linux-kernel - [PATCH v2 4/6] selftests/x86: avoid -no-pie warnings from clang during compilation

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Date: Mon, 27 May 2024 14:00:40 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Shuah Khan <shuah@...nel.org>
Cc: angquan yu <angquan21@...il.com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>,
	Binbin Wu <binbin.wu@...ux.intel.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Sohil Mehta <sohil.mehta@...el.com>,
	Yu-cheng Yu <yu-cheng.yu@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Valentin Obst <kernel@...entinobst.de>,
	linux-kselftest@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	llvm@...ts.linux.dev,
	x86@...nel.org,
	John Hubbard <jhubbard@...dia.com>
Subject: [PATCH v2 4/6] selftests/x86: avoid -no-pie warnings from clang during compilation

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

..clang warns that -no-pie is "unused during compilation".

This occurs because clang only wants to see -no-pie during linking.
Here, we don't have a separate linking stage, so a compiler warning is
unavoidable without (wastefully) restructuring the Makefile.

Avoid the warning by simply disabling that warning, for clang builds.

[1] https://lore.kernel.org/all/20240329-selftests-libmk-llvm-rfc-v1-1-2f9ed7d1c49f@valentinobst.de/

Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 tools/testing/selftests/x86/Makefile | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index d0bb32bd5538..5c8757a25998 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -40,6 +40,13 @@ CFLAGS := -O2 -g -std=gnu99 -pthread -Wall $(KHDR_INCLUDES)
 # call32_from_64 in thunks.S uses absolute addresses.
 ifeq ($(CAN_BUILD_WITH_NOPIE),1)
 CFLAGS += -no-pie
+
+ifneq ($(LLVM),)
+# clang only wants to see -no-pie during linking. Here, we don't have a separate
+# linking stage, so a compiler warning is unavoidable without (wastefully)
+# restructuring the Makefile. Avoid this by simply disabling that warning.
+CFLAGS += -Wno-unused-command-line-argument
+endif
 endif
 
 define gen-target-rule-32
-- 
2.45.1