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Re: [RFC][PATCH] Check ELF relocs after opening all all input files
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Alan Modra <amodra at gmail dot com>
- Cc: Nick Clifton <nickc at redhat dot com>, Binutils <binutils at sourceware dot org>
- Date: Wed, 20 Apr 2016 17:39:41 -0700
- Subject: Re: [RFC][PATCH] Check ELF relocs after opening all all input files
- Authentication-results: sourceware.org; auth=none
- References: <20160419134956 dot GA12310 at intel dot com> <57165642 dot 1070808 at redhat dot com> <CAMe9rOrydGcortz2AsujVSQYZCRbSPsi7CFQRnA6ZZiicbUvTA at mail dot gmail dot com> <20160419232457 dot GB20119 at bubble dot grove dot modra dot org>
On Tue, Apr 19, 2016 at 4:24 PM, Alan Modra <firstname.lastname@example.org> wrote:
> On Tue, Apr 19, 2016 at 11:03:15AM -0700, H.J. Lu wrote:
>> On Tue, Apr 19, 2016 at 9:01 AM, Nick Clifton <email@example.com> wrote:
>> > Hi H.J.
>> >> Delaying checking ELF relocations until opening all input files so
>> >> that symbol information is final when relocations are checked. This
>> >> is only enabled for x86 targets.
>> >> Any comments, feedbacks?
>> > What benefit is gained by doing this ? I would guess that it is connected
>> > with symbols changing type and/or visibility and/or protected status, but
>> > it would be nice to know what you are hoping to achieve.
>> Yes, this change is motivated by that discussion. Currently backend
>> check_relocs doesn't have the final information on symbols. A better
>> linker can provide better diagnostics in check_relocs if symbol info is
> There are other benefits too. As it is the backend check_relocs
> functions do things like "maybe this symbol remains undefined so
> perhaps it needs a plt entry", and "maybe this symbol remains dynamic
> so perhaps it needs dynamic relocations". This complexity can
> disappear if all of those "maybe" cases are resolved.
The first phase of x86 backend is done. I will take a look to see if I can
remove some checks in x86 check_relocs when I have time.
> Now, if you run check_relocs even later, say at
> ldemul_before_allocation, after gc-sections has run, then all the
> reference counting code for plt and got relocs can be removed too.
I checked in:
Author: H.J. Lu <firstname.lastname@example.org>
Date: Wed Apr 20 17:12:46 2016 -0700
Remove x86 gc_sweep_hook
Since x86 backends never see the removed sections, there is no need
* elf32-i386.c (elf_i386_gc_sweep_hook): Removed.
* elf64-x86-64.c (elf_x86_64_gc_sweep_hook): Likewise.
Other reference counting code for plt and got relocs in x86 backend
has to stay for TLS optimization and GOT/PLT optimization.