From: Joe Groff <jgroff@apple.com>
To: Cary Coutant <ccoutant@gmail.com>
Cc: "H.J. Lu" <hjl.tools@gmail.com>, Binutils <binutils@sourceware.org>
Subject: Re: Preventing preemption of 'protected' symbols in GNU ld 2.26
Date: Mon, 28 Mar 2016 22:41:00 -0000 [thread overview]
Message-ID: <3AB69E51-F694-4CD0-862B-33F56CF4630F@apple.com> (raw)
In-Reply-To: <CAJimCsGDoYVWP4WLB-vu6Gr3Lnh0DoYYrWPZYgC3MKJ7Jv0oqQ@mail.gmail.com>
> On Mar 28, 2016, at 3:38 PM, Cary Coutant <ccoutant@gmail.com> wrote:
>
>>>> Did you look at what the costs were in startup time and dirty pages by using
>>>> copy relocations? What do you do if the size of the definition changes in a
>>>> new version of the library?
>>>
>>> There wouldn't be a measurable cost in dirty pages; the copied objects
>>> are simply allocated in bss in the executable.
>>
>> Wouldn't references to the symbol from within the .so need to be relocated to reference the now-canonical copy in the executable?
>
> No, references from within the .so would have always used the GOT.
> Non-protected global symbols in a shared library are still
> pre-emptible, so they are always indirect, and there's always a
> dynamic relocation for the GOT entry. Whether the prevailing
> definition winds up in the executable or the shared library, the
> dynamic loader still has to bind the symbol and apply the relocation.
Ah, right, ELF symbols are preemptible by default, so you'd already be dirtying any pages containing data-to-data references to the symbol regardless.
-Joe
next prev parent reply other threads:[~2016-03-28 22:41 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-24 0:00 Joe Groff
2016-03-24 0:45 ` H.J. Lu
2016-03-24 0:52 ` Joe Groff
2016-03-24 1:25 ` H.J. Lu
2016-03-24 15:01 ` Cary Coutant
2016-03-24 15:07 ` H.J. Lu
2016-03-24 16:06 ` Cary Coutant
2016-03-24 16:42 ` H.J. Lu
2016-03-24 16:56 ` Cary Coutant
2016-03-24 17:05 ` H.J. Lu
2016-03-24 17:06 ` Joe Groff
2016-03-24 17:09 ` H.J. Lu
2016-03-24 18:31 ` Cary Coutant
2016-03-27 16:26 ` Rafael Espíndola
2016-03-28 12:12 ` H.J. Lu
2016-03-28 22:12 ` Cary Coutant
[not found] ` <BC969B3B-87A2-4238-90C8-DA2E166707AF@apple.com>
2016-03-28 17:03 ` Joe Groff
2016-03-28 17:17 ` H.J. Lu
2016-03-28 22:22 ` Cary Coutant
2016-03-28 22:24 ` Joe Groff
2016-03-28 22:38 ` Cary Coutant
2016-03-28 22:41 ` Joe Groff [this message]
2016-03-28 23:21 ` Alan Modra
2016-03-29 0:29 ` Cary Coutant
2016-03-29 15:44 ` H.J. Lu
2016-03-29 12:40 ` Maciej W. Rozycki
[not found] <AB592ABD-D6D7-4D2F-A0D6-45738F168DC4@apple.com>
2016-03-29 19:31 ` Fwd: " Joe Groff
2016-03-29 19:33 ` H.J. Lu
2016-03-29 19:36 ` Joe Groff
2016-03-29 19:43 ` H.J. Lu
2016-03-29 19:51 ` Joe Groff
2016-03-29 19:54 ` H.J. Lu
2016-03-29 22:05 ` H.J. Lu
2016-03-30 1:44 ` Alan Modra
2016-03-30 1:46 ` Cary Coutant
2016-03-30 4:04 ` Jeff Law
2016-03-30 7:20 ` Cary Coutant
2016-03-30 7:34 ` Cary Coutant
2016-03-30 14:44 ` Alan Modra
2016-03-31 0:45 ` Cary Coutant
2016-03-31 0:40 ` Cary Coutant
2016-03-31 0:53 ` Jeff Law
2016-03-31 13:27 ` Ramana Radhakrishnan
2016-03-31 15:05 ` H.J. Lu
2016-04-15 16:10 ` Szabolcs Nagy
2016-04-01 19:51 ` Jeff Law
2016-04-02 2:53 ` Alan Modra
2016-04-15 16:16 H.J. Lu
2016-04-15 16:36 ` Jeff Law
2016-04-15 16:45 ` H.J. Lu
2016-04-15 16:43 ` Szabolcs Nagy
2016-04-15 23:59 ` Maciej W. Rozycki
2016-04-16 1:08 ` Szabolcs Nagy
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