/asm/checksum_32.h~x86-fix-csum_ipv6_magic-asm-memory-clobber
+++ a/arch/x86/include/asm/checksum_32.h
@@ -161,7 +161,8 @@ static inline __sum16 csum_ipv6_magic(co
 	    "adcl $0, %0	;\n"
 	    : "=&r" (sum)
 	    : "r" (saddr), "r" (daddr),
-	      "r" (htonl(len)), "r" (htonl(proto)), "0" (sum));
+	      "r" (htonl(len)), "r" (htonl(proto)), "0" (sum)
+	    : "memory");
 
 	return csum_fold(sum);
 }
_