Calling convention for "Routines for floating point emulation"

[Joseph Myers]

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 
use the VFP ABI when compiling for that ABI.

-- 
Joseph S. Myers
joseph@codesourcery.com