Re: Handling of main() function for freestanding

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Sep 29, 2022 at 08:00:15AM +0200, Richard Biener via Gcc wrote:
> On Wed, Sep 28, 2022 at 10:17 PM Jonathan Wakely via Gcc
> <gcc@gcc.gnu.org> wrote:
> >
> > As part of implementing a C++23 proposal [1] to massively increase the
> > scope of the freestanding C++ standard library some questions came up
> > about the special handling of main() that happens for hosted
> > environments.
> >
> > As required by both C++ (all versions) and C (since C99), falling off
> > the end of the main() function is not undefined, the compiler is
> > required to insert an implicit 'return 0' [2][3]. However, this
> > special handling only applies to hosted environments. For freestanding
> > the return type or even the existence of main is
> > implementation-defined.
>  ^^^^^^^^^^^^^^^^^^^^^^
> 
> so just document that 'int main(int, char **)' is special to GCC even in
> freestanding environments and do not emit -Wreturn-type diagnostics?
> I think that's entirely reasonable (but of course make sure to add
> an implicit return 0; then as well)

-fspecial-main is weirdly named, I wonder if we couldn't do the
above by default and have -fno-builtin-main turn that special behavior
off (in that case then don't append return 0 and emit -Wreturn-type
diagnostics).  Not all our builtins are about whether we expand them inline, but
about whether we apply special handling to those functions, assume special
properties etc.  Just -fno-builtin shouldn't imply -fno-builtin-main...

	Jakub