Calling convention for "Routines for floating point emulation"

Yichao Yu yyc1992@gmail.com
Wed Sep 28 23:54:00 GMT 2016


On Wed, Sep 28, 2016 at 7:45 PM, Yichao Yu <yyc1992@gmail.com> wrote:
> On Wed, Sep 28, 2016 at 7:39 PM, Joseph Myers <joseph@codesourcery.com> wrote:
>> On Wed, 28 Sep 2016, Yichao Yu wrote:
>>
>>> In particular, it seems that on all the platforms with a
>>> arm*-*-gnueabihf triple I've checked (alarm armv7h, alarm armv6h,
>>> debian armhf, fedora armv7hl) the __powidf2 function (and possibly
>>> many others) are compiled with the AAPCS VFP calling convention, which
>>> is also how it is used by gcc. However, LLVM dev (CC'd) claims that
>>> these routines are meant to be always using soft floating point
>>> calling convention even on platforms using hard floating point ABI.
>>
>> The RTABI functions should use the base AAPCS calling conventions.  That
>> was something I dealt with when working on the implementation of the VFP
>> ABI variant <https://gcc.gnu.org/ml/gcc-patches/2009-05/msg00591.html>.
>>
>> Except where an external ABI defines things like that, the normal
>> expectation for libgcc functions is that they have the same ABI as for an
>> ordinary C function with the same prototype.  That is, since libgcc.texi
>> gives a prototype for __powidf2 without saying anything special about its
>> ABI, and since it is not a function defined in RTABI, it can be taken to
>
> I guess other ppl on the list probably know this but what's the list
> of function in RTABI?

Is it http://infocenter.arm.com/help/topic/com.arm.doc.ihi0043d/IHI0043D_rtabi.pdf
?

>
> Thanks.
>
>> use the VFP ABI when compiling for that ABI.
>>
>> --
>> Joseph S. Myers
>> joseph@codesourcery.com



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