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On 7/30/2018 11:39 AM, Ævar Arnfjörð
Bjarmason wrote:
When using gcc (no xlc available for Linux on Power)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. 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. |
