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Date: Wed, 21 Aug 2013 22:27:25 +0200
From: Jilles Tjoelker <jilles@stack.nl>
To: Sergey Kandaurov <pluknet@freebsd.org>
Subject: Re: svn commit: r254600 - head/lib/libutil
Message-ID: <20130821202725.GA4991@stack.nl>
References: <201308211646.r7LGk6eV051215@svn.freebsd.org>
 <5214F72B.7070006@freebsd.org> <20130821190309.GB52908@omg>
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Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
 src-committers@freebsd.org, Andrey Chernov <ache@freebsd.org>
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On Wed, Aug 21, 2013 at 11:03:10PM +0400, Sergey Kandaurov wrote:
> On Wed, Aug 21, 2013 at 09:21:47PM +0400, Andrey Chernov wrote:
> > On 21.08.2013 20:46, Sergey Kandaurov wrote:
> > >  	number = strtoumax(buf, &endptr, 0);
> > >  
> > > +	if (number == UINTMAX_MAX && errno == ERANGE) {
> > > +		return (-1);
> > > +	}

> > You need to reset errno before strtoumax() call (errno = 0), because any
> > of previous functions may left it as ERANGE.

> Thanks for pointing out.
> Does the patch look good?

> Index: expand_number.c
> ===================================================================
> --- expand_number.c     (revision 254600)
> +++ expand_number.c     (working copy)
> @@ -53,6 +53,8 @@
>         unsigned shift;
>         char *endptr;
>  
> +       errno = 0;
> +
>         number = strtoumax(buf, &endptr, 0);
>  
>         if (number == UINTMAX_MAX && errno == ERANGE) {
> 

This may cause the function to set errno=0 if it is successful, which is
not allowed for standard library functions from C and POSIX. There may
be a problem not only if expand_number() is standardized but also if it
is used in the implementation of a standard library function. The best
solution is to save and restore errno around this (if [ERANGE] is
detected, that is a valid errno value to keep).

In an application it is acceptable to set errno=0 without further ado.

-- 
Jilles Tjoelker