[PATCHv2] arm64: avoid instrumenting atomic_ll_sc.o

[Mark Rutland]

Our out-of-line atomics are built with a special calling convention,
preventing pointless stack spilling, and allowing us to patch call sites
with ARMv8.1 atomic instructions.

Instrumentation inserted by the compiler may result in calls to
functions not following this special calling convention, resulting in
registers being unexpectedly clobbered, and various problems resulting
from this.

For example, if a kernel is built with KCOV and ARM64_LSE_ATOMICS, the
compiler inserts calls to __sanitizer_cov_trace_pc in the prologues of
the atomic functions. This has been observed to result in spurious
cmpxchg failures, leading to a hang early on in the boot process.

This patch avoids such issues by preventing instrumentation of our
out-of-line atomics.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
---
 arch/arm64/lib/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

Since v1 [1]:
* rebase to v4.17-rc2

To test this I built a v4.17-rc2 kernel with this applied, with GCOV, KASAN,
KCOV, UBSAN, CONFIG_FTRACE, and CONFIG_FUNCTION_TRACER enabled, and verified
the disassembly of atomic_ll_sc.o was safe.

Mark.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-September/533105.html

diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 0ead8a1d1679..137710f4dac3 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -19,5 +19,9 @@ CFLAGS_atomic_ll_sc.o	:= -fcall-used-x0 -ffixed-x1 -ffixed-x2		\
 		   -fcall-saved-x13 -fcall-saved-x14 -fcall-saved-x15	\
 		   -fcall-saved-x18 -fomit-frame-pointer
 CFLAGS_REMOVE_atomic_ll_sc.o := -pg
+GCOV_PROFILE_atomic_ll_sc.o	:= n
+KASAN_SANITIZE_atomic_ll_sc.o	:= n
+KCOV_INSTRUMENT_atomic_ll_sc.o	:= n
+UBSAN_SANITIZE_atomic_ll_sc.o	:= n
 
 lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o
-- 
2.11.0