Re: [PATCH] Add flags for powerpc in order to avoid exceptions

[Vladimir 'φ-coder/phcoder' Serbinenko]

On 09.10.2014 02:38, Paulo Flabiano Smorigo wrote:
> Mon, Sep 29, 2014 at 10:30:16PM +0400, Andrei Borzenkov wrote:
>> В Sat, 27 Sep 2014 09:06:53 +0400
>> Andrei Borzenkov <address@hidden> пишет:
>>
>>> В Fri, 26 Sep 2014 16:29:40 -0300
>>> Paulo Flabiano Smorigo <address@hidden> пишет:
>>>
>>>> * conf/Makefile.common [COND_powerpc_ieee1275] (CFLAGS_PLATFORM): Add
>>>> -msoft-float -mno-vsx -mno-altivec.
>>>>
>>>> Also-By: Adhemerval Zanella <address@hidden>
>>>> ---
>>>>  ChangeLog            | 7 +++++++
>>>>  conf/Makefile.common | 3 +++
>>>>  2 files changed, 10 insertions(+)
>>>>
>>>> diff --git a/ChangeLog b/ChangeLog
>>>> index 192e8bc..40eb90c 100644
>>>> --- a/ChangeLog
>>>> +++ b/ChangeLog
>>>> @@ -1,3 +1,10 @@
>>>> +2014-09-26  Paulo Flabiano Smorigo  <address@hidden>
>>>> +
>>>> +  Add flags for powerpc in order to avoid exceptions
>>>> +
>>>> +  * conf/Makefile.common [COND_powerpc_ieee1275] (CFLAGS_PLATFORM): Add
>>>> +  -msoft-float -mno-vsx -mno-altivec.
>>>> +
>>>>  2014-09-25  Colin Watson  <address@hidden>
>>>>  
>>>>    Fix in-tree --platform=none
>>>> diff --git a/conf/Makefile.common b/conf/Makefile.common
>>>> index 51fbaf9..57c491a 100644
>>>> --- a/conf/Makefile.common
>>>> +++ b/conf/Makefile.common
>>>> @@ -22,6 +22,9 @@ endif
>>>>  if COND_arm64
>>>>    CFLAGS_PLATFORM += -mcmodel=large
>>>>  endif
>>>> +if COND_powerpc_ieee1275
>>>> +  CFLAGS_PLATFORM += -msoft-float -mno-vsx -mno-altivec
>>>> +endif
>>>>  
>>>>  #FIXME: discover and check XEN headers
>>>>  CPPFLAGS_XEN = -I/usr/include
>>>
>>> Thank you! I confirm that this patch works and does not break grub on
>>> earlier CPU :)
>>>
>>> There are still differences in generated code, so we probably need to
>>> tune some more flags.
>>
>> I looked at compiler options for PowerPC and I think instead of trying
>> to catch individual flags which may change with every release we should
>> simply force the most common platform by
>>
>> +if COND_powerpc_ieee1275
>> +  CFLAGS_PLATFORM += -mcpu=powerpc -mtune=powerpc
>> +endif
>>
>>
>> This makes sure result is identical on every platform and provides most
>> generic code that is expected to run on every(?) system.
>>
>> WDYT?
> 
> Hi Andrei,
> 
> Sorry to take so long to answer your question.
> 
> After an internal discussion with some toolchain experts we found out
> that your approach is good. It works and it's more generic but we think
> that we should change it a little bit:
> 
>  * skip -mtune, not really necessary
>  * add "-msoft-float" to be completly safe.
> 
> Something like:
> 
> +if COND_powerpc_ieee1275
> +  CFLAGS_PLATFORM += -mcpu=powerpc -msoft-float
> +endif
> 
> This approach is similar to what the linux kernel do.
Can you add -msoft-float to all archs? Other than that proposition looks
good

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