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Re: PATCH: Add ifunc attribute


On Fri, Jun 26, 2009 at 10:21 PM, H.J. Lu<hjl.tools@gmail.com> wrote:
> On Fri, Jun 26, 2009 at 12:13 PM, Roland McGrath<roland@redhat.com> wrote:
>>> > Why wouldn't Roland's proposal work with C++?
>>>
>>> I am not sure it will work for C++, especially for member functions.
>>
>> That isn't actually an answer to the question, you know.
>> Why wouldn't it?
>>
>> I had not thought about name mangling before, but I don't see a special
>> problem if you treat it in what seems to me the obvious way. ?With:
>>
>> __typeof (foo) *foo_finder (void) __attribute__ ((ifunc ("foo")));
>>
>> The mangling of "foo" goes with the type of "foo". ?Either you could say
>> that a foo prototype must be in scope, and it literally uses the type of
>> "foo", but that is probably a confusing definition given overloading.
>> With C++ overloading you can't actually use __typeof (foo), of course.
>>
>> void foo (int);
>> void foo (float);
>> void (*foo_int_finder (void)) (int) __attribute__ ((ifunc ("foo")));
>> void (*foo_float_finder (void)) (float) __attribute__ ((ifunc ("foo")));
>>
>> So what you say is that the function type to which *_finder's return type
>> is a pointer, is the type of "foo" for name-mangling purposes. ?Same with
>> s/foo/someclass::foo/ for a member function.
>>
>
> I have some C/C++ examples with valid and invalid cases:
>
> http://gcc.gnu.org/bugzilla/attachment.cgi?id=18076
>
> How will you get the same functionality with other
> options?

I use a proper asm("...") with a mangled name.  I don't see what should
be special with C++ about ifunc if you do not want to play games
with inheriting the attribute for overloads.

Richard.


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