linux-kernel - Re: [PATCH,TRIVIAL] Fix csum_ipv6

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Message-Id: <20090930161939.8c6d140a.akpm@linux-foundation.org>
Date:	Wed, 30 Sep 2009 16:19:39 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Samuel Thibault <samuel.thibault@...-lyon.org>
Cc:	hpa@...or.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	tglx@...utronix.de, davem@...emloft.net, andi@...stfloor.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH,TRIVIAL] Fix csum_ipv6_magic asm memory clobber

On Thu, 1 Oct 2009 01:01:38 +0200
Samuel Thibault <samuel.thibault@...-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@...-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@...-lyon.org>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: <stable@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-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);
 }
_

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