RFC: syntax for a section ordering file

[H.J. Lu]

On Wed, Apr 24, 2024 at 6:58 AM Nick Clifton <nickc@redhat.com> wrote:
>
> Hi H.J.  Hi Fangrui,
>
>    Is there a defined syntax for the contents of a section ordering file ?
>    IE one passed to the linker via the --section-ordering= option ?
>
>    I am attempting to take H.J.'s bfd linker text section ordering file

Thank you for doing it.

>    patch and extend it to cover other sections.  In doing so, I need to
>    be sure that I have the syntax right.
>
>    To my mind if the section ordering file contains the following:
>
>       # A comment
>      .text.hot .text.cold,.text.warm
>      .data.big
>      .data.small
>      .text.foo*
>
>    Then this should be roughly equivalent to:
>
>    SECTIONS
>    {
>      .text : {
>        *(.text.hot)
>        *(.text.cold)
>        *(.text.warm)
>        *(.text.foo*)
>        *(.text)
>        }
>      .data : {
>        *(.data.big)
>        *(.data.small)
>        *(.data)
>        }
>    }

This looks correct to me.


>    So all of the .text.<something> entries in the section ordering
>    file are placed at the start of the output .text section (even
>    if some of them occur after entries for other output sections)
>    and all of the .data.<something> entries are placed at the start
>    of the .data section.
>
>    This will require co-operation from the linker script to have
>    the "INCLUDE config.section-ordering-file" statements at the
>    correct places, but I think that it could work.
>
>    But obviously I want the option to be compatible with GOLD and
>    LLD and I could not find any clear definitions or examples of
>    the syntax used.

lld doesn't support  --section-ordering-file.  I tried different syntaxes
with gold.  Gold doesn't complain about any inputs.  But only

.text.yyy
.text.bar
.text.xxx
.text.foo

works and it doesn't support wildcards.  I think wildcards are useful.

--
H.J.