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Subject: Re: [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang
To:     Nick Desaulniers <ndesaulniers@google.com>, namit@vmware.com
Cc:     Nathan Chancellor <natechancellor@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, mingo@redhat.com,
        bp@alien8.de, x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>
References: <20181023003725.21463-1-natechancellor@gmail.com>
 <F3BBC06A-A9CB-4ABF-ADF4-6B0971FAE364@vmware.com>
 <CAKwvOdmsKbW9v9or+u-W9V7T+LrF4ODY9cgUStkjkmsbMcqJ2g@mail.gmail.com>
From:   "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <96ffedd2-a19d-95de-45fd-3a83025dd48a@zytor.com>
Date:   Tue, 23 Oct 2018 13:01:22 -0700
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On 10/23/18 11:40, Nick Desaulniers wrote:
> On Mon, Oct 22, 2018 at 10:11 PM Nadav Amit <namit@vmware.com> wrote:
>>
>> at 5:37 PM, Nathan Chancellor <natechancellor@gmail.com> wrote:
>>
>> Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in
>> inline assembly code to work around asm() related GCC inlining bugs")
>> added this flag to KBUILD_CFLAGS, where it works perfectly fine with
>> GCC. However, when building with Clang, all of the object files compile
>> fine but the build hangs indefinitely at init/main.o, right before the
>> linking stage. Don't include this flag when building with Clang.
>>
>> The kernel builds and boots to a shell in QEMU with both GCC and Clang
>> with this patch applied.
>>
>> Link: https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&amp;data=02%7C01%7Cnamit%40vmware.com%7C871daebc2ca44947d28d08d638811fb5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636758524579997650&amp;sdata=shuxW81QRrO3TSqbgf462wgZYdLeAKeQEdGRxmnUX30%3D&amp;reserved=0
>> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
>> ---
>>
>> The reason this patch is labeled RFC is while I can verify that this
>> fixes the issue, I'm not entirely sure why the '-Wa,-' works for GCC
>> and not Clang. I looked into what the flag means and I couldn't really
>> find anything so I just assume it's taking input from stdin? The issue
>> could stem from how GCC forks gas versus how Clang does it. If this
>> isn't of concern and the maintainers are happy with this patch as is,
>> feel free to take it.
>>

Perhaps someone could actually, you know, time the build and see how
much -pipe actually matters, if at all?

	-hpa