Messages in this thread Patches in this message |  | | From | Arnd Bergmann <> | Subject | Re: [GIT PULL] asm-generic fixes | Date | Tue, 23 Jun 2009 21:56:45 +0200 |
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On Tuesday 23 June 2009, Linus Torvalds wrote: > You might need to make 'result', 'carry', and 'w' be 'unsigned int' too.
Yes, you're right.
> Now, it's possible (even likely) that even with a 64-bit word, we'll never > actually do large enough areas that 'result' would ever have very many > bits set in the 32+ bit region, and since we do end up folding to 16 bits > twice (once after the loop and once at the end), it probably gets things > right in most cases. But I doubt "probably" is strong enough. Somebody > should check.
I think it would overrun only if we have more than 65536 u32 words of 0xffffffff in a single IP packet, on a 64 bit machine. A more obvious reason to change it is that it relies on from32to16() actually behaving like a from47to16() function on 64-bit. Changing it to use unsigned int throughout makes it both more obvious and more consistent between 32 and 64 bit unsigned long types.
> Or just see arch/alpha/lib/checksum.c, which does the whole 64-bit case. > Maybe lib/checksum.c should be lib/checksum_{32,64}.c.
Mike Frysinger earlier suggested just making the do_csum function optional in this file because this is the one that most architectures would override.
The alpha code is the only 64-bit platform implementing do_csum in C, so if Richard wants to use the generic code in its current form, he could simply override the do_csum implementation.
I've now added these two patches:
commit 217a8c7b6af924379a2083439b4bb606f332e7b1 Author: Arnd Bergmann <arnd@arndb.de> Date: Tue Jun 23 21:37:26 2009 +0200
lib/checksum.c: make do_csum optional Mike Frysinger suggested that do_csum should be optional so that an architecture can use the generic checksum code but still provide an optimized fast-path for the most critical function. This can mean an implementation using inline assembly, or in case of Alpha one using 64-bit arithmetic in C. Cc: Mike Frysinger <vapier@gentoo.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/lib/checksum.c b/lib/checksum.c index 886b48d..b08c2d0 100644 --- a/lib/checksum.c +++ b/lib/checksum.c @@ -37,6 +37,7 @@ #include <asm/byteorder.h> +#ifndef do_csum static inline unsigned short from32to16(unsigned int x) { /* add up 16-bit and 16-bit for 16+c bit */ @@ -102,6 +103,7 @@ static unsigned int do_csum(const unsigned char *buff, int len) out: return result; } +#endif /* * This is a version of ip_compute_csum() optimized for IP headers, commit 5cb59758c3e2170b24e9c0d659eb6c03872155c0 Author: Arnd Bergmann <arnd@arndb.de> Date: Tue Jun 23 21:22:58 2009 +0200
lib/checksum.c: use 32-bit arithmetic consistently
The use of 'unsigned long' variables in the 32-bit part of do_csum() is confusing at best, and potentially broken for long input on 64-bit machines.
This changes the code to use 'unsigned int' instead, which makes the code behave in the same (correct) way on both 32 and 64 bit machines.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/lib/checksum.c b/lib/checksum.c index b2e2fd4..886b48d 100644 --- a/lib/checksum.c +++ b/lib/checksum.c @@ -37,7 +37,7 @@ #include <asm/byteorder.h> -static inline unsigned short from32to16(unsigned long x) +static inline unsigned short from32to16(unsigned int x) { /* add up 16-bit and 16-bit for 16+c bit */ x = (x & 0xffff) + (x >> 16); @@ -49,7 +49,7 @@ static inline unsigned short from32to16(unsigned long x) static unsigned int do_csum(const unsigned char *buff, int len) { int odd, count; - unsigned long result = 0; + unsigned int result = 0; if (len <= 0) goto out; @@ -73,9 +73,9 @@ static unsigned int do_csum(const unsigned char *buff, int len) } count >>= 1; /* nr of 32-bit words.. */ if (count) { - unsigned long carry = 0; + unsigned int carry = 0; do { - unsigned long w = *(unsigned int *) buff; + unsigned int w = *(unsigned int *) buff; count--; buff += 4; result += carry;
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