linux-kernel - Re: [PATCH for 5.2 12/12] rseq/selftests: add -no-integrated-as for clang

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Date:   Mon, 29 Apr 2019 16:28:18 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     ndesaulniers <ndesaulniers@...gle.com>, shuah <shuah@...nel.org>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
        Chris Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
        rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        linux-kselftest <linux-kselftest@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH for 5.2 12/12] rseq/selftests: add -no-integrated-as for
 clang

----- On Apr 29, 2019, at 1:03 PM, ndesaulniers ndesaulniers@...gle.com wrote:

> On Mon, Apr 29, 2019 at 8:29 AM Mathieu Desnoyers
> <mathieu.desnoyers@...icios.com> wrote:
>>
>> Ongoing work for asm goto support from clang requires the
>> -no-integrated-as compiler flag.
>>
>> This compiler flag is present in the toplevel kernel Makefile,
>> but is not replicated for selftests. Add it specifically for
>> the rseq selftest which requires asm goto.
>>
>> Link: https://reviews.llvm.org/D56571
>> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> CC: Nick Desaulniers <ndesaulniers@...gle.com>
>> CC: Thomas Gleixner <tglx@...utronix.de>
>> CC: Joel Fernandes <joelaf@...gle.com>
>> CC: Peter Zijlstra <peterz@...radead.org>
>> CC: Catalin Marinas <catalin.marinas@....com>
>> CC: Dave Watson <davejwatson@...com>
>> CC: Will Deacon <will.deacon@....com>
>> CC: Shuah Khan <shuah@...nel.org>
>> CC: Andi Kleen <andi@...stfloor.org>
>> CC: linux-kselftest@...r.kernel.org
>> CC: "H . Peter Anvin" <hpa@...or.com>
>> CC: Chris Lameter <cl@...ux.com>
>> CC: Russell King <linux@....linux.org.uk>
>> CC: Michael Kerrisk <mtk.manpages@...il.com>
>> CC: "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
>> CC: Paul Turner <pjt@...gle.com>
>> CC: Boqun Feng <boqun.feng@...il.com>
>> CC: Josh Triplett <josh@...htriplett.org>
>> CC: Steven Rostedt <rostedt@...dmis.org>
>> CC: Ben Maurer <bmaurer@...com>
>> CC: linux-api@...r.kernel.org
>> CC: Andy Lutomirski <luto@...capital.net>
>> CC: Andrew Morton <akpm@...ux-foundation.org>
>> CC: Linus Torvalds <torvalds@...ux-foundation.org>
>> ---
>>  tools/testing/selftests/rseq/Makefile | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/rseq/Makefile
>> b/tools/testing/selftests/rseq/Makefile
>> index c30c52e1d0d2..d6469535630a 100644
>> --- a/tools/testing/selftests/rseq/Makefile
>> +++ b/tools/testing/selftests/rseq/Makefile
>> @@ -1,5 +1,11 @@
>>  # SPDX-License-Identifier: GPL-2.0+ OR MIT
>> -CFLAGS += -O2 -Wall -g -I./ -I../../../../usr/include/ -L./ -Wl,-rpath=./
>> +
>> +ifneq ($(shell $(CC) --version 2>&1 | head -n 1 | grep clang),)
>> +CLANG_FLAGS += -no-integrated-as
>> +endif
>> +
>> +CFLAGS += -O2 -Wall -g -I./ -I../../../../usr/include/ -L./ -Wl,-rpath=./ \
>> +         $(CLANG_FLAGS)
> 
> The top level Makefile exports $(CLANG_FLAGS), which should contain
> `-no-integrated-as`.  Is that available here?  If so, then you can
> just add `$(CLANG_FLAGS)`, no compiler check needed.

AFAIU, the makefiles under tools/testing/selftests all end up including
tools/testing/selftests/lib.mk, which states:

"# This mimics the top-level Makefile. We do it explicitly here so that this
 # Makefile can operate with or without the kbuild infrastructure."

So I don't think it's using any of the definitions from the toplevel
Makefile.

> If not, maybe the test for CONFIG_CC_IS_CLANG is cleaner?

A quick test indicates that the toplevel CONFIG_* definitions are unavailable
from the kernel selftests makefiles.

> Thanks for the patch, and helping test asm goto in Clang!

You're very welcome! Considering that I intend to have rseq widely adopted in
user-space, it's only natural to consider that its user-space side needs to be
compiled by clang as well.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com