Re: Floating-point variadic function call

[Richard Henderson <rth@redhat.com>]

On 10/10/2016 02:27 AM, Damien Thébault wrote:
> On Mon, Oct 10, 2016 at 12:17:03AM -0700, Andrew Pinski wrote:
>>> I tested on a x86_64 computer both 64-bit and 32-bit versions (the
>>> latter compiled with -m32) as well as ARM under qemu.
>>> In all those cases, I didn't get the proper result with floats while
>>> doubles are ok, as well as chars.
>>
>> That is because the variadic function ABI is different from the normal
>> argument ABI on ARM hard-float EABI.  Basically for variadic functions
>> float are passed via the integer registers while for normal functions,
>> they are passed via the vfp registers.
>>
>> Basically you need to use variadic function support in libff.  Use
>> ffi_prep_cif_var instead of ffi_prep_cif and then don't do:
>>
>>     for(i=1 ; i<10 ; i++)
>>     {
>>         arg_types[i] = &ffi_type_float;
>>     }
>
> I'm actually using ffi_prep_cif_var() for the variadic call, but what
> should I put as arg_type then ?

You must do the mandatory C promotion yourself.  Put ffi_type_double.


r~