GNU bug report logs - #7347
[PATCH] stat: do not rely on undefined behavior in printf formats

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From: Jim Meyering <jim <at> meyering.net>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 7347 <at> debbugs.gnu.org
Subject: bug#7347: [PATCH] stat: do not rely on undefined behavior in printf formats
Date: Sat, 06 Nov 2010 22:53:31 +0100

Paul Eggert wrote:
> I have not pushed this, as I understand you're trying to put out a
> release, but this fixes some portability bugs in 'stat', such that it
> was relying on undefined behavior, which presumably could cause
> 'stat' to dump core, or worse, on non-GNU platforms.
>
> The downside of this patch is that the "I" printf flag is now ignored.
> However, support for "I" wasn't working anyway (because of time stamp
> fractions), so this isn't much of a loss.  We can add proper "I"
> support later, if there's demand for it.
>
> Subject: [PATCH] stat: do not rely on undefined behavior in printf formats
>
> * src/stat.c (digits, printf_flags): New static vars.
> (make_format): New function.
> (out_string, out_int, out_uint, out_uint_o, out_uint_x):
> (out_minus_zero): Use it to avoid undefined behavior when invoking
> printf.
> (print_it): Check for invalid conversion specifications such as
> %..X and %1-X, which would otherwise rely on undefined behavior
> when invoking printf.
> * tests/misc/stat-nanoseconds: Check that the "I" printf flag
> doesn't mess up in the C locale, as it formerly did on non-GNU
> hosts.

Thanks for the patch!
I looked through it, applied it and tested it.
I see fixes (admittedly fringe, as you say, but still)
and don't see anything that might cause trouble, so go ahead and push it.
Nobody will miss the "I" flag.  I think I've never even seen it used.

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