From: Tom Tromey <tom@tromey.com>
To: "Kaz Kylheku \(libffi\)" <382-725-6798@kylheku.com>
Cc: libffi-discuss@sourceware.org
Subject: Re: Cosure return value issue on Linux PPC64
Date: Mon, 29 May 2017 12:31:00 -0000 [thread overview]
Message-ID: <8737bnetf4.fsf@bapiya> (raw)
In-Reply-To: <53985e874a349c551e7943677d21c766@mail.kylheku.com> (Kaz Kylheku's message of "Sat, 27 May 2017 09:59:36 -0700")
Kaz> Is this documented somewhere?
A while back I tried to document all these little oddities in the
manual. It's difficult and ABI-breaking to fix libffi to be more in
line with user expectation, but at least in the meantime the docs can be
correct...
The closure docs say:
@item ret
[...]
Otherwise, @var{fun} must fill the object to which this points,
following the same special promotion behavior as @code{ffi_call}.
That is, in most cases, @var{ret} points to an object of exactly the
size of the type specified when @var{cif} was constructed. However,
integral types narrower than the system register size are widened. In
these cases your program may assume that @var{ret} points to an
@code{ffi_arg} object.
I hope this helps, but if it's still insufficiently clear, I'd
appreciate suggestions for how to improve it.
From your other note:
Kaz> I'm not a complete idiot; I was taken for a ride by the simple
Kaz> example from some (perhaps outdated?) libffi texinfo
Kaz> documentation. This one:
You're definitely not an idiot, this has bitten many people, has been
asked on StackOverflow, has been filed as a bug in github a few times,
etc.
Alan Modra fixed up this documentation example back in 2013, according
to git blame. Seems like libffi is overdue for a release :-)
Anyway, I think the in-tree docs should be a bit clearer here. For
example they mention the promotion behavior now.
Tom
next prev parent reply other threads:[~2017-05-29 12:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-27 16:59 Kaz Kylheku (libffi)
2017-05-29 7:44 ` Andrew Haley
2017-05-29 12:31 ` Tom Tromey [this message]
2017-05-29 15:30 ` Andrew Haley
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