[PATCH] Kbuild: Check for CONFIG_READABLE_ASM when building .s targets

[Borislav Petkov <bp@alien8.de>]

From: Borislav Petkov <bp@suse.de>

We do need to look at the asm output of c files for various reasons. In
order to do so, we do make <path-to-filename>.s.

However, it can happen that the Kconfig option which enables the
creation of readable asm CONFIG_READABLE_ASM is disabled. What is more,
we want this option enabled because it indirectly enables the issue of
line numbers in the asm done by gcc's switch -g.

So issue a warning that the asm output might not be optimally readable
if that option is disabled.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
 Makefile               | 2 +-
 scripts/Makefile.build | 7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index e43244263306..d9b505360c2a 100644
--- a/Makefile
+++ b/Makefile
@@ -1513,7 +1513,7 @@ else
 endif
 
 %.s: %.c prepare scripts FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
+	$(Q)$(MAKE) $(build)=$(build-dir) asm_target=$@ $(target-dir)$(notdir $@)
 %.i: %.c prepare scripts FORCE
 	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
 %.o: %.c prepare scripts FORCE
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index bf3e6778cd71..8aaf1c04fe18 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -147,7 +147,12 @@ $(multi-objs-y:.o=.s)   : modname = $(modname-multi)
 $(multi-objs-y:.o=.lst) : modname = $(modname-multi)
 
 quiet_cmd_cc_s_c = CC $(quiet_modtag)  $@
-cmd_cc_s_c       = $(CC) $(c_flags) $(DISABLE_LTO) -fverbose-asm -S -o $@ $<
+cmd_cc_s_c       = $(CC) $(c_flags) $(DISABLE_LTO) -fverbose-asm -S -o $@ $< \
+		   $(if $(findstring $(asm_target),$@),\
+			$(if $(__cmd_cc_s_c_once),,\
+				$(if $(CONFIG_READABLE_ASM),,\
+					$(warning Enable CONFIG_READABLE_ASM for more helpful asm); \
+					$(eval __cmd_cc_s_c_once=1)))) \
 
 $(obj)/%.s: $(src)/%.c FORCE
 	$(call if_changed_dep,cc_s_c)
-- 
2.0.0