Re: PATCH: Add ifunc attribute

[Richard Guenther <richard dot guenther at gmail dot com>]

On Wed, Jun 24, 2009 at 5:19 PM, H.J. Lu<hjl.tools@gmail.com> wrote:
> On Wed, Jun 24, 2009 at 8:09 AM, Richard
> Guenther<richard.guenther@gmail.com> wrote:
>> On Wed, Jun 24, 2009 at 4:54 PM, Richard Henderson<rth@twiddle.net> wrote:
>>> On 06/24/2009 03:22 AM, Paolo Bonzini wrote:
>>>>
>>>> Looks a bit too like DWIM and too little like a specification. I think I
>>>> prefer option 1, in some cases you may want to call the trampoline and
>>>> having it accessible can help. With
>>>>
>>>> __typeof (foo) *
>>>> __attribute__ ((ifunc ("foo")))
>>>> foo_ifunc (void)
>>>> {
>>>> <return address of foo_{1,2,3}>
>>>> }
>>>>
>>>> you could call foo_ifunc if you wish in principle, and the header file
>>>> only has the prototype of foo as expected.
>>>
>>> I think I have to agree with you, Paolo. ?This example is the sort of
>>> thing I'd expect to actually be writing.
>>
>> You wouldn't call foo_ifunc but maybe one of foo_{1,2,3} directly. ?At
>> least for non-trivial foo_ifunc implementations.
>>
>> I still fail to see why we need the ifunc argument here though.
>>
>> __typeof (foo) *
>> __attribute__((ifunc))
>> foo_ifunc (void) asm("foo")
>> {
>> ?<return address of foo_{1,2,3}>
>> }
>>
>> works for me. ?Adding __attribute__((alias("foo_ifunc"))) should
>> make an alias available that you could call directly if you really
>> want to.
>>
>
> Is asm("foo") required for ifunc function?

No.  You can as well, if you don't have a conflicting declaration,
just write

void *
__attribute__((ifunc))
foo (void)
{
  <return address of foo_{1,2,3}>
}

the asm() was just to allow the header to be visible.

Richard.