x32: Warn and disable rather than error if binutils too old

If X32 is enabled in .config, but the binutils can't build it, issue a
warning and disable the feature rather than erroring out.

In order to support this, have CONFIG_X86_X32 be the option set in
Kconfig, and CONFIG_X86_X32_ABI be the option set by the Makefile when
it is enabled and binutils has been found to be functional.

Requested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: H. J. Lu <hjl.tools@gmail.com>
Link: http://lkml.kernel.org/r/1329696488-16970-1-git-send-email-hpa@zytor.com

2 files changed, 18 insertions, 2 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c9d6c9ed27e5..e2b38b4bffdc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2175,7 +2175,7 @@ config IA32_AOUT
         ---help---
           Support old a.out binaries in the 32bit emulation.
 
-config X86_X32_ABI
+config X86_X32
         bool "x32 ABI for 64-bit mode (EXPERIMENTAL)"
         depends on X86_64 && IA32_EMULATION && EXPERIMENTAL
         ---help---
@@ -2190,7 +2190,7 @@ config X86_X32_ABI
 
 config COMPAT
         def_bool y
-        depends on IA32_EMULATION || X86_X32_ABI
+        depends on IA32_EMULATION || X86_X32
 
 config COMPAT_FOR_U64_ALIGNMENT
         def_bool COMPAT
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 209ba1294592..31bb1eb1216a 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -82,6 +82,22 @@ ifdef CONFIG_CC_STACKPROTECTOR
         endif
 endif
 
+ifdef CONFIG_X86_X32
+        x32_ld_ok := $(call try-run,\
+                        /bin/echo -e '1: .quad 1b' | \
+                        $(CC) $(KBUILD_AFLAGS) -c -xassembler -o "$$TMP" - && \
+                        $(OBJCOPY) -O elf32-x86-64 "$$TMP" "$$TMPO" && \
+                        $(LD) -m elf32_x86_64 "$$TMPO" -o "$$TMP",y,n)
+        ifeq ($(x32_ld_ok),y)
+                CONFIG_X86_X32_ABI := y
+                KBUILD_AFLAGS += -DCONFIG_X86_X32_ABI
+                KBUILD_CFLAGS += -DCONFIG_X86_X32_ABI
+        else
+                $(warning CONFIG_X86_X32 enabled but no binutils support)
+        endif
+endif
+export CONFIG_X86_X32_ABI
+
 # Don't unroll struct assignments with kmemcheck enabled
 ifeq ($(CONFIG_KMEMCHECK),y)
         KBUILD_CFLAGS += $(call cc-option,-fno-builtin-memcpy)