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Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform

From "Jason A. Donenfeld" <Jason@zx2c4.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform
Date 2016-12-14 20:40 +0100
Message-ID <sOnzc-2MP-29@gated-at.bofh.it> (permalink)
References (1 earlier) <sO93b-1Im-11@gated-at.bofh.it> <sOhk5-6yG-21@gated-at.bofh.it> <sOm0p-1bT-5@gated-at.bofh.it> <sOma6-1ze-15@gated-at.bofh.it> <sOnpv-2DO-17@gated-at.bofh.it>
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Hi Hannes,

On Wed, Dec 14, 2016 at 8:22 PM, Hannes Frederic Sowa
<hannes@stressinduktion.org> wrote:
> I don't think this helps. Did you test it? I don't see reason why
> padding could be left out between `d' and `end' because of the flexible
> array member?

Because the type u8 doesn't require any alignment requirements, it can
nestle right up there cozy with the u16:

zx2c4@thinkpad ~ $ cat a.c
#include <stdint.h>
#include <stdio.h>
#include <stddef.h>
int main()
{
       struct {
               uint64_t a;
               uint32_t b;
               uint32_t c;
               uint16_t d;
               char x[];
       } a;
       printf("%zu\n", sizeof(a));
       printf("%zu\n", offsetof(typeof(a), x));
       return 0;
}
zx2c4@thinkpad ~ $ gcc a.c
zx2c4@thinkpad ~ $ ./a.out
24
18

Jason

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Thread

[PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-14 05:10 +0100
  Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-14 14:00 +0100
    Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-14 14:20 +0100
      Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-14 14:50 +0100
        RE: [PATCH v2 3/4] secure_seq: use siphash24 instead of  md5_transform David Laight <David.Laight@ACULAB.COM> - 2016-12-14 15:50 +0100
          Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-14 19:00 +0100
    Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of  md5_transform David Miller <davem@davemloft.net> - 2016-12-14 19:00 +0100
      Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-14 19:10 +0100
        Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-14 20:30 +0100
          Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-14 20:40 +0100
            Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-14 21:30 +0100
    Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform Tom Herbert <tom@herbertland.com> - 2016-12-14 21:20 +0100
      Re: [PATCH v2 3/4] secure_seq: use siphash24 instead of md5_transform "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-14 22:10 +0100

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