Messages in this thread Patch in this message | | | From | Arnd Bergmann <> | Subject | Re: [PATCH 05/17] Blackfin: convert to generic checksum code | Date | Fri, 19 Jun 2009 11:05:37 +0200 |
| |
On Friday 19 June 2009, Mike Frysinger wrote: > On Mon, Jun 15, 2009 at 07:04, Arnd Bergmann wrote: > > On Sunday 14 June 2009, Mike Frysinger wrote: > >> The Blackfin port only implemented an optimized version of the > >> csum_tcpudp_nofold function, so convert everything else to the new > >> generic code. > >> > >> Signed-off-by: Mike Frysinger <vapier@gentoo.org> > > > > Have you tested this one well? I was as careful as possible with the > > version I added, but it was basically only tested on microblaze, which > > has a different endianess from blackfin. Some areas of the code may be > > sensitive to this. > > i did some tests and it looks like do_csum() is broken :(
Thanks for testing. Indeed it turns out to be an endian-problem with the handling of the last byte:
> here's the input: > do_csum({ 0xff 0xfb 0x01 }, 3) > > and here's the output: > Blackfin: 0xfc00 > generic: 0xfcff > > if i run the two funcs on my x86, i see similar behavior. the > attached csum-test.c contains the csum code from lib/checksum.c and > arch/blackfin/lib/checksum.c and shows the problem.
x86 and blackfin are both little-endian, so your variant is correct there. They add the 0x01 to the low byte of the 16-bit word, while on big-endian machines, you have to add it to the high byte.
> -mike > csum-test.c > #include <stdio.h> > > static inline unsigned short gen_from32to16(unsigned long x) > { > /* add up 16-bit and 16-bit for 16+c bit */ > x = (x & 0xffff) + (x >> 16); > /* add up carry.. */ > x = (x & 0xffff) + (x >> 16); > return x; > } > > static unsigned int gen_do_csum(const unsigned char *buff, int len) > { > ... > if (len & 1) > result += (*buff << 8);
On little-endian, this needs to be
if (len & 1) result += *buff;
> static unsigned short bf_do_csum(const unsigned char *buff, int len) > { > ... > if (len > 0) > sum += *buff;
Same problem, on big-endian this would need to be if (len > 0) sum += (*buff << 8);
The bug potentially also exists in arch/sh/lib64/c-checksum.c, which only works on little-endian machines, while the sh architecture code appears dual-endian. Paul, is your lib64/c-checksum.c implementation potentially run on big-endian machines, or is sh64 guaranteed to be little-endian?
I've committed the patch below now.
Arnd <><
--- From e01fed86629737809c46dcb8b807347e84640b70 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann <arnd@arndb.de> Date: Fri, 19 Jun 2009 10:41:19 +0200 Subject: [PATCH] lib/checksum.c: fix endianess bug
The new generic checksum code has a small dependency on endianess and worked only on big-endian systems. I could not find a nice efficient way to express this, so I added an #ifdef. Using 'result += le16_to_cpu(*buff);' would have worked as well, but would be slightly less efficient on big-endian systems and IMHO would not be clearer.
Also fix a bug that prevents this from working on 64-bit machines. If you have a 64-bit CPU and want to use the generic checksum code, you should probably do some more optimizations anyway, but at least the code should not break.
Reported-by: Mike Frysinger <vapier@gentoo.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- lib/checksum.c | 6 +++++- 1 files changed, 5 insertions(+), 1 deletions(-)
diff --git a/lib/checksum.c b/lib/checksum.c index 12e5a1c..4a1c84a 100644 --- a/lib/checksum.c +++ b/lib/checksum.c @@ -71,7 +71,7 @@ static unsigned int do_csum(const unsigned char *buff, int len) if (count) { unsigned long carry = 0; do { - unsigned long w = *(unsigned long *) buff; + unsigned long w = *(unsigned int *) buff; count--; buff += 4; result += carry; @@ -87,7 +87,11 @@ static unsigned int do_csum(const unsigned char *buff, int len) } } if (len & 1) +#ifdef __LITTLE_ENDIAN + result += *buff; +#else result += (*buff << 8); +#endif result = from32to16(result); if (odd) result = ((result >> 8) & 0xff) | ((result & 0xff) << 8); -- 1.6.3.1
| |