From: Jeff King <peff@peff.net>
Date: Tue, 03 Jul 2012 03:45:03 GMT
Subject: Re: bug: "fatal: cannot pread pack file", version 1.7.5.4
Message-ID: <20120703032345.GA7143@sigill.intra.peff.net>
In-Reply-To: <m2vci5n5r5.fsf@igel.home>

On Tue, Jul 03, 2012 at 12:43:42AM +0200, Andreas Schwab wrote:

> Jeff King <peff@peff.net> writes:
> 
> > It's very odd for pread to report ENOENT (since it is always operating
> > on an already-opened file descriptor).
> 
> It doesn't, but gettext will clobber errno:
> 
> 		n = pread(pack_fd, inbuf, n, from);
> 		if (n < 0)
> 			die_errno(_("cannot pread pack file"));
> 
> There is nothing that saves errno.  This isn't limited to i18n though,
> any function call in the arguments may potentially clobber errno.

That's horribly lame of gettext. I don't expect arbitrary functions to
save errno, but when the entire purpose of a function is to be a
non-intrusive wrapper to massage messages to the user, it seems kind of
evil to overwrite errno. Isn't the whole point of calling it "_" that
you don't want to or have to notice it?

Can we do something like this to get around it?

diff --git a/gettext.h b/gettext.h
index 57ba8bb..b7c3ae5 100644
--- a/gettext.h
+++ b/gettext.h
@@ -44,7 +44,10 @@ extern int use_gettext_poison(void);
 
 static inline FORMAT_PRESERVING(1) const char *_(const char *msgid)
 {
-	return use_gettext_poison() ? "# GETTEXT POISON #" : gettext(msgid);
+	int saved_errno = errno;
+	const char *r = use_gettext_poison() ? "# GETTEXT POISON #" : gettext(msgid);
+	errno = saved_errno;
+	return r;
 }
 
 static inline FORMAT_PRESERVING(1) FORMAT_PRESERVING(2)