Re: Aligning function on a page boundary

["Igor Bukanov" <igor at mir2 dot org>]

Hi Sam,

I have tried to use __attribute__((section("xxx")), but it seems there
are no linker options to force a particular alignment for a section
for ELF. All those nice alignment options refers to Windows:

--section-alignment
           Sets  the  section alignment.  Sections in memory will
always begin at addresses which are a multiple of this number.
Defaults to 0x1000.  [This option is specific to the i386 PE targeted
port of the linker]

I can only force the section to start on a particular address when
loaded. Then it works. But this is not what as I have no idea what the
address should be.

Have I missed something?

Regards, Igor

On 27/02/2008, Sam Ravnborg <sam@ravnborg.org> wrote:
> On Wed, Feb 27, 2008 at 01:51:10PM +0100, Igor Bukanov wrote:
>  > Hi,
>  >
>  > is it possible with GCC 4.1 to align one single function on a CPU page
>  > boundary for ELF targets? This is very desired since the function in
>  > question is an interpreter loop . It has 50K of code and is executed
>  > very often. Aligning it on the page boundary should reduce TLB misses.
>  >
>  > It seems the forthcoming GCC 4.3 allows that as it supports the align
>  > attribute for functions,  but it would be nice to do that with GCC
>  > 4.1.
>
>
> One way is to use the section attribute to tell gcc to put the
>  function in a specific section and then in the linker script
>  page align said section.
>  This is used extensively in the linux kernel.
>
>
>         Sam
>