Re: problem with __init_cpu_features()

[The Source <thesourcehim@gmail.com>]

19.05.2016 16:07, The Source пишет:
> 19.05.2016 11:49, The Source пишет:
>> 19.05.2016 10:37, The Source пишет:
>>> 18.05.2016 21:53, Carlos O'Donell пишет:
>>>> On Wed, May 18, 2016 at 10:55 AM, Carlos O'Donell
>>>> <carlos@systemhalted.org> wrote:
>>>>> On Wed, May 18, 2016 at 10:37 AM, The Source 
>>>>> <thesourcehim@gmail.com> wrote:
>>>>>> Hello, I'm trying to run my application on Cyrix Cx486SLC based 
>>>>>> system. But
>>>>>> application (built for i486 as well as glibc) crashes on illegal 
>>>>>> instruction
>>>>>> inside __init_cpu_features(). As far as I understand this CPU 
>>>>>> does not
>>>>>> support cpuid (/proc/cpuinfo reports cpuid level -1 and 
>>>>>> /dev/cpu/0/cpuid can
>>>>>> not be read with i/o error), so that might be the problem. Is 
>>>>>> there a way to
>>>>>> avoid using __cpuid()? My glibc version is 2.22
>>>>> You must use specific CFLAGS or CC to indicate you are building for a
>>>>> pre-i586 target, that will disable unconditional cpuid usage, and
>>>>> enable the checks required to verify cpuid is usable.
>>>>>
>>>>> If you are cross-compiling from an x86_64 box I would recommend
>>>>> CC="gcc -m32 -march=i486" instead to ensure that regardless of flags
>>>>> you build for i486.
>>>>>
>>>>> Just to check I kicked off a build for i486 locally to see if runs
>>>>> into any problems.
>>>> i486 builds just fine and I verified it calls __get_cpuid_max to check
>>>> for cpuid feature.
>>>>
>>>> Test results look good too.
>>>>
>>>> Cheers,
>>>> Carlos.
>>>
>>> Unfortunately, adding those flags to compiler for both libc and 
>>> application did not help. I found out that __init_cpu_features is 
>>> located inside libpthread somehow. So my application crashes when it 
>>> uses threads. Could there be some unwanted optimization inside pthread?
>>>
>> Hmm, I see some strange things in glibc config.log. It appears that 
>> some subconfigs are called with i686 despite main script is called 
>> with --with-cpu=i486. Trying to figure out if it's configure bug or 
>> crosstools-ng.
>>
>>
> I'm out of ideas. I tried to restrict gcc from building anything but 
> i486 (by passing the following flags to configure of both gcc and 
> glibc: --with-cpu=i486 --with-cpu-32=i486 --with-arch=i486 
> --with-arch-32=i486 --enable-targets=i486), but it did not help, I 
> still see those i686 successful tests in config.log and libpthread 
> still has __init_cpu_features. If anyone have any idea how to forbid 
> i686, I'm open for suggestions, thank you.
>
>
Some more findings:

1. I changed libc code slightly to avoid using cpuid inside pthread:

sysdeps/unix/sysv/linux/x86/elision-conf.c

Replaced all usage of HAS_RTM to 0:

  __elision_available = 0;//HAS_RTM;
#ifdef ENABLE_LOCK_ELISION
   __pthread_force_elision = __libc_enable_secure ? 0 : __elision_available;
#endif
   //if (!HAS_RTM)
     __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks */

2. And crash has gone from libpthread. But poped up in different place:

libgcc_s: libgcc/config/i386/cpuinfo.c

__cpu_indicator_init function uses cpuid


So cpuid pops up here and there even if everything is built for i486. 
Isn't there a way to completely get rid of it?



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