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

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Message-ID: <20240503015820.76394-1-jhubbard@nvidia.com>
Date: Thu,  2 May 2024 18:58:20 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Shuah Khan <shuah@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	John Hubbard <jhubbard@...dia.com>,
	Christian Brauner <brauner@...nel.org>,
	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: [PATCH] selftests/binderfs: use the Makefile's rules, not Make's implicit rules

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>
---
 tools/testing/selftests/filesystems/binderfs/Makefile | 2 --
 1 file changed, 2 deletions(-)

diff --git a/tools/testing/selftests/filesystems/binderfs/Makefile b/tools/testing/selftests/filesystems/binderfs/Makefile
index c2f7cef919c0..eb4c3b411934 100644
--- a/tools/testing/selftests/filesystems/binderfs/Makefile
+++ b/tools/testing/selftests/filesystems/binderfs/Makefile
@@ -3,6 +3,4 @@
 CFLAGS += $(KHDR_INCLUDES) -pthread
 TEST_GEN_PROGS := binderfs_test
 
-binderfs_test: binderfs_test.c ../../kselftest.h ../../kselftest_harness.h
-
 include ../../lib.mk

base-commit: f03359bca01bf4372cf2c118cd9a987a5951b1c8
prerequisite-patch-id: b901ece2a5b78503e2fb5480f20e304d36a0ea27
-- 
2.45.0