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Date: Wed, 13 Apr 2022 10:05:33 -0400
From: Rich Felker <dalias@libc.org>
To: Natanael Copa <ncopa@alpinelinux.org>
Cc: "Gary E. Miller" <gem@rellim.com>, musl@lists.openwall.com
Message-ID: <20220413140532.GT7074@brightrain.aerifal.cx>
References: <20220412134355.59bd920e@spidey.rellim.com>
 <20220413142432.311e20f5@ncopa-desktop.lan>
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User-Agent: Mutt/1.5.21 (2010-09-15)
Subject: Re: [musl] *strerror_r() bug in musl

On Wed, Apr 13, 2022 at 02:24:32PM +0200, Natanael Copa wrote:
> On Tue, 12 Apr 2022 13:43:55 -0700
> "Gary E. Miller" <gem@rellim.com> wrote:
> 
> > Yo All!
> 
> Hi!
> 
> > 
> > I'm new to the list.  I;ve been trying to report a musl bug on #musl since
> > last Friday, but no one seems to live there.
> > 
> > musl (all versions) has a bug in strerror_r().
> > 
> > The musl reference manual says of _GNUSOURCE:
> > 
> >     _GNU_SOURCE (or _ALL_SOURCE)
> > 
> >     Adds everything above, plus interfaces modeled after GNU libc
> >     extensions and interfaces for making use of Linux-specific features.
> > 
> > I take that to mean that when _GNU_SOURCE is used to compile code with musl
> > that the results will behave as GNU libc (glinc).
> 
> Well, as other has mentioned. GNU libc has a non-compliant version of
> strerror_r.
> 
> ....
>  
> > When _GNU_SOURCE is defined with glibc, then strerror_r() returns a char *.
> 
> I have met this in multiple places the last decade. The usual way to
> fix it is to also check for GNU libc in addition to _GNU_SOURCE.
> 
> #if defined (__GLIBC__) && defined (_GNU_SOURCE)
> 	/* non-standard GLIBC exception */
> #else
> 	/* standard behavior for everything else */
> #endif

That, or probe for the signature with a configure-style check and use
the result of that, as in

#ifdef HAVE_GNU_STRERROR_R
// handle the GNU version
#else
// code written to the standard
#endif

or, even better, wrapping strerror_r in a translation unit that begins
with

#undef _GNU_SOURCE
#define _POSIX_C_SOURCE 200809L

or similar so that you always get the standard one, and calling your
wrapper instead.

Rich