Received-SPF: pass (google.com: domain of linux-kernel+bounces-206689-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 216.228.117.160 as permitted sender) receiver=protection.outlook.com;
 client-ip=216.228.117.160; helo=mail.nvidia.com; pr=C
Message-ID: <6b32399f-d9c6-4df5-b1e5-755ef4acf25d@nvidia.com>
Date: Fri, 7 Jun 2024 13:13:23 -0700
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v2 1/2] selftests/lib.mk: handle both LLVM=1 and CC=clang
 builds
To: Nathan Chancellor <nathan@kernel.org>, Ryan Roberts <ryan.roberts@arm.com>
CC: Mark Brown <broonie@kernel.org>, Shuah Khan <shuah@kernel.org>, "Muhammad
 Usama Anjum" <usama.anjum@collabora.com>, Beau Belgrave
	<beaub@linux.microsoft.com>, Steven Rostedt <rostedt@goodmis.org>, "Naresh
 Kamboju" <naresh.kamboju@linaro.org>, Nick Desaulniers
	<ndesaulniers@google.com>, Justin Stitt <justinstitt@google.com>, "Bill
 Wendling" <morbo@google.com>, sunliming <sunliming@kylinos.cn>, "Masami
 Hiramatsu" <mhiramat@kernel.org>, Valentin Obst <kernel@valentinobst.de>,
	<linux-kselftest@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	<llvm@lists.linux.dev>
References: <20240531183751.100541-1-jhubbard@nvidia.com>
 <20240531183751.100541-2-jhubbard@nvidia.com>
 <306eebf8-bb5d-4e1a-9fa3-ad3f4ea11b9c@sirena.org.uk>
 <20240603224706.GA245774@thelio-3990X>
 <2c57be33-77b8-419b-a708-e99aa9b44395@nvidia.com>
 <0d3fd536-5036-40e7-9783-80533914e32d@arm.com>
 <20240607171533.GA2636750@thelio-3990X>
Content-Language: en-US
From: John Hubbard <jhubbard@nvidia.com>
In-Reply-To: <20240607171533.GA2636750@thelio-3990X>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Jun 2024 20:13:42.7560
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: fd7b5c24-cba7-4ee3-72b2-08dc872e5419
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource:
	CO1PEPF000044EE.namprd05.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV3PR12MB9093

On 6/7/24 10:15 AM, Nathan Chancellor wrote:
> On Fri, Jun 07, 2024 at 12:12:19PM +0100, Ryan Roberts wrote:
>> On 04/06/2024 05:55, John Hubbard wrote:
>>> On 6/3/24 3:47 PM, Nathan Chancellor wrote:
...
>> If we are concluding that CC=clang is an invalid way to do this, then I guess we
>> should report that back to [1]?
>>
>> [1] https://lore.kernel.org/all/202404141807.LgsqXPY5-lkp@intel.com/
>> [2]
>> https://lore.kernel.org/linux-kselftest/20240417160740.2019530-1-ryan.roberts@arm.com/
> 
> I can only speak from the perspective of the main kernel build, as I
> don't really know much if anything about the selftests, but I think
> CC=clang and LLVM=1 should both be valid. Ideally, they would behave as
> they do for the main kernel build (i.e., CC=clang just uses clang for
> the compiler and LLVM=1 uses the entire LLVM tools). I realize that for
> the selftests, there is probably little use for tools other than the
> compiler, assembler, and linker but I think consistency is desirable
> here.
> 
> I am not at all familiar with the selftests build system, which is
> completely different from Kbuild, but I would ack a patch that does
> that. Otherwise, I think having a different meaning or handling of
> CC=clang or LLVM=1 is the end of the world, but I do think that it
> should be documented.
> 

OK, that can be easily done, as shown below. And there are so far only
a handful of selftests that key off of LLVM (plus a few of my pending
patches). I can post this, plus a few patches (and patch updates for
pending patches) to use the new CC_IS_CLANG where appropriate:

diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
index 429535816dbd..ea643d1a65dc 100644
--- a/tools/testing/selftests/lib.mk
+++ b/tools/testing/selftests/lib.mk
@@ -43,6 +43,15 @@ else
  CC := $(CROSS_COMPILE)gcc
  endif # LLVM
  
+# CC might have been set above (by inferring it from LLVM==1), or CC might have
+# been set from the environment. In either case, if CC is an invocation of clang
+# in any form, set CC_IS_CLANG. This allows subsystem selftests to selectively
+# control clang-specific behavior, such as, in particular, compiler warnings.
+CC_IS_CLANG := 0
+ifeq ($(findstring clang,$(CC)),clang)
+    CC_IS_CLANG := 1
+endif
+
  ifeq (0,$(MAKELEVEL))
      ifeq ($(OUTPUT),)
         OUTPUT := $(shell pwd)


thanks,
-- 
John Hubbard
NVIDIA