From: Rich Felker <dalias@aerifal.cx>
To: musl@lists.openwall.com
Subject: Re: Use of size_t and ssize_t in mseek
Date: Thu, 4 Jul 2013 11:26:54 -0400 [thread overview]
Message-ID: <20130704152654.GP29800@brightrain.aerifal.cx> (raw)
In-Reply-To: <20130704111054.GY15323@port70.net>
On Thu, Jul 04, 2013 at 01:10:54PM +0200, Szabolcs Nagy wrote:
> * Rich Felker <dalias@aerifal.cx> [2013-07-04 04:12:45 -0400]:
> > On Thu, Jul 04, 2013 at 09:11:29AM +0200, Jens Gustedt wrote:
> > > > qsort_s can store the comparison function and context in TLS, and then
> > > > pass to qsort a comparison function that grabs these from TLS and
> > > > calls the original comparison function with the context pointer. This
> > > > is valid assuming qsort does not run the comparisons in new threads.
> > >
> > > sure, but for an execution of qsort_s this would have a lot of
> > > indirections and a call to TLS for every comparison. For performance
> > > sensible functions like this, this doesn't sound very attractive.
> >
> > If it's inside musl, the TLS dereference is very cheap on most archs:
> > it's just a constant offset from the thread pointer. Same if the code
> > were static linked in the main program. Otherwise, if it's a dynamic
> > library, then yes it would be fairly costly, like you say.
>
> it seems to me that if a qsort_s call sets the tls and then before
> the callee reads that pointer a signal interrupts with a handler that
> calls qsort_s again then the tls is overwritten by another pointer
>
> so you lose signal-safety with the tls design
As long as qsort_s saves the old value from TLS on its stack and
restores it before returning, you don't lose AS-safety except in the
case of a longjmp out of qsort_s. But I agree this is a negative
aspect of the possible design.
Rich
next prev parent reply other threads:[~2013-07-04 15:26 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-27 3:52 Matthew Fernandez
2013-06-27 4:10 ` Rich Felker
2013-06-27 4:16 ` Matthew Fernandez
2013-06-27 4:23 ` Rich Felker
2013-06-27 4:31 ` Matthew Fernandez
2013-06-27 15:34 ` Rich Felker
2013-06-28 0:49 ` Matthew Fernandez
2013-06-28 1:22 ` Rich Felker
2013-06-28 1:34 ` Matthew Fernandez
2013-06-28 1:48 ` Rich Felker
2013-06-28 1:56 ` Matthew Fernandez
2013-06-29 4:13 ` Rich Felker
2013-06-29 13:38 ` Matthew Fernandez
2013-06-29 14:17 ` Rich Felker
2013-06-29 14:56 ` Jens Gustedt
2013-06-29 15:48 ` Rich Felker
2013-06-29 16:01 ` Jens Gustedt
2013-06-29 16:13 ` Rich Felker
2013-06-29 16:39 ` Jens Gustedt
2013-07-04 1:28 ` Rich Felker
2013-07-04 6:11 ` Jens Gustedt
2013-07-04 6:37 ` Rich Felker
2013-07-04 7:11 ` Jens Gustedt
2013-07-04 8:12 ` Rich Felker
2013-07-04 8:45 ` Jens Gustedt
2013-07-04 15:24 ` Rich Felker
2013-07-04 11:10 ` Szabolcs Nagy
2013-07-04 11:58 ` Jens Gustedt
2013-07-04 15:26 ` Rich Felker [this message]
2013-06-27 10:35 ` Szabolcs Nagy
2013-06-27 15:05 ` Rich Felker
2013-06-27 16:47 ` Rich Felker
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