From: "H.J. Lu" <hjl.tools@gmail.com>
To: Szabolcs Nagy <nsz@port70.net>
Cc: Florian Weimer <fweimer@redhat.com>,
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: <CAMe9rOp6bN3Pp4Zc37cfjNKjah00zkzWC-5eEboeJZsbZUkC=g@mail.gmail.com> (raw)
In-Reply-To: <20180927103539.GJ10209@port70.net>
On Thu, Sep 27, 2018 at 3:35 AM, Szabolcs Nagy <nsz@port70.net> wrote:
> * Florian Weimer <fweimer@redhat.com> [2018-09-27 10:21:40 +0200]:
>> * Jan Beulich:
>> >>>> On 27.09.18 at 07:01, <fweimer@redhat.com> wrote:
>> >> * H. J. Lu:
>> >>
>> >>> I am proposing
>> >>>
>> >>> #define SHT_GNU_PHDRS 0x6ffffff4 /* Dummy section for program header */
>> >>>
>> >>> This is a special read-only SHF_ALLOC zero-size data section. It is the
>> >>> first output section, which will force a data PT_LOAD segment with program
>> >>> header before the code-only PT_LOAD segment,
>> >>
>> >> Is it actually a requirement in the ELF specification that all bits
>> >> loaded via segments are covered by sections as well?
>> >
>> > Hardly, because the presence of a section table isn't required
>> > in the first place in an executable (iirc).
>>
>> I think so too, and that is why I don't understand this section hack is
>> needed.
>
> if there is no read-only alloc section then the program
> headers are currently not part of a load segment.
> https://sourceware.org/bugzilla/show_bug.cgi?id=23428
>
> 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.
--
H.J.
next prev parent reply other threads:[~2018-09-27 12:38 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-01 0:00 H.J. Lu
2018-01-01 0:00 ` Carlos O'Donell
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 ` Florian Weimer
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu [this message]
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
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Carlos O'Donell
[not found] ` <CAORpzuOWtHeqBLEE+MMN4-TZyp6Z1r-MdmyNv7Zj-BhxMstr=g@mail.gmail.com>
2018-01-01 0:00 ` H.J. Lu
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