From: Michael Matz <matz@suse.de>
To: Szabolcs Nagy <nsz@port70.net>
Cc: "H.J. Lu" <hjl.tools@gmail.com>, Alan Modra <amodra@gmail.com>,
gnu-gabi@sourceware.org
Subject: Re: Specify how undefined weak symbol should be resolved in executable
Date: Fri, 01 Jan 2016 00:00:00 -0000 [thread overview]
Message-ID: <alpine.LSU.2.20.1602231716470.20277@wotan.suse.de> (raw)
In-Reply-To: <20160223154437.GA29662@port70.net>
Hi,
On Tue, 23 Feb 2016, Szabolcs Nagy wrote:
> libgcc/gthr-posix.h checks 'multi-threadedness' by looking
> at a weakref (if it's zero then single-threaded execution
> is assumed).
>
> on glibc the weakref is __pthread_key_create nowadays,
> but on other systems or older libgcc it's pthread_cancel.
Yep, that's the one.
> so the address of this weakref is taken, the other pthread weakrefs are
> called only if this weakref was non-zero.
>
> i'm not sure how the proposed changes affect this use-case,
Some of the variants will make this use-case work also for non-PIC
executables, at the expense of one more unsharable .text page on some
architectures (the one where this adress-checking takes place).
> but this way of deciding single-threadedness is broken and a bug that
> gcc should eventually fix. (e.g. a static linked multi-threaded c++
> application may not have a pthread_cancel symbol defined and thus
> libstdc++ may not use locks where necessary or crash when pthread_cancel
> is defined but other weakrefs are not).
Yep, that's one problem of our current behaviour with addresses of weak
symbols on non-PIC.
Ciao,
Michael.
next prev parent reply other threads:[~2016-02-23 16:21 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-01 0:00 H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Alan Modra
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` Szabolcs Nagy
2016-01-01 0:00 ` Michael Matz [this message]
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Alan Modra
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Alan Modra
2016-01-01 0:00 ` Carlos O'Donell
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
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