hot/cold section support

[Doug Evans]

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).