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From: Martin Uecker <ma.uecker@gmail.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: Martin Uecker via Libffi-discuss <libffi-discuss@sourceware.org>,
	 Anthony Green <green@moxielogic.com>
Subject: Re: wide function pointer type
Date: Tue, 19 Oct 2021 14:13:12 +0200	[thread overview]
Message-ID: <a037654009f49c7ede0e7357ac2fa0ec080f8da5.camel@gmail.com> (raw)
In-Reply-To: <87o87lfhi3.fsf@oldenburg.str.redhat.com>

Am Dienstag, den 19.10.2021, 12:15 +0200 schrieb Florian Weimer:
> * Martin Uecker:
> 
> > > For GCC's nested function extension, there are no ABI concerns
> > > because the nested function definition and the thunk generation are
> > > always built from the same translation unit.  So GCC can just pick a
> > > custom calling convention, similar to what it does for other local,
> > > non-escaping functions.
> > 
> > Yes, but there are many other languages that make use of the
> > static chain.  So it would be good to have a standardized ABI
> > for this.
> 
> What's the exact use case for this?  These other languages do not
> usually have stable ABIs that inter-operate across different
> implementations.

One (of several) use cases is for language interoperability.

A common problem is to pass a function of a high-level
language as a callback to an C API.  This now often
requires special boiler plate code for each case and
there is no automatic way to do this. The fundamental
problem is that the C type can not express that a data
pointer belongs to a function pointer.

void foo(
  void (cb1)(void* data, int a), void* data1,
  void* other_data);  

Here a human (and maybe also a machine) could guess
that data1 belongs to cb1 but not other_data.  But
it is not clear and in more complicated cases
even less so.

void foo(void (_Wide cb1)(int a), void* other_data);


With the new type that would be unambiguous (and 
wrappers could then often be created automatically).
At least for the C API one would also expect ABI
stability.


Martin



  reply	other threads:[~2021-10-19 12:13 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-10 11:32 Martin Uecker
2021-10-17 23:35 ` Anthony Green
2021-10-18  5:33   ` Martin Uecker
2021-10-18  5:58     ` Martin Uecker
2021-10-18  7:36       ` Florian Weimer
2021-10-18  7:56         ` Martin Uecker
2021-10-19  9:22           ` Florian Weimer
2021-10-19  9:43             ` Martin Uecker
2021-10-19 10:15               ` Florian Weimer
2021-10-19 12:13                 ` Martin Uecker [this message]
2021-10-20  8:24                   ` Kaz Kylheku (libffi)
2021-10-20 18:52                     ` Martin Uecker
2021-10-20  9:10                   ` Florian Weimer
2021-10-20  9:21                     ` Martin Uecker
2021-10-20  9:27                       ` Florian Weimer
2021-10-20 17:27                     ` Kaz Kylheku (libffi)
2021-10-21  9:48                       ` Florian Weimer
2021-10-10 17:01 Kaz Kylheku (libffi)
2021-10-10 17:44 ` Martin Uecker
2021-10-10 17:49   ` Daniel Colascione
2021-10-10 18:05     ` Martin Uecker
2021-10-10 18:17       ` Daniel Colascione
2021-10-10 18:47         ` Martin Uecker
2021-10-10 18:57           ` Daniel Colascione
2021-10-10 19:24             ` Martin Uecker
2021-10-16  8:08               ` Jarkko Hietaniemi
2021-10-16  9:35                 ` Jarkko Hietaniemi
2021-10-10 18:31   ` Kaz Kylheku (libffi)

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