Message-ID: <e262ea00-a027-9073-812e-7e034d75e718@infradead.org>
Date:   Tue, 14 Mar 2023 19:34:11 -0700
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Subject: Re: [PATCH] ELF: document some de-facto PT_* ABI quirks
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To:     Alexey Dobriyan <adobriyan@gmail.com>, akpm@linux-foundation.org
Cc:     linux-kernel@vger.kernel.org,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>
References: <2acb586c-08a9-42d9-a41e-7986cc1383ea@p183>
From:   Randy Dunlap <rdunlap@infradead.org>
In-Reply-To: <2acb586c-08a9-42d9-a41e-7986cc1383ea@p183>
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Hi,

[adding linux-doc for other interested parties]


On 3/14/23 10:02, Alexey Dobriyan wrote:
> Turns out rules about PT_INTERP, PT_GNU_STACK and PT_GNU_PROPERTY
> segment headers are slightly different.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
> 
>  Documentation/ELF/ELF.rst |   28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> new file mode 100644
> --- /dev/null
> +++ b/Documentation/ELF/ELF.rst
> @@ -0,0 +1,28 @@
> +.. SPDX-License-Identifier: GPL-2.0

According to Documentation/doc-guide/sphinx.rst, "=" underlines are used
for chapters (by convention).

And could the document have a title, like:

=========================
ELF header usage in Linux
=========================

(I just made that up. Feel free to change it. :)

Also, the .rst file should be added to some chapter in the current
documentation tree, such as under "Other documentation", so add this file name
to Documentation/staging/index.rst. In fact this file could live in
Documentation/staging instead of in Documentation/ELF/ (IMO of course).


> +
> +Definitions
> +===========
> +
> +"First" program header is the one with the smallest offset in the file:
> +e_phoff. "Last" program header is the one with the biggest offset:
> +e_phoff + (e_phnum - 1) * sizeof(Elf_Phdr).
> +
> +PT_INTERP
> +=========
> +
> +First PT_INTERP program header is used to locate the filename of ELF
> +interpreter. Other PT_INTERP headers are ignored (since Linux 2.4.11).
> +
> +PT_GNU_STACK
> +============
> +
> +Last PT_GNU_STACK program header defines userspace stack executability
> +(since Linux 2.6.6). Other PT_GNU_STACK headers are ignored.
> +
> +PT_GNU_PROPERTY
> +===============
> +
> +ELF interpreter's last PT_GNU_PROPERTY program header is used (since
> +Linux 5.8). If interpreter doesn't have one, then the last PT_GNU_PROPERTY
> +program header of an executable is used. Other PT_GNU_PROPERTY headers
> +are ignored.

Thanks.
-- 
~Randy