Re: [gentoo-dev] Re: Move x86/amd64 CPU extensions USE flags to a new USE_EXPAND variable

[Konstantin Tokarev]

13.12.2010, 18:53, "Francesco R" <vivo75@×××××.com>:
> 2010/12/13 Ryan Hill <dirtyepic@g.o>
>> On Sun, 12 Dec 2010 09:01:13 -0400
>> "Sergio D. Rodríguez Inclan" <srinclan@×××××.com> wrote:
>>
>>>   El 12/12/2010 02:46 a.m., Ryan Hill escribió:
>>> > I think the fewer sources of magic USE flags the better.  Maybe we could
>>> > document how to figure out what instruction sets a processor supports in the
>>> > handbook instead.
>>
>>> A good manual would be greatly appreciated :)
>>
>> I wrote a guide a couple weeks ago that might be a good starting point.
>>
>> http://en.gentoo-wiki.com/wiki/Hardware_CFLAGS
>
> if I read correctly the article on the wiki it does circa what the script reported below does.
> would be possible to adopt something similar for automatic C*FLAGS selection if someone step in willing to take the pain to mantain it.
>
> #!/usr/bin/python
> # Copyright 2010 Gentoo Foundation
> # Distributed under the terms of the GNU General Public License v2
> # Author: Francesco Riosa
> # extrapolated from http://en.gentoo-wiki.com/wiki/Hardware_CFLAGS, errors are mine
>
> # kate: encoding utf-8; eol unix
> # kate: indent-width 4; mixedindent off; replace-tabs on;
> # kate: remove-trailing-space on; space-indent on
>
> # echo "int main() { return 0; }" | gcc -march=native -v -E - 2>&1 | grep march
> # echo "int main() { return 0; }" | gcc -march=core2 -v -Q -x c - 2>&1
>
> """
> example output:
> ./hw-cflags.py
> extrapolating flags for gcc-4.4.5
>   useful flags: -march=core2 -msse4.1 --param l1-cache-size=32 --param l1-cache-line-size=64 --param l2-cache-size=2048 -mtune=generic
>   redundant:    -mcx16 -msahf
>
> extrapolating flags for gcc-4.5.1
>   useful flags: -march=core2 -msse4.1 --param l1-cache-size=32 --param l1-cache-line-size=64 --param l2-cache-size=2048 -mtune=core2
>   redundant:    -mcx16 -msahf
> """
>
> import os
> import time
> import fnmatch
> from subprocess import Popen, PIPE
>
> GCC_PATH = '/usr/bin/'
> GCC_LIST = fnmatch.filter(os.listdir(GCC_PATH), 'gcc-[0-9].*')
> GCC_LIST.sort()
>
> def extract_flags(gcccmd, header):
>     # get output from gcc
>     buf = ''
>     devnul = open('/dev/null', 'w')
>     p = Popen(gcccmd, stdin=PIPE, stdout=devnul, stderr=PIPE)
>     p.stdin.write("""int main() { return 0; }""")
>     p.stdin.close()
>     while p.poll() is None:
>         t = p.stderr.read()
>         buf = "buf%s" % t
>         time.sleep(0.01)
>     p.stderr.close()
>     devnul.close()
>
>     # parse it
>     flags = []
>     add = False
>     for line in buf.split('\n'):
>         if line.startswith(header):
>             add = True
>             flags += line.strip().split(' ')
>             continue
>         if add:
>             if line.startswith(' '):
>                 flags += line.strip().split(' ')
>             else:
>                 break
>
>     # extract flags we are interested in
>     t = []
>     march = ''
>     mtune = '-mtune=generic'
>     for i in xrange(len(flags)):
>         if flags[i].startswith('-m'):
>             if flags[i].startswith('-mtune'):
>                 mtune = flags[i]
>             elif flags[i].startswith('-march'):
>                 march = flags[i]
>             else:
>                 t.append(flags[i])
>         elif flags[i] == '--param':
>             t.append("%s %s" % (flags[i], flags[i+1]))
>     flags = t
>
>     return march, mtune, flags
>
> for gcc in GCC_LIST:
>
>     print "extrapolating flags for %s" % gcc
>
>     gcccmd = [ GCC_PATH + gcc, '-march=native', '-v', '-E', '-', ]
>     header='COLLECT_GCC_OPTIONS'
>     march, mtune, flags_native = extract_flags(gcccmd, header)
>
>     gcccmd = [ GCC_PATH + gcc, march, '-v', '-Q', '-x', 'c', '-', ]
>     header='options enabled:'
>     t, t, flags_enabled = extract_flags(gcccmd, header)
>
>     redundant_flags = []
>     useful_flags = []
>
>     for x in flags_native:
>         if x in flags_enabled:
>             redundant_flags.append(x)
>         else:
>             useful_flags.append(x)
>
>     if gcc < "gcc-4.5.0":
>         mtune = '-mtune=generic'
>
>     print "  useful flags: %s %s %s " % (march, " ".join(useful_flags), mtune)
>     print "  redundant:    %s" % " ".join(redundant_flags)
>     print

Note that for some architectures (e.g, PowerPC) you need to add "-mcpu" case
(-mcpu has the same meaning as -march on x86)


-- 
Regards,
Konstantin