linux-kernel - Re: [PATCH v2 2/2] kbuild: lto: preserve MAKEFLAGS for module linking

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Date:   Tue, 20 Sep 2022 10:06:46 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Martin Liska <mliska@...e.cz>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2 2/2] kbuild: lto: preserve MAKEFLAGS for module linking

On 19. 07. 22, 11:15, Masahiro Yamada wrote:
> On Tue, Jul 19, 2022 at 5:41 PM Jiri Slaby <jslaby@...e.cz> wrote:
>>
>> From: Martin Liska <mliska@...e.cz>
>>
>> Prefix command in makefile run in order to preserve access to jobserver.
>> This is needed for gcc at least.
>>
>> Fixes this warning:
>> lto-wrapper: warning: jobserver is not available: ‘--jobserver-auth=’ is not present in ‘MAKEFLAGS’
> 
> 
> What is lto-wrapper ?

lto-wrapper is a part of gcc:
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/lto-wrapper.cc

And is invoked during the link of LTO objects (also to link in parallel 
if jobserver is available).

I am leaving the unanswered questions below for Martin to answer.

>> Cc: Sedat Dilek <sedat.dilek@...il.com>
>> Cc: Masahiro Yamada <masahiroy@...nel.org>
>> Cc: Michal Marek <michal.lkml@...kovi.net>
>> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
>> Fixes: 5d45950dfbb1 (kbuild: move vmlinux.o link to scripts/Makefile.vmlinux_o)
>> Signed-off-by: Martin Liska <mliska@...e.cz>
>> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
>> ---
>>
>> Notes:
>>      [v2] this is new in v2
>>
>>   scripts/Makefile.build | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
>> index bb63374fb055..493f3c4e8461 100644
>> --- a/scripts/Makefile.build
>> +++ b/scripts/Makefile.build
>> @@ -247,8 +247,8 @@ endef
>>
>>   # Built-in and composite module parts
>>   $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
>> -       $(call if_changed_rule,cc_o_c)
>> -       $(call cmd,force_checksrc)
>> +       +$(call if_changed_rule,cc_o_c)
>> +       +$(call cmd,force_checksrc)
> 
> 
> cmd_force_checksrc invokes sparse.
> How is it related to GCC?
> 
> 
> 
> 
>>
>>   # To make this rule robust against "Argument list too long" error,
>>   # ensure to add $(obj)/ prefix by a shell command.
>> @@ -457,7 +457,7 @@ endef
>>   $(multi-obj-m): objtool-enabled := $(delay-objtool)
>>   $(multi-obj-m): part-of-module := y
>>   $(multi-obj-m): %.o: %.mod FORCE
>> -       $(call if_changed_rule,ld_multi_m)
>> +       +$(call if_changed_rule,ld_multi_m)
>>   $(call multi_depend, $(multi-obj-m), .o, -objs -y -m)
> 
> 
> cmd_ld_multi_m invokes $(LD) directly.
> How is it related to gcc?



-- 
js
suse labs