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Re: [PATCH] Fix TCP/UDP checksums on the Broadcom SB-1

To: Daniel Jacobowitz <>
Subject: Re: [PATCH] Fix TCP/UDP checksums on the Broadcom SB-1
From: Ralf Baechle <>
Date: Tue, 20 Sep 2005 12:01:02 +0100
In-reply-to: <>
Original-recipient: rfc822;
References: <>
User-agent: Mutt/
On Mon, Sep 19, 2005 at 11:28:18PM -0400, Daniel Jacobowitz wrote:

> The type of sum in csum_tcpudp_nofold is "unsigned int", so when we assign
> to it in an asm() block, and we're running on a system with 64-bit
> registers, it is vitally important that we sign extend it correctly before
> returning to C.  Otherwise the stray high bits will be preserved into
> csum_fold, and on the SB-1 processor, 32-bit arithmetic on a non
> sign-extended register will yield surprising results.
> This caused incorrect checksums in some UDP packets for NFS root.  The
> problem was mild when using a 10.0.1.x IP address, but severe when
> using 192.168.1.x.

Good catch.  And just to increase the func factor this bug did also apply
to 2.4.  Applied,


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