[U-Boot] [RFC][PATCH] ARMV7: Patch to fix hard float build issues

[Måns Rullgård]

Albert ARIBAUD <albert.aribaud at free.fr> writes:

> Le 19/02/2011 15:06, Alexander Holler a écrit :
>> Am 19.02.2011 14:51, schrieb Albert ARIBAUD:
>>> Le 19/02/2011 14:25, Måns Rullgård a écrit :
>>>
>>>>> So whats the reasoning to use -msoft-float as it is currently done? To
>>>>> confuse people? ;)
>>>>
>>>> I guess it's there to make sure no floating-point instructions make it
>>>> into u-boot, even though floats are not used in the code. Perhaps
>>>> someone was paranoid.
>>>
>>> I think also that there is no choice but to have a float option for ARM
>>> C, either 'soft' or 'hard' (or 'softfp', actually, which is 'hard' with
>>> the 'soft' calling conventions), because the C compiler does not allow
>>> 'no floats', and anyway the C language *requires* to have some sort of
>>> float support.
>>
>> As it is on every platform.
>
> Indeed.
>
>>> Actually if you don't specify any float option, the C toolchain will
>>> choose one, which is just the same in the end: *some* float option is
>>> chosen.
>>
>> Every compiler has dozens of options which are set to a default value.
>
> Granted. But not all of them relate to hardware which may or may not be 
> available.
>
>>> And since some option must be chosen, I prefer that U-Boot make the
>>> explicit decision, and choose soft float for the reasons I already
>>> exposed.
>>
>> I don't see any reason to explicitly set an option for something which
>> isn't used, but I know of many reasons to avoid such. ;)
>
> At least there is one reason for having -msoft-float even though no 
> floating point should be used in U-Boot : it helps catching cases where 
> some code in U-Boot tries to use hard float. :)

There is one further complication here.  If the compiler was built with
-mfpu=neon as default, it might emit neon instructions for pure integer
code.  For the purpose of this discussion, such instructions should
still be regarded as floating-point since they are tied to the VFP.
Such code generation is disabled by -msoft-float.

-- 
Måns Rullgård
mans at mansr.com