Re: [PATCH v3 2/8] lib: collect library files in an archive

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Jan,

> On 9 Dec 2020, at 14:42, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> 
> On 09.12.2020 12:37, Bertrand Marquis wrote:
>>> On 23 Nov 2020, at 15:21, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>> 
>>> In order to (subsequently) drop odd things like CONFIG_NEEDS_LIST_SORT
>>> just to avoid bloating binaries when only some arch-es and/or
>>> configurations need generic library routines, combine objects under lib/
>>> into an archive, which the linker then can pick the necessary objects
>>> out of.
>>> 
>>> Note that we can't use thin archives just yet, until we've raised the
>>> minimum required binutils version suitably.
>>> 
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> 
> Thanks.
> 
>>> @@ -60,7 +64,14 @@ include Makefile
>>> # 
>>> ---------------------------------------------------------------------------
>>> 
>>> quiet_cmd_ld = LD      $@
>>> -cmd_ld = $(LD) $(XEN_LDFLAGS) -r -o $@ $(real-prereqs)
>>> +cmd_ld = $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter-out %.a,$(real-prereqs)) \
>>> +               --start-group $(filter %.a,$(real-prereqs)) --end-group
>> 
>> This might be a good idea to add a comment to explain why the start/end-group
>> is needed so that someone does not change this back in the future.
> 
> Since we're trying to inherit Linux'es build system, I did look
> there and iirc there was no comment, so I didn't see a basis for
> us to have one.
> 
>> Something like: put libraries between start/end group to have unused symbols 
>> removed.
> 
> Now that's not the reason - why you describe is the default
> behavior for archives, and there is something like a "whole
> archive" option iirc to change to a mode where all objects
> get pulled out. Instead this is a symbol resolution thing
> aiui - by default earlier archives can't resolve undefined
> symbols first referenced by objects pulled out of later
> archives.

ah yes i remember seeing that.
Maybe just add your last sentence in the commit message.

Cheers
Bertrand

> 
> Jan