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Date: Thu, 14 Jan 2016 17:17:11 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: Possible infinite loop in qsort()
On Tue, Jan 12, 2016 at 03:25:57PM +0300, Alexander Cherepanov wrote:
> On 2016-01-10 14:38, Markus Wichmann wrote:
> >On Sat, Jan 09, 2016 at 11:05:16PM -0500, Rich Felker wrote:
> >>On Sat, Jan 09, 2016 at 10:07:19AM +0100, Felix Janda wrote:
> >>>musl enforces that object sizes should not be greater than PTRDIFF_MAX.
> >>>See for example the discussion at
> >>>
> >>>http://www.openwall.com/lists/musl/2013/06/27/7
> >>>
> >>>So there will not be objects of size 3GB with musl on x32. Since the
> >>>Leonardo numbers grow slower than 2^n in general no overflow should
> >>>happen if "size" is valid. Otherwise, UB was invoked.
> >>
> >
> >OK. Might want to make that assumption a bit more prominent, because
> >this is the first time I've ever heard about it, but OK, no objects >2GB
> >on 32-bit archs.
>
> Yeah, I don't see it in the doc. Did I miss it?
The documentation is incomplete; in particular, the part that would
cover things like this has not been written at all and exists just in
my head (and to a lesser extent as implied from commit messages and
mailing list threads). :-)
> If it neither works nor documented as a limit I'd call it a bug.
An implementation is under no obligation to document the conditions
under which it's "out of memory" (ENOMEM). These are usually complex
and highly implementation specific.
> BTW the support in compilers for working with objects larger than
> half the address space is buggy -- see
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67999 . The same
> situation -- it neither works nor documented. Somewhat puzzling...
The only bug here is that it's not documented. "Supporting" such
objects without making ptrdiff_t a 64-bit type is an intolerably bad
QoI issue.
Rich
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