[PATCH 2/3] Automatically set CONFIG_BUILD_ELF64

[Franck Bui-Huu <vagabon.xyz@gmail.com>]

From: Franck Bui-Huu <fbuihuu@gmail.com>

We do not rely on user anymore to setup this config correctly.
Instead we make our choice depending on the load address.

If we want to force Kbuild to use ELF64 format whatever
the load address we can still do:

        $ make BUILD_ELF32=no

Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
---
 arch/mips/Kconfig  |   15 ---------------
 arch/mips/Makefile |   23 ++++++++++++++++++++---
 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 54acbf5..89020b6 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2009,21 +2009,6 @@ source "fs/Kconfig.binfmt"
 config TRAD_SIGNALS
 	bool
 
-config BUILD_ELF64
-	bool "Use 64-bit ELF format for building"
-	depends on 64BIT
-	help
-	  A 64-bit kernel is usually built using the 64-bit ELF binary object
-	  format as it's one that allows arbitrary 64-bit constructs.  For
-	  kernels that are loaded within the KSEG compatibility segments the
-	  32-bit ELF format can optionally be used resulting in a somewhat
-	  smaller binary, but this option is not explicitly supported by the
-	  toolchain and since binutils 2.14 it does not even work at all.
-
-	  Say Y to use the 64-bit format or N to use the 32-bit one.
-
-	  If unsure say Y.
-
 config BINFMT_IRIX
 	bool "Include IRIX binary compatibility"
 	depends on CPU_BIG_ENDIAN && 32BIT && BROKEN
diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index 4240ca1..626771c 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -60,9 +60,6 @@ vmlinux-32		= vmlinux.32
 vmlinux-64		= vmlinux
 
 cflags-y		+= -mabi=64
-ifndef CONFIG_BUILD_ELF64
-cflags-y		+= $(call cc-option,-msym32)
-endif
 endif
 
 
@@ -614,6 +611,26 @@ else
 JIFFIES			= jiffies_64
 endif
 
+#
+# Automatically detect the build format. By default we choose
+# the elf format according to the load address.
+# We can always force a build with a 64-bits symbol format by
+# passing 'BUILD_ELF32=no' option to the make's command line.
+#
+ifdef CONFIG_64BIT
+  ifndef BUILD_ELF32
+    ifeq ($(shell expr $(load-y) \< 0xffffffff80000000), 0)
+      BUILD_ELF32 = y
+    endif
+  endif
+
+  ifeq ("$(BUILD_ELF32)", "y")
+    cflags-y += -msym32
+  else
+    cflags-y += -DCONFIG_BUILD_ELF64
+  endif
+endif # CONFIG_64BIT
+
 AFLAGS		+= $(cflags-y)
 CFLAGS		+= $(cflags-y)
 
-- 
1.4.4.3.ge6d4