[PATCH v2 5/6] arm64: lib: Disable branch profiling for architecture library code

[Jisheng Zhang <jszhang@kernel.org>]

arch/arm64/Kbuild disables branch profiling through subdir-ccflags-y.
However, arch/arm64/lib/ is built separately through libs-y and does
not inherit that flag.

Consequently, CONFIG_TRACE_BRANCH_PROFILING can introduce explicit
profiling instrumentation into library code, including helpers used
while applying alternatives. noinstr does not suppress instrumentation
inserted by the branch-profiling macros.

Disable branch profiling in arch/arm64/lib/Makefile to extend the
existing arm64 policy to this directory

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Assisted-by: LLM
---
 arch/arm64/lib/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 38ffd359123c..59d714865c00 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -1,5 +1,9 @@
 # SPDX-License-Identifier: GPL-2.0
 
+# Built via libs-y, so the flags in arch/arm64/Kbuild do not reach here.
+# Branch profiling isn't noinstr-safe.
+ccflags-$(CONFIG_TRACE_BRANCH_PROFILING) += -DDISABLE_BRANCH_PROFILING
+
 # KCSAN uses udelay for introducing watchpoint delay; avoid recursion.
 KCSAN_SANITIZE_delay.o := n
 
-- 
2.55.0