From: Florian Weimer <fweimer@redhat.com>
To: Rich Felker <dalias@libc.org>
Cc: musl@lists.openwall.com
Subject: Re: aio_cancel segmentation fault for in progress write requests
Date: Sat, 08 Dec 2018 17:18:13 +0100 [thread overview]
Message-ID: <87in049em2.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <20181207201453.GH23599@brightrain.aerifal.cx> (Rich Felker's message of "Fri, 7 Dec 2018 15:14:53 -0500")
* Rich Felker:
> On Fri, Dec 07, 2018 at 09:06:18PM +0100, Florian Weimer wrote:
>> * Rich Felker:
>>
>> > I don't think so. I'm concerned that it's a stack overflow, and that
>> > somehow the kernel folks have managed to break the MINSIGSTKSZ ABI.
>>
>> Probably:
>>
>> <https://sourceware.org/bugzilla/show_bug.cgi?id=20305>
>> <https://sourceware.org/bugzilla/show_bug.cgi?id=22636>
>>
>> It's a nasty CPU backwards compatibility problem. Some of the
>> suggestions I made to work around this are simply wrong; don't take them
>> too seriously.
>>
>> Nowadays, the kernel has a way to disable the %zmm registers, but it
>> unfortunately does not reduce the save area size.
>
> How large is the saved context with the %zmm junk? I measured just
> ~768 bytes on normal x86_64 without it, and since 2048 is rounded up
> to a whole page (4096), overflow should not happen until the signal
> context is something like 3.5k (allowing ~512 bytes for TCB (~128) and
> 2 simple call frames).
I wrote a test to do some measurements:
<https://sourceware.org/ml/libc-alpha/2018-12/msg00271.html>
The signal handler context is quite large on x86-64 with AVX-512F,
indeed around 3.5 KiB. It is even larger on ppc64 and ppc64el
(~4.5 KiB), which I find somewhat surprising.
The cancellation test also includes stack usage from the libgcc
unwinder. Its stack usage likely differs between versions, so I should
have included that in the reported results.
Thanks,
Florian
next prev parent reply other threads:[~2018-12-08 16:18 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-07 12:52 Arkadiusz Sienkiewicz
2018-12-07 15:44 ` Rich Felker
2018-12-07 16:04 ` Arkadiusz Sienkiewicz
2018-12-07 16:52 ` Orivej Desh
2018-12-07 16:52 ` Rich Felker
2018-12-07 17:31 ` A. Wilcox
2018-12-07 18:26 ` Rich Felker
2018-12-07 19:05 ` A. Wilcox
2018-12-07 20:07 ` Rich Felker
2018-12-07 19:13 ` A. Wilcox
2018-12-07 20:21 ` Rich Felker
2018-12-07 20:35 ` Markus Wichmann
2018-12-07 21:12 ` Rich Felker
2018-12-07 22:51 ` A. Wilcox
2018-12-07 23:50 ` Rich Felker
2018-12-07 20:06 ` Florian Weimer
2018-12-07 20:14 ` Rich Felker
2018-12-08 16:18 ` Florian Weimer [this message]
2018-12-10 9:05 ` Arkadiusz Sienkiewicz
2018-12-12 0:36 ` Rich Felker
2018-12-17 14:21 ` Arkadiusz Sienkiewicz
2018-12-17 17:29 ` Rich Felker
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