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.
