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From: Florian Weimer <fweimer@redhat.com>
To: Carlos O'Donell <carlos@redhat.com>
Cc: Jozef Lawrynowicz <jozef.l@mittosystems.com>,  gnu-gabi@sourceware.org
Subject: Re: [RFC] SHF_GNU_RETAIN ELF Section Flag
Date: Tue, 15 Sep 2020 14:55:05 +0200	[thread overview]
Message-ID: <87mu1ri4ie.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <f0776cec-c518-8951-afa1-1bfa7fc6bf75@redhat.com> (Carlos O'Donell's message of "Tue, 15 Sep 2020 08:50:00 -0400")

* Carlos O'Donell:

> On 9/15/20 8:37 AM, Florian Weimer via Gnu-gabi wrote:
>> * Jozef Lawrynowicz:
>> 
>>> On Tue, Sep 15, 2020 at 02:09:22PM +0200, Florian Weimer wrote:
>>>> * Jozef Lawrynowicz:
>>>>
>>>>> I'd like to propose a new ELF section flag, SHF_GNU_RETAIN, for addition
>>>>> to the GNU gABI.
>>>>>
>>>>> This flag instructs the linker to "retain" the section in the output
>>>>> file, even if garbage collection would remove it because it appears
>>>>> unused.
>>>>
>>>> How does this flag interaction with libraries (.a files)?
>>>
>>> If a section in a library has SHF_GNU_RETAIN set, and that library gets
>>> searched by the linker for some undefined symbol, then the
>>> SHF_GNU_RETAIN section will also be pulled into the program, and
>>> retained in the linked output file.
>> 
>> Sorry, that's not quite what I meant.  What happens if the .o file with
>> SHF_GNU_RETAIN in an .a library is not otherwise referenced and thus
>> never loaded by the link editor?  How would the link editor realize that
>> it is even there?
>
> Why would it be loaded?

Hypothetically: Because the ranlib section tells the link editor to load
it (so more specification updates are needed).

> Why does the link editor need to detect the presence of such a file?

To make SHF_GNU_RETAIN work with libraries.

I think without that, the same effect can be had today with
SHF_GROUP/SHT_GROUP, perhaps with an assembler-only change to implement
the .retain pseudo.

Thanks,
Florian
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  reply	other threads:[~2020-09-15 12:55 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 12:06 Jozef Lawrynowicz
2020-09-15 12:09 ` Florian Weimer
2020-09-15 12:31   ` Jozef Lawrynowicz
2020-09-15 12:37     ` Florian Weimer
2020-09-15 12:50       ` Carlos O'Donell
2020-09-15 12:55         ` Florian Weimer [this message]
2020-09-15 13:29           ` Jozef Lawrynowicz
2020-09-15 14:11             ` Carlos O'Donell
2020-09-15 16:52               ` Jozef Lawrynowicz
2020-09-16 12:58                 ` Carlos O'Donell
2020-09-16 13:11                 ` Florian Weimer
2020-09-16 13:46                   ` Michael Matz
2020-09-18 12:07                     ` Florian Weimer
2020-09-18 12:22                       ` Jozef Lawrynowicz
2020-09-18 18:09                         ` Florian Weimer
2020-09-16 14:13                   ` Jozef Lawrynowicz
2020-09-18 10:00                     ` Jozef Lawrynowicz
2020-09-18 18:11                       ` Florian Weimer
2020-09-21 12:42                         ` Michael Matz
2020-09-21 18:53                           ` Jozef Lawrynowicz

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