linux-kernel - Re: [PATCH] tools/lib/api: allow the linker to be overridden

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Date:   Wed, 15 Feb 2017 16:25:17 +0100
From:   Marcin Nowakowski <marcin.nowakowski@...tec.com>
To:     Arnaldo Carvalho de Melo <acme@...hat.com>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tools/lib/api: allow the linker to be overridden

Hi Arnaldo,

On 15.02.2017 16:18, Arnaldo Carvalho de Melo wrote:
> Em Wed, Feb 15, 2017 at 03:56:30PM +0100, Marcin Nowakowski escreveu:
>> Makefile in lib/api unconditionally sets the LD to support
>> cross-compilation. However, when invoked from within the perf build LD
>> may be already appropriately set for a given platform and the override
>> may lead to cross-compilation without appropriate linker flags.
>
>> Change the unconditional override to a conditional one.
>>
>> Fixes: 37b4e2020a5f ('perf build: Add EXTRA_LDFLAGS option to makefile')
>> Fixes: 703e01652d25 ('tools lib api: Respect CROSS_COMPILE for the linker')
>>
>> Signed-off-by: Marcin Nowakowski <marcin.nowakowski@...tec.com>
>> ---
>>  tools/lib/api/Makefile | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/lib/api/Makefile b/tools/lib/api/Makefile
>> index adba83b..42e00c4 100644
>> --- a/tools/lib/api/Makefile
>> +++ b/tools/lib/api/Makefile
>> @@ -10,7 +10,7 @@ endif
>>
>>  CC = $(CROSS_COMPILE)gcc
>>  AR = $(CROSS_COMPILE)ar
>> -LD = $(CROSS_COMPILE)ld
>> +LD ?= $(CROSS_COMPILE)ld
>
> Looks strange to do this just for LD, what about CC and AR?
>
> - Arnaldo

I agree it looks a bit strange and at first I was thinking about doing 
that, but the problem is that for eg. CC that doesn't work, because make 
internally defines CC.
Perf uses a workaround for this:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/tools/perf/Makefile.perf#n136

so if you want I could move that to lib/api as well.

On the other hand the main problem that exists here is that for CC, all 
extra variables are handled by EXTRA_CFLAGS variable that is used by 
various makefiles, while there is no such 'global' equivalent for 
LDFLAGS that could be used and this was 'merged' into the LD in commit 
37b4e2020a5f (and later broken again by 703e01652d25).

Marcin