From: Alan Modra <amodra@gmail.com>
To: Nick Clifton <nickc@redhat.com>
Cc: hjl.tools@gmail.com, binutils@sourceware.org, siddhesh@redhat.com
Subject: Re: RFC: ld: Add --text-section-ordering-file (version 2)
Date: Fri, 26 Apr 2024 13:47:51 +0930 [thread overview]
Message-ID: <Zisq7xDI0IK27Nf3@squeak.grove.modra.org> (raw)
In-Reply-To: <87edat7g1e.fsf@redhat.com>
On Thu, Apr 25, 2024 at 02:01:01PM +0100, Nick Clifton wrote:
> Hi Guys,
>
> Attached is a patch to add a --section-ordering-file option to the BFD
> linker. It is based upon H.J.'s original patch, but extended so that
> it will work with multiple output sections.
>
> There are a couple of points that I feel I should highlight:
>
> * The option only works in conjunction with a modified linker script.
>
> In particular the script must have: "INCLUDE section-ordering-file"
> statements in it, wherever it wants section ordering to be allowed.
> This statement can appear multiple times in a linker script,
> although it would not make sense to have it appear more than once in
> any given output section. Here is an example:
>
> SECTIONS
> {
> .text : {
> INCLUDE section-ordering-file
> *(.text)
> }
> .data : {
> INCLUDE section-ordering-file
> *(.data)
> }
> }
>
> * H.J's original version allowed for linker script like
> "filename(section)" syntax to be used to name sections, eg:
> "*(.text.*)", as well as a simpler "section name regexp", eg
> ".text.*", to be used. This version only supports the latter
> format.
>
> In addition H.J.'s syntax allowed for abbreviated section names to
> match. So ".t*t" would match any section starting with ".t" and
> ending with "t" and would put it into the .text section. In this
> version however the output section is selected based upon matching
> the fixed part at the start of the pattern with the output section.
> So ".t*t" would only work if the output section was called ".t".
>
> To help compensate for this, and to allow arbitrary input sections
> to be mapped to specific output sections, the output section name
> can be provided as if it were a filename. So .foo(.bar) would map
> all sections called .bar to the output section .foo, but only if the
> linker script has an output section called .foo, and only if that
> output section declaration includes a INCLUDE section-ordering-file
> statement.
>
> Perhaps an example will make things clearer. If the above linker
> script is used and the section ordering file contains:
>
> # A comment - this will be ignored.
> .text.hot .text.cold .text.warm
> .data.big
> .data(.bar)
> .text.foo*
> .ignore(.me)
>
> This is roughly equivalent to a linker script that looks like this:
>
> SECTIONS
> {
> .text : {
> *(.text.hot)
> *(.text.cold)
> *(.text.warm)
> *(.text.foo*)
> *(.text)
> }
> .data : {
> *(.data.big)
> *(.bar)
> *(.data)
> }
> }
>
> Note - the linker will not warn about entries in the section
> ordering file that do not match an output section name. So in the
> above example the ".ignore(.me)" entry will not generate a warning
> about it not being used.
>
> Thoughts, comments, etc ?
This seems really clunky to me. How about a script that augments
the default script, but looks very similar to other scripts, ie. with
a SECTIONS clause? To take your example, use a script like:
SECTIONS
{
.text : {
*(.text.hot)
*(.text.cold)
*(.text.warm)
*(.text.foo*)
}
.data : {
*(.data.big)
*(.bar)
}
}
Then arrange to insert the contents of each output section statement
in this script at the start of corresponding output section statement
in the default script.
--
Alan Modra
Australia Development Lab, IBM
next prev parent reply other threads:[~2024-04-26 4:17 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-25 13:01 Nick Clifton
2024-04-25 15:32 ` H.J. Lu
2024-04-26 9:38 ` Nick Clifton
2024-04-26 1:46 ` Hans-Peter Nilsson
2024-04-26 9:46 ` Nick Clifton
2024-04-27 0:46 ` Hans-Peter Nilsson
2024-04-26 4:17 ` Alan Modra [this message]
2024-04-26 9:59 ` Nick Clifton
2024-04-26 12:43 ` Alan Modra
2024-04-29 0:12 ` Alan Modra
2024-05-02 15:16 ` Nick Clifton
2024-05-06 18:27 ` H.J. Lu
2024-05-07 16:39 ` RFC: ld: Add --text-section-ordering-file (version 4) Nick Clifton
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