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Date: Mon, 7 Mar 2022 11:42:39 -0500
From: James Y Knight <jyknight@...gle.com>
To: musl@...ts.openwall.com
Cc: "wangjianjian (C)" <wangjianjian3@...wei.com>
Subject: Re: basename with no parameter?
Note that the C2x standard intends to remove deprecated non-prototype
declarations, along with K&R-style non-prototype definitions. Empty
parens in a declaration will be treated as a zero-arg prototype, just as in
C++. (http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2841.htm).
Additionally, compilers may start emitting some default-on warnings for use
of these deprecated features even in pre-C2x language modes, although
that'd likely be suppressed for system headers.
It'd probably be a good idea to remove any such hacks which depend on
non-prototype declarations, to get ahead of these changes.
On Mon, Mar 7, 2022 at 8:19 AM Rich Felker <dalias@...c.org> wrote:
> On Mon, Mar 07, 2022 at 10:31:41AM +0800, wangjianjian (C) wrote:
> > Hi all,
> >
> > I find that the basename in string.h with _GNU_SOURCE in Musl
> > libc(Line 119):
> >
> > char *basename();
>
> This is not a declaration with no parameter. It's a declaration
> without any prototype.
>
> > The man page says that have two different version of basename
> > however both need one parameter, is this correct?
>
> No, that's documenting glibc. There is only one version of basename in
> musl and it's the standard one.
>
> The reason for the non-prototype declaration is explained in commit
> 37bb3cce4598c19288628e675eaf1cda6e96958f:
>
> omit declaration of basename wrongly interpreted as prototype in C++
>
> the non-prototype declaration of basename in string.h is an ugly
> compromise to avoid breaking 2 types of broken software:
>
> 1. programs which assume basename is declared in string.h and thus
> would suffer from dangerous pointer-truncation if an implicit
> declaration were used.
>
> 2. programs which include string.h with _GNU_SOURCE defined but then
> declare their own prototype for basename using the incorrect GNU
> signature for the function (which would clash with a correct
> prototype).
>
> however, since C++ does not have non-prototype declarations and
> interprets them as prototypes for a function with no arguments, we
> must omit it when compiling C++ code. thankfully, all known broken
> apps that suffer from the above issues are written in C, not C++.
>
> This was from 2012, so it might make sense to do something different
> now, like putting the correct prototype there and getting any programs
> it still clashes with fixed.
>
> Rich
>
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