linux-kernel - [PATCH] kselftest/arm64: bti: force static linking

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Message-Id: <20220511172129.2078337-1-andre.przywara@arm.com>
Date:   Wed, 11 May 2022 18:21:29 +0100
From:   Andre Przywara <andre.przywara@....com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Shuah Khan <shuah@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Mark Brown <broonie@...nel.org>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] kselftest/arm64: bti: force static linking

The "bti" selftests are built with -nostdlib, which apparently
automatically creates a statically linked binary, which is what we want
and need for BTI (to avoid interactions with the dynamic linker).

However this is not true when building a PIE binary, which some
toolchains (Ubuntu) configure as the default.
When compiling btitest with such a toolchain, it will create a
dynamically linked binary, which will probably fail some tests, as the
dynamic linker might not support BTI:
===================
TAP version 13
1..18
not ok 1 nohint_func/call_using_br_x0
not ok 2 nohint_func/call_using_br_x16
not ok 3 nohint_func/call_using_blr
....
===================

To make sure we create static binaries, add an explicit -static on the
linker command line. This forces static linking even if the toolchain
defaults to PIE builds, and fixes btitest runs on BTI enabled machines.

Signed-off-by: Andre Przywara <andre.przywara@....com>
---
 tools/testing/selftests/arm64/bti/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/arm64/bti/Makefile b/tools/testing/selftests/arm64/bti/Makefile
index 73e013c082a65..dafa1c2aa5c47 100644
--- a/tools/testing/selftests/arm64/bti/Makefile
+++ b/tools/testing/selftests/arm64/bti/Makefile
@@ -39,7 +39,7 @@ BTI_OBJS =                                      \
 	teststubs-bti.o                         \
 	trampoline-bti.o
 gen/btitest: $(BTI_OBJS)
-	$(CC) $(CFLAGS_BTI) $(CFLAGS_COMMON) -nostdlib -o $@ $^
+	$(CC) $(CFLAGS_BTI) $(CFLAGS_COMMON) -nostdlib -static -o $@ $^

 NOBTI_OBJS =                                    \
 	test-nobti.o                         \
@@ -50,7 +50,7 @@ NOBTI_OBJS =                                    \
 	teststubs-nobti.o                       \
 	trampoline-nobti.o
 gen/nobtitest: $(NOBTI_OBJS)
-	$(CC) $(CFLAGS_BTI) $(CFLAGS_COMMON) -nostdlib -o $@ $^
+	$(CC) $(CFLAGS_BTI) $(CFLAGS_COMMON) -nostdlib -static -o $@ $^

 # Including KSFT lib.mk here will also mangle the TEST_GEN_PROGS list
 # to account for any OUTPUT target-dirs optionally provided by
-- 
2.25.1