I have just replied to
https://github.com/cr-marcstevens/sha1collisiondetection/pull/42
I checked a gcc compiler on AIX, and I have the defines for vac.
I do not have access yet to SLES or RHEL (or Ubuntu), just a "free
Debian" on my Power6.
* my conclusions|recommendations:
a) AIX is always Big Endian, the define _AIX can be used to determine if AIX
b) POWER7 and earlier are always Big Endian
c) assuming lscpu is always available on Linux systems a command (in
configure?) could be used:
root@x074:/usr/bin# lscpu | grep -i endian
Byte Order: Big Endian
d) some linux systems (in any case latest versions of RHEL and SLES
enterprise) should have a file named lparcfg in /proc
(/proc/{powerppc|ppc64|ppc64le|ppc64el}/lparcfg - and it might be in
that file. Need to get onto a (POWER8|POWER9) system to check.
Hope this helps:
details re: define of _AIX
root@x068:[/data/httpd/gcc]gcc -dM -E - < /dev/null | grep AIX | head -1
#define _AIX 1
michael@x071:[/home/michael]/usr/bin/grep -p DEFLT:
/etc/vac.cfg.[567][123] | grep options\
options =
-D_AIX,-D_AIX32,-D_AIX41,-D_AIX43,-D_AIX50,-D_AIX51,-D_AIX52,-D_AIX53,-D_IBMR2,-D_POWER
options =
-D_AIX,-D_AIX32,-D_AIX41,-D_AIX43,-D_AIX50,-D_AIX51,-D_AIX52,-D_AIX53,-D_AIX61,-D_IBMR2,-D_POWER
options =
-D_AIX,-D_AIX32,-D_AIX41,-D_AIX43,-D_AIX50,-D_AIX51,-D_AIX52,-D_AIX53,-D_AIX61,-D_AIX71,-D_IBMR2,-D_POWER
options =
-D_AIX,-D_AIX32,-D_AIX41,-D_AIX43,-D_AIX50,-D_AIX51,-D_AIX52,-D_AIX53,-D_AIX61,-D_AIX71,-D_AIX72,-D_IBMR2,-D_POWER
michael@x071:[/home/michael]ls /etc/vac.cfg.[567][123]
/etc/vac.cfg.53 /etc/vac.cfg.61 /etc/vac.cfg.71 /etc/vac.cfg.72
On 7/30/2018 8:39 PM, Daniel Shumow wrote:
The change was definitely made for performance. Removing the if
statements, conditioned upon endianess was an approx 10% improvement,
which was very important to getting this library accepted into git.
Thanks,
Dan
On Mon, Jul 30, 2018 at 11:32 AM, Junio C Hamano <gits...@pobox.com
<mailto:gits...@pobox.com>> wrote:
Junio C Hamano <gits...@pobox.com <mailto:gits...@pobox.com>> writes:
> Ævar Arnfjörð Bjarmason <ava...@gmail.com
<mailto:ava...@gmail.com>> writes:
>
>> And, as an aside, the reason we can't easily make it better
ourselves is
>> because the build process for git.git doesn't have a facility
to run
>> code to detect this type of stuff (the configure script is always
>> optional). So we can't just run this test ourselves.
>
> It won't help those who cross-compile anyway. I thought we declared
> "we make a reasonable effort to guess the target endianness from the
> system header by inspecting usual macros, but will not aim to cover
> every system on the planet---instead there is a knob to tweak it for
> those on exotic platforms" last time we discussed this?
Well, having said all that, I do not think I personally mind if
./configure learned to include a "compile small program and run it
to determine byte order on the build machine" as part of "we make a
reasonable effort" as long as it cleanly excludes cross building
case (and the result is made overridable just in case we misdetect
the "cross-ness" of the build).
