linux-kernel - Re: [PATCH 1/2] selftests/openat2: fix clang build failures: -static-libasan, LOCAL

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Message-ID: <518dd1e3-e31a-41c3-b488-9b75a64b6c8a@arm.com>
Date: Tue, 7 May 2024 17:34:14 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: John Hubbard <jhubbard@...dia.com>, Shuah Khan <shuah@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
 Christian Brauner <brauner@...nel.org>,
 Muhammad Usama Anjum <usama.anjum@...labora.com>,
 Alexey Gladkov <legion@...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 1/2] selftests/openat2: fix clang build failures:
 -static-libasan, LOCAL_HDRS

On 07/05/2024 17:19, John Hubbard wrote:
> On 5/7/24 12:45 AM, Ryan Roberts wrote:
>> On 04/05/2024 05:43, John Hubbard wrote:
> ...
>> Hi John,
>>
>> I sent out a similar fix a couple of weeks ago, see [1]. I don't think it got
>> picked up though. It takes a slightly different approach, explicitly adding
>> -static-libsan (note no 'a') for clang, instead of relying on its default.
>>
>> And it just drops helpers.h from the makefile altogether, on the assumption that
>> it was a mistake; its just a header and shouldn't be compiled directly. I'm not
>> exactly sure what the benefit of adding it to LOCAL_HDRS is?
> 
> Ah no, you must not drop headers.h. That's a mistake itself, because
> LOCAL_HDRS adds a Make dependency; that's its purpose. If you touch
> helpers.h it should cause a rebuild, which won't happen if you remove it
> from LOCAL_HDRS.

Ahh. I was under the impression that the compiler was configured to output the
list of dependencies for make to track (something like -M, from memory ?). Since
helpers.h is included from helpers.c I assumed it would be tracked like this - I
guess its not that simple?

Anyway, on the basis that LOCAL_HDRS is the right way to do this, let's go with
your version and drop mine:

Reviewed-by: Ryan Roberts <ryan.roberts@....com>

> 
> The way it works is that lib.mk adds $(LOCAL_HDRS) to the dependencies list,
> but then filters precisely that same set *out* of the list that it provides
> to the compile invocation.
> 
> The other way to implement this requirement of "some things need to be
> Make dependencies, and some need to be both dependencies and compilation
> inputs", is to add everything to the dependency list, but then use a
> separate list of files to pass to the compiler. For an example of that,
> see $(EXTRA_FILES) in patch 1/7 [1] of my selftests/x86 cleanup.
> 
> [1] https://lore.kernel.org/all/20240503030214.86681-2-jhubbard@nvidia.com/
> 
> thanks,
> John Hubbard
> 
>>
>> [1]
>> https://lore.kernel.org/linux-kselftest/20240417160740.2019530-1-ryan.roberts@arm.com/
>>
>> Thanks,
>> Ryan
>>
>>
>>> ---
>>>   tools/testing/selftests/openat2/Makefile | 14 ++++++++++++--
>>>   1 file changed, 12 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/testing/selftests/openat2/Makefile
>>> b/tools/testing/selftests/openat2/Makefile
>>> index 254d676a2689..185dc76ebb5f 100644
>>> --- a/tools/testing/selftests/openat2/Makefile
>>> +++ b/tools/testing/selftests/openat2/Makefile
>>> @@ -1,8 +1,18 @@
>>>   # SPDX-License-Identifier: GPL-2.0-or-later
>>>   -CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined
>>> -static-libasan
>>> +CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined
>>>   TEST_GEN_PROGS := openat2_test resolve_test rename_attack_test
>>>   +# gcc requires -static-libasan in order to ensure that Address Sanitizer's
>>> +# library is the first one loaded. However, clang already statically links the
>>> +# Address Sanitizer if -fsanitize is specified. Therefore, simply omit
>>> +# -static-libasan for clang builds.
>>> +ifeq ($(LLVM),)
>>> +    CFLAGS += -static-libasan
>>> +endif
>>> +
>>> +LOCAL_HDRS += helpers.h
>>> +
>>>   include ../lib.mk
>>>   -$(TEST_GEN_PROGS): helpers.c helpers.h
>>> +$(TEST_GEN_PROGS): helpers.c
>>>
>>> base-commit: ddb4c3f25b7b95df3d6932db0b379d768a6ebdf7
>>> prerequisite-patch-id: b901ece2a5b78503e2fb5480f20e304d36a0ea27
>>
> 
> thanks,