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. Signed-off-by: Daniel Jacobowitz <dan@xxxxxxxxxxxxxxxx> Index: linux/include/asm-mips/checksum.h =================================================================== --- linux.orig/include/asm-mips/checksum.h 2005-09-19 21:00:48.000000000 -0400 +++ linux/include/asm-mips/checksum.h 2005-09-19 21:52:11.000000000 -0400 @@ -149,7 +149,7 @@ static inline unsigned int csum_tcpudp_n " daddu %0, %4 \n" " dsll32 $1, %0, 0 \n" " daddu %0, $1 \n" - " dsrl32 %0, %0, 0 \n" + " dsra32 %0, %0, 0 \n" #endif " .set pop" : "=r" (sum) -- Daniel Jacobowitz CodeSourcery, LLC
