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Re: hot/cold section support


On Thu, Sep 3, 2009 at 11:36 PM, Alan Modra<amodra@bigpond.net.au> wrote:
> This causes ld to group cold text sections together for better cache
> locality. ?I chose to put them before other text sections because this
> places the cold sections next to .init and a number of targets
> generate stubs placed at the end of .text. ?Also, placing cold
> sections at the end of .text would require non-trivial changes to
> section name matching. ?(You'd need to be able to say "match .text.*
> but not .text.*_unlikely".)
>
> I'll leave updating other ELF scripts to their respective maintainers.
>
> ? ? ? ?* scripttempl/elf.sc (.text): Add cold text sections.
>
> Index: ld/scripttempl/elf.sc
> ===================================================================
> RCS file: /cvs/src/src/ld/scripttempl/elf.sc,v
> retrieving revision 1.94
> diff -u -p -r1.94 elf.sc
> --- ld/scripttempl/elf.sc ? ? ? 1 Sep 2009 02:54:10 -0000 ? ? ? 1.94
> +++ ld/scripttempl/elf.sc ? ? ? 3 Sep 2009 15:28:06 -0000
> @@ -410,6 +410,7 @@ cat <<EOF
> ? .text ? ? ? ? ${RELOCATING-0} :
> ? {
> ? ? ${RELOCATING+${TEXT_START_SYMBOLS}}
> + ? ?${RELOCATING+*(.text.unlikely .text.*_unlikely)}
> ? ? *(.text .stub${RELOCATING+ .text.* .gnu.linkonce.t.*})
> ? ? /* .gnu.warning sections are handled specially by elf32.em. ?*/
> ? ? *(.gnu.warning)

OOC, how about a similar thing for hot sections?

I'm also curious who generates .text.*_unlikely.

P.S. There is an issue that gcc -ffunction-sections and
__attribute__((hot/cold)) don't play nice together.  Having gcc emit
hot/cold to .text.{hot,unlikely}.<label> would fix that (along with
these linker changes).


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