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Message-ID: <20140805170942.GG1674@brightrain.aerifal.cx>
Date: Tue, 5 Aug 2014 13:09:43 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: PATCH: don't call cleanup handlers after a regular return
from the thread start function
On Tue, Aug 05, 2014 at 06:51:34PM +0200, Jens Gustedt wrote:
> Don't call cleanup handlers after a regular return from the thread
> start function
>
> The chained list of cleanup handler function uses list items that are
> local to the respective function of a cleanup block. In case of a
> return out of the middle of a cleanup block, using these list items
> can lead to UB.
>
> POSIX lists three different cases in which a cleanup handler that is
> established on the cleanup stack has to be executed. Regular return
> from the thread start function is not among these cases.
>
> Linux manpages are more explicit and state:
>
> Clean-up handlers are not called if the thread terminates by
> performing a return from the thread start function.
>
> This patch aligns musl to that behavior.
Could you clarify why this patch is necessary? I think such a return
is explicitly UB:
"The effect of the use of return, break, continue, and goto to
prematurely leave a code block described by a pair of
pthread_cleanup_push() and pthread_cleanup_pop() functions calls is
undefined."
http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_cleanup_pop.html
I don't see why the thread start function should be treated as special
here.
Rich
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