x86: Ignore stack unwinding in KCOV

Stack unwinding produces large amounts of uninteresting coverage.
It's called from KASAN kmalloc/kfree hooks, fault injection, etc.
It's not particularly useful and is not a function of system call args.
Ignore that code.

Signed-off-by: Dmitry Vyukov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Alexander Potapenko <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Reviewed-by: Andrey Konovalov <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/all/eaf54b8634970b73552dcd38bf9be6ef55238c10.1718092070.git.dvyukov@google.com

Author: dvyukov

arch/x86/kernel/Makefile

@@ -35,6 +35,14 @@ KMSAN_SANITIZE_nmi.o					:= n
 # If instrumentation of the following files is enabled, boot hangs during
 # first second.
 KCOV_INSTRUMENT_head$(BITS).o				:= n
+# These are called from save_stack_trace() on debug paths,
+# and produce large amounts of uninteresting coverage.
+KCOV_INSTRUMENT_stacktrace.o				:= n
+KCOV_INSTRUMENT_dumpstack.o				:= n
+KCOV_INSTRUMENT_dumpstack_$(BITS).o			:= n
+KCOV_INSTRUMENT_unwind_orc.o				:= n
+KCOV_INSTRUMENT_unwind_frame.o				:= n
+KCOV_INSTRUMENT_unwind_guess.o				:= n
 
 CFLAGS_irq.o := -I $(src)/../include/asm/trace