linux-kernel - Re: [PATCH] selftests/binderfs: use the Makefile's rules, not Make's implicit rules

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Date: Fri, 3 May 2024 11:10:38 +0200
From: Christian Brauner <brauner@...nel.org>
To: John Hubbard <jhubbard@...dia.com>
Cc: Shuah Khan <shuah@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Kees Cook <keescook@...omium.org>, Valentin Obst <kernel@...entinobst.de>, 
	linux-kselftest@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH] selftests/binderfs: use the Makefile's rules, not Make's
 implicit rules

On Thu, May 02, 2024 at 06:58:20PM -0700, John Hubbard wrote:
> First of all, in order to build with clang at all, one must first apply
> Valentin Obst's build fix for LLVM [1]. Once that is done, then when
> building with clang, via:
> 
>     make LLVM=1 -C tools/testing/selftests
> 
> ...the following error occurs:
> 
>    clang: error: cannot specify -o when generating multiple output files
> 
> This is because clang, unlike gcc, won't accept invocations of this
> form:
> 
>     clang file1.c header2.h
> 
> While trying to fix this, I noticed that:
> 
> a) selftests/lib.mk already avoids the problem, and
> 
> b) The binderfs Makefile indavertently bypasses the selftests/lib.mk
> build system, and quitely uses Make's implicit build rules for .c files
> instead.
> 
> The Makefile attempts to set up both a dependency and a source file,
> neither of which was needed, because lib.mk is able to automatically
> handle both. This line:
> 
>     binderfs_test: binderfs_test.c
> 
> ...causes Make's implicit rules to run, which builds binderfs_test
> without ever looking at lib.mk.
> 
> Fix this by simply deleting the "binderfs_test:" Makefile target and
> letting lib.mk handle it instead.
> 
> [1] https://lore.kernel.org/all/20240329-selftests-libmk-llvm-rfc-v1-1-2f9ed7d1c49f@valentinobst.de/
> 
> Fixes: 6e29225af902 ("binderfs: port tests to test harness infrastructure")
> Cc: Christian Brauner <brauner@...nel.org>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---

Reviewed-by: Christian Brauner <brauner@...nel.org>