linux-kernel - Re: [PATCH] kbuild: clang: remove crufty HOSTCFLAGS

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Date:   Fri, 6 Oct 2017 05:15:50 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Nick Desaulniers <nick.desaulniers@...il.com>
Cc:     Behan Webster <behanw@...verseincode.com>, dl9pf@....de,
        Mark Charlebois <charlebm@...il.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Michael Davidson <md@...gle.com>,
        Michal Marek <mmarek@...e.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvmlinux@...ts.linuxfoundation.org
Subject: Re: [PATCH] kbuild: clang: remove crufty HOSTCFLAGS

Hi Nick.

2017-10-01 8:14 GMT+09:00 Nick Desaulniers <nick.desaulniers@...il.com>:
> On Thu, Sep 28, 2017 at 07:52:35PM +0900, Masahiro Yamada wrote:
>> 2017-09-26 11:28 GMT+09:00 Nick Desaulniers <nick.desaulniers@...il.com>:
>> >  HOSTCFLAGS   := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \
>> > +               $(call hostcc-option,-fno-delete-null-pointer-checks) \
>> >                 -fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS)
>>
>> You call hostcc-option
>> before Kbuild.include is included around line 341.
>>
>> So, $(call hostcc-option, ...) returns always an empty string here
>> whether the compiler supports the option or not.
>
> So calling a yet-to-be defined variable results in an empty string
> rather than a loud failure?  Chalk that up there with language features
> no one ever asked for.  That kind of implicit conversion gets languages
> like JavaScript (with its loose type system, not that C is without its
> own implicit type conversions/promotions) in a lot of hot water.
>
> If that's the case, why are includes not at the top of Makefiles, if
> silent failure is a possibility?  Is there a reason the include is so
> far into the Makefile?

Kbuild.include depends on some other variables.
You can not include it at the top of the Makefile.



> Is your sugguestion to raise the include or lower the HOSTCFLAGS
> definition?


In this case, you do not need to move any of them.

-fno-delete-null-pointer-checks has never enabled
for host-tools before.

Just remove it to keep the current behavior.


>> > -ifeq ($(shell $(HOSTCC) -v 2>&1 | grep -c "clang version"), 1)
>> > -HOSTCFLAGS  += -Wno-unused-value -Wno-unused-parameter \
>> > -               -Wno-missing-field-initializers -fno-delete-null-pointer-checks
>> > -endif
>>
>> The logic is very strange in the first place.
>>
>> Even very old GCC supports -fno-delete-null-pointer-checks,
>> but clang does not.
>>
>> Here, -fno-delete-null-pointer-checks is added only when
>> we are using clang for HOSTCC.  This is opposite.
>>
>> I guess we can remove all of them
>> unless somebody can explain the rationale.
>
> +llvm-linux
>
> I suppose maybe different ARCH's have different host binaries made
> during the build?  I tested x86_64 and arm64.  The commit message that
> added them missed any context or justification.


According to
http://llvm.linuxfoundation.org/index.php/Main_Page

llvm-linux was only successful for x86, arm(64)
at that time.

If you tested x86_64 and arm64, and saw no problem,
it is fine.





-- 
Best Regards
Masahiro Yamada