From: "H.J. Lu" <hjl.tools@gmail.com>
To: "Carlos O'Donell" <carlos@redhat.com>
Cc: Florian Weimer <fweimer@redhat.com>,
Szabolcs Nagy <nsz@port70.net>, Jan Beulich <JBeulich@suse.com>,
Rich Felker <dalias@libc.org>,
Binutils <binutils@sourceware.org>,
gnu-gabi@sourceware.org
Subject: Re: RFC: Add SHT_GNU_PHDRS
Date: Mon, 01 Jan 2018 00:00:00 -0000 [thread overview]
Message-ID: <CAMe9rOrW38N+2H-bVGrFaZYiHoRSSzCvzaazuyHFDE24rxDRUQ@mail.gmail.com> (raw)
In-Reply-To: <73bd396c-43be-2922-fce4-17ee835d862e@redhat.com>
On Thu, Sep 27, 2018 at 6:07 AM, Carlos O'Donell <carlos@redhat.com> wrote:
> On 9/27/18 8:57 AM, Florian Weimer wrote:
>> * H. J. Lu:
>>
>>> On Thu, Sep 27, 2018 at 5:42 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>>> * H. J. Lu:
>>>>
>>>>> On Thu, Sep 27, 2018 at 3:35 AM, Szabolcs Nagy <nsz@port70.net> wrote:
>>>>>> an alloc .phdr section covering the program headers solves
>>>>>> this problem. if sections are not required for segments
>>>>>> then simply the linker should ensure that there is always
>>>>>> a load segment covering the program headers, possibly
>>>>>> without containing any sections, however elf says
>>>>>> "An object file segment contains one or more sections".
>>>>>>
>>>>>> i don't understand why a zero-size section is enough, what
>>>>>> if phdr > pagesize? will that get covered by the load
>>>>>> segment that is created for the zero-size section?
>>>>>
>>>>> Linker must keep this zero-size section in output and
>>>>> create a PT_LOAD segment to cover it even if it is
>>>>> the only SHF_ALLOC section in the PT_LOAD segment.
>>>>
>>>> Based on Szabolcs' comment, I don't think the section can be zero-sized.
>>>>
>>>
>>> Why can't we put a zero-size section in a PT_LOAD segment?
>>> Of course, we need to change linker to do it.
>>
>> I'm now under the impression that the bits that are PT_LOAD'ed all need
>> to be covered by (allocated) sections. A zero-sized section doesn't
>> cover anything, so it doesn't address this requirement of the ELF
It depends on how we define it. I did experiment SHT_GNU_PHDRS
to cover the whole program header. But other tools don't expect a
section covering the program header.
>> specification.
>
> I agree. What we did in the past by relying on phdrs to be accidentally
> in the first PT_LOAD segment always irked me as bad design.
>
> If we need access to program header we need clear semantics for doing so,
> not hackish kludges to force the linker to get it onto a page that also
> happened to be mapped. This is just poor engineering on our part.
>
My current dummy program property note section sounds much better
now :-).
--
H.J.
next prev parent reply other threads:[~2018-09-27 13:21 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-01 0:00 H.J. Lu
[not found] ` <CAORpzuOWtHeqBLEE+MMN4-TZyp6Z1r-MdmyNv7Zj-BhxMstr=g@mail.gmail.com>
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Jan Beulich
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Szabolcs Nagy
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Michael Matz
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Michael Matz
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Rich Felker
2018-01-01 0:00 ` H.J. Lu [this message]
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` H.J. Lu
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