kbuild: add support for ensuring headers are self-contained

Sometimes it's useful to be able to explicitly ensure certain headers
remain self-contained, i.e. that they are compilable as standalone
units, by including and/or forward declaring everything they depend on.

Add special target header-test-y where individual Makefiles can add
headers to be tested if CONFIG_HEADER_TEST is enabled. This will
generate a dummy C file per header that gets built as part of extra-y.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

2 files changed, 12 insertions, 0 deletions

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index ae9cf740633e..ee0319560513 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -294,6 +294,15 @@ quiet_cmd_cc_lst_c = MKLST   $@
 $(obj)/%.lst: $(src)/%.c FORCE
         $(call if_changed_dep,cc_lst_c)
 
+# Dummy C sources for header test (header-test-y target)
+# ---------------------------------------------------------------------------
+
+quiet_cmd_header_test = HDRTEST $@
+      cmd_header_test = echo "\#include \"$*.h\"" > $@
+
+$(obj)/%.hdrtest.c:
+        $(call cmd,header_test)
+
 # Compile assembler sources (.S)
 # ---------------------------------------------------------------------------
 
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index f1f38c8cdc74..3e630fcaffd1 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -66,6 +66,9 @@ extra-y += $(patsubst %.dtb,%.dt.yaml, $(dtb-y))
 extra-$(CONFIG_OF_ALL_DTBS) += $(patsubst %.dtb,%.dt.yaml, $(dtb-))
 endif
 
+# Test self-contained headers
+extra-$(CONFIG_HEADER_TEST) += $(patsubst %.h,%.hdrtest.o,$(header-test-y))
+
 # Add subdir path
 
 extra-y         := $(addprefix $(obj)/,$(extra-y))