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Re: [PATCH] Add variadic support


On 2011/2/24 12:20 AM, David Gilbert wrote:
> On 23 February 2011 13:25, Chung-Lin Tang <cltang@linaro.org> wrote:
>> On 2011/2/23 09:11 PM, David Gilbert wrote:
>>> In ARM's ffi_prep_cif_machdep I have:
>>>
>>> +#ifdef __ARM_PCS_VFP
>>> +  /* VFP uses the standard ABI for variadic functions */
>>> +  if ((cif->abi == FFI_VFP) && (cif->nfixedargs != 0))
>>> +    cif->abi = FFI_SYSV;
>>> +#endif
>>>
>>> and that's the only active change that's needed.
>>
>> I suggest removing the #ifdef __ARM_PCS_VFP #ifdef.  We always have
>> support for both FFI_SYSV and FFI_VFP compiled in, so it doesn't make
>> sense to leave this bit of logic out when we are under __ARM_PCS.
> 
> I could do, although cif->nfixedargs is also not present except in the
> VFP case, so
> it would still need an ifdef.
> 
> I did that since I thought it best not to change the layout of the CIF
> structure for
> existing ARM builds.

Sigh...you're right about the layout issue :(

Still I think it's best we keep the full FFI_SYSV/VFP capabilities in,
or we'll have the weird case of "FFI_VFP with buggy variadics" under softfp.

I suggest moving the nfixedargs field into the ARM FFI_EXTRA_CIF_FIELDS,
placed after the current VFP fields; this means doing away with the
FFI_TARGET_SPECIFIC_VARIADIC symbol, and probably having a
machine-specific ffi_prep_cif_var_machdep() function, analogous to the
current ffi_prep_cif_machdep().

ffi_prep_cif_var_machdep() can then save things like 'number of fixed
arguments' from the ffi_prep_cif_var() arguments if it is necessary for
that architecture.

Chung-Lin


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