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

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Date:   Sat, 30 Sep 2017 19:38:53 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Nick Desaulniers <nick.desaulniers@...il.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        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

On Sat, Sep 30, 2017 at 04:14:50PM -0700, Nick Desaulniers wrote:
> 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.

make --warn-undefined-variables

(and it warns all over the place during a kernel build -- having undefined
variables expand to the empty string is a useful feature, too, not just a
trap for the unwary).


Segher