[PATCH] kbuild: Allow gcov to be enabled on the command line

[Kent Overstreet]

This allows gcov to be enabled for a particular kernel source
subdirectory on the command line, without editing makefiles, like so:

  make GCOV_PROFILE_fs_bcachefs=y

Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Nicolas Schier <nicolas@xxxxxxxxx>
Cc: linux-kbuild@xxxxxxxxxxxxxxx
Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
---
 scripts/Kbuild.include | 10 ++++++++++
 scripts/Makefile.lib   |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 7778cc97a4e0..5341736f2e30 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -277,3 +277,13 @@ ifneq ($(and $(filter notintermediate, $(.FEATURES)),$(filter-out 4.4,$(MAKE_VER
 else
 .SECONDARY:
 endif
+
+ # expand_parents(a/b/c) = a/b/c a/b a
+expand_parents2 = $(if $(subst .,,$(1)),$(call expand_parents,$(1)),)
+expand_parents  = $(1) $(call expand_parents2,$(patsubst %/,%,$(dir $(1))))
+
+# flatten_dirs(a/b/c) = a_b_c a_b a
+flatten_dirs = $(subst /,_,$(call expand_parents,$(1)))
+
+# eval_vars(X_,a/b/c) = $(X_a_b_c) $(X_a_b) $(X_a)
+eval_vars = $(foreach var,$(call flatten_dirs,$(2)),$($(1)$(var)))
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 1a965fe68e01..0b4581a8bc33 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -148,7 +148,7 @@ _cpp_flags     = $(KBUILD_CPPFLAGS) $(cppflags-y) $(CPPFLAGS_$(target-stem).lds)
 #
 ifeq ($(CONFIG_GCOV_KERNEL),y)
 _c_flags += $(if $(patsubst n%,, \
-		$(GCOV_PROFILE_$(basetarget).o)$(GCOV_PROFILE)$(CONFIG_GCOV_PROFILE_ALL)), \
+		$(GCOV_PROFILE_$(basetarget).o)$(call eval_vars,GCOV_PROFILE_,$(src))$(GCOV_PROFILE)$(CONFIG_GCOV_PROFILE_ALL)), \
 		$(CFLAGS_GCOV))
 endif
 
-- 
2.42.0