On 7/30/2018 11:39 AM, Ævar Arnfjörð
Bjarmason wrote:
The reason we're in this hole is because we use this
sha1collisiondetection library to do SHA-1, and the reason we have
issues with it specifically (not OpenSSL et al) is because its only
method of detecting endianness is at compile time.
When using gcc (no xlc available for Linux on Power)
POWER6 (Big Endian by definition)
root@x068:[/data/httpd/gcc]gcc -dM -E - < /dev/null | grep -i end
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __BIG_ENDIAN__ 1
#define __FLOAT_WORD_ORDER__ __ORDER_BIG_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define _BIG_ENDIAN 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
SLES12 on POWER8
suse12test:~ # gcc -dM -E - < /dev/null | grep -i end
#define __ORDER_LITTLE_ENDIAN__ 1234
#define _LITTLE_ENDIAN 1
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __ORDER_PDP_ENDIAN__ 3412
#define __LITTLE_ENDIAN__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
So, for compile time tests, when gcc is the compiler it seems the
following defines are available
__BIG_ENDIAN__, _BIG_ENDIAN, __LITTLE__ENDIAN__,
_LITTLE_ENDIAN
or something based on the value of __BYTE_ORDER__
I'll see if I can find something similar for xlc, but will only be
able to test xlc on AIX.
This didn't use to be the case, it was changed in this commit:
https://github.com/cr-marcstevens/sha1collisiondetection/commit/d597672
Dan Shumow: Since the commit message doesn't say why, can you elaborate
a bit on why this was done, i.e. is determining this at runtime harmful
for performance? If not, perhaps it would be best to bring this back, at
least as an option.