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Message-ID: <20150817160146.GA596@openwall.com>
Date: Mon, 17 Aug 2015 19:01:46 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: FMT_OMP_BAD
Kai, magnum -
On Mon, Aug 17, 2015 at 11:46:04PM +0800, Kai Zhao wrote:
> I find some formats set FMT_OMP flag without judging the value of
> _OPENMP. Such as mysql_fmt_plug.c:
>
> struct fmt_main fmt_MYSQL_fast =
> {
> {
> [...]
> MAX_KEYS_PER_CRYPT,
> FMT_CASE | FMT_8_BIT | FMT_SPLIT_UNIFIES_CASE | FMT_OMP,
> { NULL },
> tests
> },
> [...]
> }
That's correct. Please see formats.h:
#ifdef _OPENMP
/* Parallelized with OpenMP */
#define FMT_OMP 0x01000000
/* Poor OpenMP scalability */
#define FMT_OMP_BAD 0x02000000
#else
#define FMT_OMP 0
#define FMT_OMP_BAD 0
#endif
> I think it should be:
>
> struct fmt_main fmt_MYSQL_fast =
> {
> {
> [...]
> MAX_KEYS_PER_CRYPT,
> #ifdef _OPENMP
> FMT_OMP |
> #endif
> FMT_CASE | FMT_8_BIT | FMT_SPLIT_UNIFIES_CASE,
> { NULL },
> tests
> },
> [...]
> }
No, that's redundant. Some formats do it, but they should actually be
changed to use the simpler approach ...
... Unless this becomes wrong when we introduce FAST_FORMATS_OMP checks.
For example, rawMD5_fmt_plug.c has:
#include "formats.h"
#if !FAST_FORMATS_OMP
#undef _OPENMP
#endif
[...]
#ifdef _OPENMP
FMT_OMP | FMT_OMP_BAD |
#endif
and this combination makes sense to me. Listing FMT_OMP | FMT_OMP_BAD
unconditionally is no longer right, because this file may have _OPENMP
undefined even if formats.h had it defined.
Another approach could be to place the #undef before the very first
#include that might result in formats.h getting included. However, this
might be subtly wrong because formats.h includes params.h, in which we
also have unrelated _OPENMP checks that are better processed in the same
way for the entire program. I think this simpler approach would work
fine for now (the only _OPENMP check currently in params.h does not
affect format specifics), but it might not if we introduce even more
_OPENMP checks in header files later.
Yet we could give this simpler approach a try: move the #undef to be
before the very first #include in a format source file, and then list
FMT_OMP | FMT_OMP_BAD unconditionally.
I'll leave this decision to magnum.
Alexander
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