[PATCH] Initial support for __sptr and __uptr

[Aaron Ballman]

On Tue, May 14, 2013 at 8:50 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Tue, May 14, 2013 at 5:47 PM, Aaron Ballman <aaron at aaronballman.com>
> wrote:
>>
>> On Tue, May 14, 2013 at 8:42 PM, Richard Smith <richard at metafoo.co.uk>
>> wrote:
>> > On Tue, May 14, 2013 at 5:41 PM, Aaron Ballman <aaron at aaronballman.com>
>> > wrote:
>> >>
>> >> On Tue, May 14, 2013 at 8:34 PM, Richard Smith <richard at metafoo.co.uk>
>> >> wrote:
>> >> > On Tue, May 14, 2013 at 4:07 PM, Charles Davis <cdavis5x at gmail.com>
>> >> > wrote:
>> >> >>
>> >> >>
>> >> >> On May 14, 2013, at 4:26 PM, Aaron Ballman wrote:
>> >> >> >
>> >> >> >> Do __sptr and __uptr get different manglings?
>> >> >> >
>> >> >> > They do:
>> >> >> >
>> >> >> > void func( int * __ptr32 p ) {}
>> >> >> > void func2( int * __ptr64 p ) {}
>> >> >> >
>> >> >> > PUBLIC ?func@@YAXPAH at Z ; func
>> >> >> > PUBLIC ?func2@@YAXPEAH at Z ; func2
>> >> >> >
>> >> >> > Namely, the presence of E (rnk pointed this out previously).
>> >> >> He was asking about __sptr and __uptr :). They don't by the way:
>> >> >>
>> >> >> > cl /c test.cpp
>> >> >> [extraneous banner output omitted]
>> >> >> > dumpbin /symbols test.obj
>> >> >> [...]
>> >> >> 00F 00000010 SECT4  notype ()    External     | ?func@@YAXPAH at Z
>> >> >> (void
>> >> >> __cdecl func(int *))
>> >> >> 010 00000020 SECT4  notype ()    External     | ?func2@@YAXPAH at Z
>> >> >> (void
>> >> >> __cdecl func2(int *))
>> >> >
>> >> >
>> >> > Thanks. One more thing:
>> >> >
>> >> > template<typename T> void f(void **p, T *q) { *p = *q; }
>> >> >
>> >> > void *g(int *__ptr32 __sptr a) {
>> >> >   void *result;
>> >> >   f(&result, &a);
>> >> >   return result;
>> >> > }
>> >> > void *h(char *__ptr32 __uptr a) {
>> >> >   void *result;
>> >> >   f(&result, &a);
>> >> >   return result;
>> >> > }
>> >> >
>> >> > int main() {
>> >> >   printf("%p\n", g((int *__ptr32 __sptr)0xdeadbeef));
>> >> >   printf("%p\n", h((char *__ptr32 __uptr)0xdeadbeef));
>> >> > }
>> >> >
>> >> > Does one of these get sign-extended and the other one get
>> >> > zero-extended?
>> >>
>> >> The first is sign extended, and the second is zero extended in 64-bit.
>> >
>> >
>> > What happens if you change the two 'char's to 'int's?
>>
>> Both sign extend.  Is that due to the template instantiation?
>
>
> Yeah, both are instantiated with canonically-equivalent arguments. That is
> madness, and we shouldn't support it unless we have a strong compatibility
> argument to do so.

I don't imagine that to be a problem.

> Can we get away with rejecting __uptr and ignoring
> __sptr?

In such an example, or on the whole?  I don't think we can do it on
the whole because the purpose for this feature is to aid with WOW64
development and interop, and __uptr is really the only one of interest
(__sptr is the default behavior for conversion).

~Aaron