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From: Jens Gustedt <jens.gustedt@inria.fr>
To: musl@lists.openwall.com
Subject: Re: [musl] direct coding of asctime_r
Date: Thu, 27 Aug 2020 11:27:59 +0200	[thread overview]
Message-ID: <20200827112759.7e04abd3@inria.fr> (raw)
In-Reply-To: <20200824161400.GG3265@brightrain.aerifal.cx>

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Rich,

on Mon, 24 Aug 2020 12:14:00 -0400 you (Rich Felker <dalias@libc.org>)
wrote:

> I'm not *strongly* opposed to this, but my reasoning is fairly much in
> line with the POSIX side, that these interfaces are legacy/deprecated,
> and in general musl practice is to choose maximum simplicity over
> size/performance optimality for deprecated/legacy or junk interfaces.
> 
> In particular, asctime[_r] formats dates in a legacy US format,
> whereas modern applications should be using either ISO date format or
> a locale-specific format.

But which is also a format used by the language itself (or refered to)
by `__TIME__` and similar macros.

> Note that ISO C specifies asctime in terms of a particular printf
> format string, meaning the results are well-defined for any values
> that don't overflow the specified buffer, even if they are somewhat
> nonsensical.

I don't think so. The general rules for valid arguments to C library
functions always apply, so according to 7.1.4 calls to the functions
with values that are outside the specified ranges for the type have
UB.

In the <time.h> header the only exception from this rule seems to be
`mktime`, which makes such exceptions explicit and says how the
argument is normalized if it is not in the ranges as specified.

The sample code that I posted does range checks with simple means that
never results in unbounded UB and always returns a string that is null
terminated. I would think that this is reasonable behavior.

Jens

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  reply	other threads:[~2020-08-27  9:28 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-23  8:24 Jens Gustedt
2020-08-23  9:33 ` Alexander Monakov
2020-08-23  9:56   ` Jens Gustedt
2020-08-23 11:08     ` Alexander Monakov
2020-08-24 16:14 ` Rich Felker
2020-08-27  9:27   ` Jens Gustedt [this message]
2020-08-27 14:03     ` Rich Felker
2020-08-27 14:24       ` Jens Gustedt

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