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Date: Thu, 22 Jun 2023 19:37:22 -0400
From: "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
To: musl@...ts.openwall.com
Cc: Markus Wichmann <nullplan@....net>, Rich Felker <dalias@...c.org>
Subject: Re: [PATCH] [RFC] trap on invalid printf formats
Excerpts from Rich Felker's message of June 22, 2023 10:45 am:
> FWIW I don't think there are a lot of these cases left in the wild at
> all, but I'm not sure. it might be nice to do some distro-wide testing
> with this patch applied (which is what I had in mind posting it) and
> see if any problems are caught before really considering whether to
> pursue upstreaming it.
Unfortunately, it seems fairly widespread:
https://codesearch.debian.net/search?q=printf.*%5B%25%5DL%5Bud%5D+-package%3Agcc+-package%3Allvm*+path%3A.*%5C.c%24&literal=0
The most painful example:
#if defined(__OpenBSD__) || defined(__FreeBSD__) || defined(__APPLE_CC__) || defined(__APPLE__) || defined(ARGUS_SOLARIS)
sprintf (pbuf, "%llu", value);
#else
sprintf (pbuf, "%Lu", value);
#endif
(copied and pasted 17 times in the same file, of course)
I did some research and the most likely source of %Lu is the Linux
man-pages, which, before 1999 or thereabouts, said:
> • The optional character l (ell) specifying that a following d, i, o,
> u, x, or X conversion applies to a pointer to a long int or unsigned
> long int argument, or that a following n conversion corresponds to a
> pointer to a long int argument. Linux provides a non ANSI compliant
> use of two l flags as a synonym to q or L. Thus ll can be used in
> combination with float conversions. *This usage is, however, strongly
> discouraged.*
>
> • The character L specifying that a following e, E, f, g, or G
> conversion corresponds to a long double argument, or a following d, i,
> o, u, x, or X conversion corresponds to a long long argument. Note
> that long long is not specified in ANSI C and therefore not portable
> to all architectures.
Emphasis added. So, pre-C99, L was in fact the recommended modifier for
long long.
Cheers,
Alex.
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