[U-Boot] [PATCH] dts/Makefile: Turn off system-/gcc-specific predefined macros

[Horst Kronstorfer]

Add '-undef' to DTS_CPPFLAGS to avoid unwanted expansion of dts content
that matches system-specific or gcc-specific predefined macros.

Example: A number of PowerPC related *.dts files in the kernel define a
property named 'linux,network-index' which (w/o '-undef') is expanded to
'1,network-index' by the preprocessor because of '#define linux 1.'

With '-undef' in place only the standard predefined macros are visible:

 $ gcc -dM -E -undef - </dev/null
 #define __STDC_HOSTED__ 1
 #define __STDC__ 1

Signed-off-by: Horst Kronstorfer <hkronsto at frequentis.com>
---
 dts/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dts/Makefile b/dts/Makefile
index 402dfe1..3c6bc18 100644
--- a/dts/Makefile
+++ b/dts/Makefile
@@ -36,7 +36,7 @@ $(error Your architecture does not have device tree support enabled. \
 Please define CONFIG_ARCH_DEVICE_TREE))
 
 # We preprocess the device tree file provide a useful define
-DTS_CPPFLAGS := -DARCH_CPU_DTS=\"$(SRCTREE)/arch/$(ARCH)/dts/$(CONFIG_ARCH_DEVICE_TREE).dtsi\"
+DTS_CPPFLAGS := -undef -DARCH_CPU_DTS=\"$(SRCTREE)/arch/$(ARCH)/dts/$(CONFIG_ARCH_DEVICE_TREE).dtsi\"
 
 all:	$(obj).depend $(LIB)
 
-- 
1.7.11.2