kcov: don't instrument with UBSAN

Both KCOV and UBSAN use compiler instrumentation.  If UBSAN detects a bug
in KCOV, it may cause infinite recursion via printk and other common
functions.  We already don't instrument KCOV with KASAN/KCSAN for this
reason, don't instrument it with UBSAN as well.

As a side effect this also resolves the following gcc warning:

conflicting types for built-in function '__sanitizer_cov_trace_switch';
expected 'void(long unsigned int, void *)'
[-Wbuiltin-declaration-mismatch]

It's only reported when kcov.c is compiled with any of the sanitizers
enabled.  Size of the arguments is correct, it's just that gcc uses 'long'
on 64-bit arches and 'long long' on 32-bit arches, while kernel type is
always 'long long'.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Dmitry Vyukov <[email protected]>
Reported-by: Stephen Rothwell <[email protected]>
Suggested-by: Marco Elver <[email protected]>
Acked-by: Marco Elver <[email protected]>
Reviewed-by: Andrey Konovalov <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/Makefile

@@ -34,8 +34,11 @@ KCOV_INSTRUMENT_extable.o := n
 KCOV_INSTRUMENT_stacktrace.o := n
 # Don't self-instrument.
 KCOV_INSTRUMENT_kcov.o := n
+# If sanitizers detect any issues in kcov, it may lead to recursion
+# via printk, etc.
 KASAN_SANITIZE_kcov.o := n
 KCSAN_SANITIZE_kcov.o := n
+UBSAN_SANITIZE_kcov.o := n
 CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack) -fno-stack-protector
 
 obj-y += sched/