linux-kernel - Re: [PATCH v2 1/2] selftests/lib.mk: handle both LLVM=1 and CC=clang builds

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Date: Fri, 7 Jun 2024 13:13:23 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Nathan Chancellor <nathan@...nel.org>, Ryan Roberts <ryan.roberts@....com>
CC: Mark Brown <broonie@...nel.org>, Shuah Khan <shuah@...nel.org>, "Muhammad
 Usama Anjum" <usama.anjum@...labora.com>, Beau Belgrave
	<beaub@...ux.microsoft.com>, Steven Rostedt <rostedt@...dmis.org>, "Naresh
 Kamboju" <naresh.kamboju@...aro.org>, Nick Desaulniers
	<ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, "Bill
 Wendling" <morbo@...gle.com>, sunliming <sunliming@...inos.cn>, "Masami
 Hiramatsu" <mhiramat@...nel.org>, Valentin Obst <kernel@...entinobst.de>,
	<linux-kselftest@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
	<llvm@...ts.linux.dev>
Subject: Re: [PATCH v2 1/2] selftests/lib.mk: handle both LLVM=1 and CC=clang
 builds

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