From: "H.J. Lu" <hjl.tools@gmail.com>
To: Alan Modra <amodra@gmail.com>
Cc: "Martin Liška" <mliska@suse.cz>, Binutils <binutils@sourceware.org>
Subject: Re: [PATCH] elf: Don't load archive element after dynamic definition
Date: Wed, 2 Sep 2020 19:16:14 -0700 [thread overview]
Message-ID: <CAMe9rOrG0tAD2RnCgt-8Rq+i5zZZqkgu=JUTg11L=Xh455_Lzg@mail.gmail.com> (raw)
In-Reply-To: <20200903013137.GM15695@bubble.grove.modra.org>
On Wed, Sep 2, 2020 at 6:31 PM Alan Modra <amodra@gmail.com> wrote:
>
> On Wed, Sep 02, 2020 at 07:35:58AM -0700, H.J. Lu wrote:
> > On Wed, Sep 2, 2020 at 7:29 AM Alan Modra <amodra@gmail.com> wrote:
> > >
> > > On Wed, Sep 02, 2020 at 06:22:08AM -0700, H.J. Lu wrote:
> > > > > It's reasonably obvious that we need to load archive elements when
> > > > > they define IR referenced symbols, because the archive element might
> > > > > be an LTO object. What's not so obvious is whether loading of shared
> > > > > libraries should follow the same rule. I think they should, in order
> > > > > for LTO to get symbol resolution correct in corner cases. Basically
> > > > > LTO needs to know what shared libraries are loaded before
> > > > > recompilation. See commit a896df97b952 log comments.
> > > >
> > > > There is dynamic_def for this purpose.
> > >
> > > Your patch doesn't make changes to ld/plugin.c to inform LTO of the
> > > availability of these symbols. And if you did, then how does the
> > > linker work out whether or not the LTO recompilation depended on those
> > > symbols? If it did change LTO recompilation then you had better
> > > ensure the library really is loaded. By the time you work all of that
> > > out, if it is even possible, your patch will likely be very
> > > complicated indeed.
> >
> > A testcase?
>
> What don't you understand from my emails in this thread? I suggest
> you look at what happened with the testcase in PR26314, in regard to
> my comment
> The lto recompilation didn't see symbol references from libbfd.so and
> variables like _xexit_cleanup are made local in the recompiled
> objects. Oops, two copies of them.
A testcase?
> That's critical in understanding why LTO needs to know about symbols
> from shared libraries before LTO recompilation.
>
Linker is complicated and LTO makes it even more complicated.
Without a testcase, we can't be sure that the bug is really fixed
nor we can be sure it won't regress.
--
H.J.
next prev parent reply other threads:[~2020-09-03 2:16 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-25 17:28 H.J. Lu
2020-08-27 13:53 ` Alan Modra
2020-08-27 14:05 ` H.J. Lu
2020-08-28 1:58 ` Alan Modra
2020-08-28 12:53 ` H.J. Lu
2020-08-28 14:49 ` Alan Modra
2020-08-28 14:50 ` H.J. Lu
2020-09-02 6:52 ` Martin Liška
2020-09-02 8:12 ` Alan Modra
2020-09-02 11:56 ` H.J. Lu
2020-09-02 13:05 ` Alan Modra
2020-09-02 13:22 ` H.J. Lu
2020-09-02 14:29 ` Alan Modra
2020-09-02 14:35 ` H.J. Lu
2020-09-03 1:31 ` Alan Modra
2020-09-03 2:16 ` H.J. Lu [this message]
2020-09-03 6:07 ` Alan Modra
2020-09-03 11:34 ` H.J. Lu
2020-09-04 7:25 ` Alan Modra
2020-09-04 11:06 ` H.J. Lu
2020-09-08 5:42 ` Alan Modra
2020-09-08 12:43 ` H.J. Lu
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