Re: [PATCH] ELF: document some de-facto PT_* ABI quirks

Randy Dunlap
2023-03-15T02:34:21Z

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