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Re: RFC: Support non-standard extension (call via casted function pointer)
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Michael Karcher <debian at mkarcher dot dialup dot fu-berlin dot de>,gcc at gcc dot gnu dot org
- Cc: John Paul Adrian Glaubitz <glaubitz at physik dot fu-berlin dot de>,Debian m68k <debian-68k at lists dot debian dot org>,Andreas Schwab <schwab at linux-m68k dot org>,doko at debian dot org
- Date: Tue, 26 Jan 2016 08:01:13 +0100
- Subject: Re: RFC: Support non-standard extension (call via casted function pointer)
- Authentication-results: sourceware.org; auth=none
- References: <56A697DE dot 5090207 at mkarcher dot dialup dot fu-berlin dot de>
On January 25, 2016 10:47:10 PM GMT+01:00, Michael Karcher <email@example.com> wrote:
>Hello gcc developers,
>as discussed in https://ghc.haskell.org/trac/ghc/ticket/11395 (and
>forwarded as PR c/69221), ghc generates non-compliant C code that is
>compiled as intended on m68k. This is because its internal Cmm (a C--
>dialect) to C compiler needs to declare external functions (no varargs)
>without fixing the type. It currently uses "unspecified-function-type*
>function();" which is a quite good fit, because the argument list is
>still left open, but it fixes the return type to some pointer type.
>Before calling that function, the function address is put into a
>function pointer of the correct type and invoked via that pointer. This
>model currently works fine (possibly by accident) on all architectures
>ghc supports except m68k.
>I developed a gcc patch that does not change the code generation for
>conforming programs but fixes this non-conforming use-case by always
>taking the actual return type in the call expression into account, even
>if the function declaration to be called is known. Please comment
>whether such a patch has any chance to be applied to either gcc
>or gcc in Debian.
Without looking at the patch this is already how GCC should behave for all targets.
> Michael Karcher