Date: Sat, 9 Oct 2010 16:08:50 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Jilles Tjoelker <jilles@stack.nl> Cc: freebsd-standards@freebsd.org Subject: Re: standards/151316: lib/libc/string/strerror.c r1.9 breaks POSIX Message-ID: <20101009130850.GY2392@deviant.kiev.zoral.com.ua> In-Reply-To: <201010091240.o99Ce7AM048178@freefall.freebsd.org>
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On Sat, Oct 09, 2010 at 12:40:07PM +0000, Jilles Tjoelker wrote:
> The following reply was made to PR standards/151316; it has been noted by GNATS.
>
> From: Jilles Tjoelker <jilles@stack.nl>
> To: Jeremy Huddleston <jeremyhu@apple.com>
> Cc: freebsd-gnats-submit@FreeBSD.org
> Subject: Re: standards/151316: lib/libc/string/strerror.c r1.9 breaks POSIX
> Date: Sat, 9 Oct 2010 14:37:31 +0200
>
> On Fri, Oct 08, 2010 at 04:28:55PM +0000, Jeremy Huddleston wrote:
> > >Number: 151316
> > >Category: standards
> > >Synopsis: lib/libc/string/strerror.c r1.9 breaks POSIX
>
> > >Description:
> > r1.9 of strerror.c did the following (from the changeslog)
>
> > strerror()'s semantics have changed slightly such that an argument of
> > 0 is now considered invalid and errno is set to EINVAL.
>
> > This introduces a regression in SUS conformance.
>
> Please explain why. As far as I understand, 0 is not a valid error
> number, and therefore it is appropriate to set errno = EINVAL while
> still returning a string.
>
> Hints to 0 being an invalid error number are the requirement that all E*
> constants from <errno.h> be positive and the requirement that no
> POSIX-defined function shall set errno to 0.
>
> If I'm wrong, please provide a reference such as to a specific section
> in the standard.
>
> In any case, this is of little practical effect since few programs check
> the value of errno set by strerror(). If the patch is accepted,
> sys_errlist[0] will probably be changed to "Unknown error: 0" so the
> only difference is errno set by strerror().
>
> > >How-To-Repeat:
>
> > >Fix:
> > In strerror.c's strerror_r
> > - if (errnum < 1 || errnum >= sys_nerr) {
> > + if (errnum < 0 || errnum >= sys_nerr) {
>
> > And here's a man page change:
>
> > @@ -110,7 +118,7 @@
> > .Er EINVAL
> > as a warning.
> > Error numbers recognized by this implementation fall in
> > -the range 0 <
> > +the range 0 <=
> > .Fa errnum
> > <
> > .Fa sys_nerr .
The often-used idiom is
printf("Error %d %s\n", errno, strerror(errno));
In case of errno == 0 you get
Error 0: Unknown error
or something else depending on the order of evaluation of the arguments.
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