diff mbox series

[v2] ELF: document some de-facto PT_* ABI quirks

Message ID c4233c97-306c-4db8-9667-34fc31ec4aed@p183
State New
Headers
Series [v2] ELF: document some de-facto PT_* ABI quirks |

Commit Message

Alexey Dobriyan March 26, 2023, 4:49 p.m. UTC 
  Turns out rules about PT_INTERP, PT_GNU_STACK and PT_GNU_PROPERTY
program headers are slightly different.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

	v2: integrate into documentation build system

 Documentation/ELF/ELF.rst   |   32 ++++++++++++++++++++++++++++++++
 Documentation/ELF/index.rst |   10 ++++++++++
 Documentation/index.rst     |    1 +
 3 files changed, 43 insertions(+)

new file mode 100644

Comments

Randy Dunlap March 26, 2023, 7:51 p.m. UTC | #1 
Hi Alexey,

On 3/26/23 09:49, Alexey Dobriyan wrote:
> Turns out rules about PT_INTERP, PT_GNU_STACK and PT_GNU_PROPERTY
> program headers are slightly different.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
> 
> 	v2: integrate into documentation build system
> 
>  Documentation/ELF/ELF.rst   |   32 ++++++++++++++++++++++++++++++++
>  Documentation/ELF/index.rst |   10 ++++++++++
>  Documentation/index.rst     |    1 +
>  3 files changed, 43 insertions(+)

I'm not sure that ELF merits its own subdirectory or that each item here
should be a chapter,  but this fixes all of the issues that I pointed out. Thanks.

Reviewed-by: Randy Dunlap <rdunlap@infradead.org>

> new file mode 100644
> --- /dev/null
> +++ b/Documentation/ELF/ELF.rst
> @@ -0,0 +1,32 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=================================
> +Linux-specific ELF idiosyncrasies
> +=================================
> +
> +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.
> new file mode 100644
> --- /dev/null
> +++ b/Documentation/ELF/index.rst
> @@ -0,0 +1,10 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===
> +ELF
> +===
> +
> +.. toctree::
> +   :maxdepth: 1
> +
> +   ELF
> --- a/Documentation/index.rst
> +++ b/Documentation/index.rst
> @@ -113,6 +113,7 @@ to ReStructured Text format, or are simply too old.
>     :maxdepth: 1
>  
>     staging/index
> +   ELF/index
>  
>  
>  Translations
Jonathan Corbet March 29, 2023, 4:40 p.m. UTC | #2 
Alexey Dobriyan <adobriyan@gmail.com> writes:

> Turns out rules about PT_INTERP, PT_GNU_STACK and PT_GNU_PROPERTY
> program headers are slightly different.
>
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
>
> 	v2: integrate into documentation build system
>
>  Documentation/ELF/ELF.rst   |   32 ++++++++++++++++++++++++++++++++
>  Documentation/ELF/index.rst |   10 ++++++++++
>  Documentation/index.rst     |    1 +
>  3 files changed, 43 insertions(+)

I really don't want to add another top-level directory for a single
short file ... I'm trying to have fewer of those directories, not more.

This is essentially use-space ABI information; I think you should really
just drop a file into Documentation/userspace-api/.

Thanks,

jon
diff mbox series

Patch

--- /dev/null
+++ b/Documentation/ELF/ELF.rst
@@ -0,0 +1,32 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================
+Linux-specific ELF idiosyncrasies
+=================================
+
+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.
new file mode 100644
--- /dev/null
+++ b/Documentation/ELF/index.rst
@@ -0,0 +1,10 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+===
+ELF
+===
+
+.. toctree::
+   :maxdepth: 1
+
+   ELF
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -113,6 +113,7 @@  to ReStructured Text format, or are simply too old.
    :maxdepth: 1
 
    staging/index
+   ELF/index
 
 
 Translations