Date: Tue, 20 Jun 2017 10:37:21 -0700
From: Matthias Kaehlcke <mka@chromium.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: hpa@zytor.com, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H . J . Lu" <hjl.tools@gmail.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Michal Marek <mmarek@suse.com>, x86@kernel.org,
        linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
        Michael Davidson <md@google.com>, Greg Hackmann <ghackmann@google.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Stephen Hines <srhines@google.com>, Kees Cook <keescook@chromium.org>,
        Arnd Bergmann <arnd@arndb.de>, Bernhard.Rosenkranzer@linaro.org,
        Peter Foley <pefoley2@pefoley.com>,
        Behan Webster <behanw@converseincode.com>,
        Douglas Anderson <dianders@chromium.org>
Subject: Re: [PATCH v4 3/3] x86/build: Specify stack alignment for clang
Message-ID: <20170620173721.GA52338@google.com>
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 <20170619204704.GP141096@google.com>
 <20170620092054.7d2mgzx6cw3jvgji@gmail.com>
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El Tue, Jun 20, 2017 at 11:20:54AM +0200 Ingo Molnar ha dit:

> 
> * Matthias Kaehlcke <mka@chromium.org> wrote:
> 
> > Ingo didn't like the duplication and suggested the use of a variable, which 
> > kinda implies a check for the compiler name.
> 
> I don't think it implies that: why cannot cc_stack_align_opt probe for the 
> compiler option and use whichever is available, without hard-coding the compiler 
> name?

We could do this:

ifneq ($(call __cc-option, $(CC), -mno-sse, -mpreferred-stack-boundary=3,),)
        cc_stack_align_opt := -mpreferred-stack-boundary
endif
ifneq ($(call cc-option, -mstack-alignment=3,),)
        cc_stack_align_opt := -mstack-alignment
endif

If preferred cc-option could be used to probe for
-mpreferred-stack-boundary , however it would require REALMODE_CFLAGS
to be moved further down in the Makefile.

Since this solution also won't win a beauty price please let me know
if it is acceptable before respinning the patch or if you have other
suggestions.

> > I also think this is a cleaner solution. [...]
> 
> I concur with hpa: hard-coding compiler is awfully fragile and ugly as well.
> 
> With the proper probing of compiler options it will be possible for compilers to 
> consolidate their options, and it would be possible for a third compiler to use a 
> mixture of GCC and Clang options. With hard-coding none of that flexibility is 
> available.
> 
> > but I'm happy to respin the patch if you have another suggestion that is ok for 
> > both of you.
> 
> Please do.
> 
> Thanks,
> 
> 	Ingo