lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Tue, 13 Mar 2007 14:38:32 +0100
From:	Eric Dumazet <>
To:	Andi Kleen <>
Cc:	David Miller <>,,,
Subject: Re: bridge: faster compare for link local addresses

On Tuesday 13 March 2007 15:01, Andi Kleen wrote:
> David Miller <> writes:
> > From: Rick Jones <>
> > Date: Mon, 12 Mar 2007 17:05:39 -0700
> >
> > > Being paranoid - are there no worries about the alignment of dest?
> >
> > If it's an issue, it's an issue elsewhere too, as the places
> > where Stephen took this idiomatic code from is the code
> > ethernet handling and that runs on every input packet via
> > eth_type_trans().
> As a quick note -- when you tell gcc the expected alignment
> by using correct types then moderm gcc should generate fast inline code
> for memcpy/memcmp/etc. by itself. It only falls back to a slow generic
> function when it cannot figure out the alignment or the size.
> So I expect just using u32 * instead of char * should have the same
> effect and would be somewhat cleaner and the memcmp could be kept.

For memcpy() yes you can have some optimizations.

But memcmp() has a strong semantic (in libc). memcmp(a, b, 6) should do 6 byte 
compares and conditional branches, regardless of a/b alignment.
Or use the x86 "rep cmpsb" instruction that basically has the same cost.

The trick we use in compare_ether_addr() reduces to one some arithmetic and 
one test.

return ((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2])) != 0;

I found this line as clean as memcmp(a, b, 6)

(On x86_64, were alignment is not mandatory, we could do :

((*(long *)a ^ *(long*)b) << 16) != 0)

(only if we can always read two extra bytes without faulting, of course :) )

To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to
More majordomo info at

Powered by blists - more mailing lists