This is the mail archive of the
binutils@sourceware.org
mailing list for the binutils project.
Re: [ARM] PR ld/20608
- From: Christophe Lyon <christophe dot lyon at linaro dot org>
- To: gingold at adacore dot com, binutils at sourceware dot org
- Date: Mon, 3 Oct 2016 09:06:34 +0200
- Subject: Re: [ARM] PR ld/20608
- Authentication-results: sourceware.org; auth=none
- References: <CAKdteOafjnhgqshyDvk0Q5r_yT4cVgz11PrPi=ye5oOCNhQaHg@mail.gmail.com> <817f016e-b658-4719-a6c0-1a257f5ab406@redhat.com> <06383e06-769d-a484-e96d-8951cb8b699f@arm.com> <20160922232524.GB26008@bubble.grove.modra.org> <CAKdteObnYPXHi+fKMF3p0KNfRSM8LOOjG_yGpYBAqH_7_eiUZQ@mail.gmail.com>
Hi Tristan,
Is it OK to backport this patch to 2.27 ? 2.26?
Thanks,
Christophe
On 28 September 2016 at 01:57, Christophe Lyon
<christophe.lyon@linaro.org> wrote:
> Hi,
>
> Sorry for the delay, I've just committed the patch as approved by Nick.
>
> Tristan, is it OK to backport this patch to 2.27 ? 2.26 ?
>
> On 23 September 2016 at 01:25, Alan Modra <amodra@gmail.com> wrote:
>> On Thu, Sep 22, 2016 at 04:39:30PM +0100, Richard Earnshaw (lists) wrote:
>>> So this patch got me wondering. If the PLT slot is so far away that we
>>> need an indirect jump to get there, why don't we clone the PLT code
>>> sequence at the veneer location? As I recall there's nothing
>>> architectural about placing all the PLT slots together, it's just more
>>> convenient to do that. We could even have the clone in Thumb-2 code if
>>> that's appropriate, so that it's compatible with tail calls.
>>
>
> If there are multiple PLT slots for the same function,
> doesn't this break the uniqueness of a function pointer?
>
>> Yeah, that's what ppc64 does. It does have one downside in that
>> synthetic plt symbols are not so easy to add.
>>
>> /* FIXME: It would be very much nicer to put sym@plt on the
>> stub rather than on the glink branch table entry. The
>> objdump disassembler would then use a sensible symbol
>> name on plt calls. The difficulty in doing so is
>> a) finding the stubs, and,
>> b) matching stubs against plt entries, and,
>> c) there can be multiple stubs for a given plt entry.
>>
>> Solving (a) could be done by code scanning, but older
>> ppc64 binaries used different stubs to current code.
>> (b) is the tricky one since you need to known the toc
>> pointer for at least one function that uses a pic stub to
>> be able to calculate the plt address referenced.
>> (c) means gdb would need to set multiple breakpoints (or
>> find the glink branch itself) when setting breakpoints
>> for pending shared library loads. */
>>
>> We avoid the problem by enabling --emit-stub-syms by default.
>>
>> --
>> Alan Modra
>> Australia Development Lab, IBM