Source Code for Profile Guided Code Positioning

[Maxim Ostapenko]

On 20/01/16 10:08, Sriraman Tallam wrote:
> On Fri, Jan 15, 2016 at 9:51 AM, Yury Gribov <y.gribov@samsung.com> wrote:
>> On 01/15/2016 08:44 PM, vivek pandya wrote:
>>> Thanks Yury for
>>> https://gcc.gnu.org/ml/gcc-patches/2011-09/msg01440.html this link.
>>> It implements procedure reordering as linker plugin.
>>> I have some questions :
>>> 1 ) Can you point me to some documentation for "how to write plugin
>>> for linkers " I am I have not seen doc for structs with 'ld_' prefix
>>> (i.e defined in plugin-api.h )
>>>    2 ) There is one more algorithm for Basic Block ordering with
>>> execution frequency count in PH paper . Is there any implementation
>>> available for it ?
>>
>> Quite frankly - I don't know (I've only learned about Google implementation
>> recently).
>>
>> I've added Sriram to maybe comment.
> Sorry for the late response.  The google/gcc_4_9 branch has the source
> of function reordering linker Plugin.  It is available in the
> function_reordering_plugin directory under the top level gcc
> directory.
>
> The function reordering plugin constructs a callgraph and uses profile
> information to do a Pettis Hansen style function reordering.   This
> plugin does not do basic block re-ordering.
>
> There is no documentation as such that I am aware of to write a linker
> plugin.  Here is a very brief overview.   The linker calls the
> plugin's "onload" function when registering the plugin and the plugin
> inturn can register two call-backs with the linker, "claim_file_hook"
> and the "all_symbols_read_hook".  "claim_file_hook" is called  for
> each object file that the linker prcesses and the
> "all_symbols_read_hook" is called after all the symbols have been read
> by the linker.  These are just two different interesting points in the
> course of a link.
>
> The plugin can also get handles to linker functions like
> "get_input_section_name" which it can use to process sections given
> their handle. You can also check the gold linker tests for simpler
> plugin examples.
>
> HTH,
> Thanks
> Sri

Very interesting, thank you! Actually, I see -freorder-functions switch 
in GCC that allows perform pretty the same optimizations in linker, 
right? Just wondering if you achieved to get performance improvements 
against -freorder-functions with your plugin.

Thanks,
-Maxim

>> -Y
>