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[PATCH] Fix wrong checksum calculation on 64-bit MIPS

To: linux-mips@linux-mips.org
Subject: [PATCH] Fix wrong checksum calculation on 64-bit MIPS
From: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Date: Wed, 24 Jan 2007 15:43:34 +0900 (JST)
Cc: ralf@linux-mips.org, Al Viro <viro@zeniv.linux.org.uk>, "David S. Miller" <davem@davemloft.net>
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
The commit 8e3d8433d8c22ca6c42cba4a67d300c39aae7822 ([NET]: MIPS
checksum annotations and cleanups) broke 64-bit MIPS.

The problem is the commit replaces some unsigned long with __be32.  On
64bit MIPS, a __be32 (i.e. unsigned int) value is represented as a
sign-extented 32-bit value in a 64-bit argument register.  So the
address 192.168.0.1 (0xc0a80001) is passed as 0xffffffffc0a80001 to
csum_tcpudp_nofold() but the asm code in the function expects
0x00000000c0a80001, therefore it returns a wrong checksum.  Explicit
cast to unsigned long is needed to drop high 32bit.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
---
diff --git a/include/asm-mips/checksum.h b/include/asm-mips/checksum.h
index 24cdcc6..20a81e1 100644
--- a/include/asm-mips/checksum.h
+++ b/include/asm-mips/checksum.h
@@ -159,7 +159,8 @@ static inline __wsum csum_tcpudp_nofold(__be32 saddr,
 #endif
        "       .set    pop"
        : "=r" (sum)
-       : "0" (daddr), "r"(saddr),
+       : "0" ((__force unsigned long)daddr),
+         "r" ((__force unsigned long)saddr),
 #ifdef __MIPSEL__
          "r" ((proto + len) << 8),
 #else

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