[U-Boot] [PATCH v2 3/3] kbuild: redefine __FILE__ as relative path from $(srctree) if possible

[Masahiro Yamada]

Since Kbuild runs in the objtree, __FILE__ can be a very long path
depending of $(srctree).

If objtree is a child of srctree, the situation is a bit better.
($(srctree) is "..")

For other cases of out-of-tree build, filenames in WARN_ON() etc. are
still an absolute path.  It also means the U-Boot image depends on
where it was built.

Here, the idea is to redefine __FILE__ as the relative path from
$(srctree), but doing so causes a compiler warning:
  warning: "__FILE__" redefined [-Wbuiltin-macro-redefined]

The option -Wno-builtin-macro-redefined can suppress it, but it is
only recognized by GCC 4.4 or newer.  Redefine __FILE__ only when
possible.

Signed-off-by: Masahiro Yamada <yamada.masahiro at socionext.com>
---

Changes in v2:
  - Rephrase comments for clarification
  - Fix a typo

 Makefile | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Makefile b/Makefile
index 888486b..1ff312a 100644
--- a/Makefile
+++ b/Makefile
@@ -1334,6 +1334,15 @@ prepare0: archprepare FORCE
 # All the preparing..
 prepare: prepare0
 
+# If possible, redefine __FILE__ as relative path from $(srctree).
+# $$ is needed to evaluate the variables in sub-directories.
+ifeq ($(call cc-option-yn,-Wno-builtin-macro-redefined),y)
+KBUILD_CFLAGS   += -Wno-builtin-macro-redefined \
+		   -D__FILE__=$$(call stringify,$$(src)/$$(notdir $$<))
+endif
+# CAUTION: Do not add any reference to KBUILD_CFLAGS below this line.
+# $(call cc-option,...) etc. may return wrong result.
+
 # Generate some files
 # ---------------------------------------------------------------------------
 
-- 
2.7.4