tools build: Fix objtool build with ARCH=x86_64

The objtool build fails in a cross-compiled environment on a non-x86
host with "ARCH=x86_64":

  tools/objtool/objtool-in.o: In function `decode_instructions':
  tools/objtool/builtin-check.c:276: undefined reference to `arch_decode_instruction'

We could override the ARCH environment variable and change it back to
x86, similar to what the objtool Makefile was doing before; but it's
tricky to override environment variables consistently.

Instead, take a similar approach used by the Linux top-level Makefile
and introduce a SRCARCH Makefile variable which evaluates to "x86" when
ARCH is either "x86_64" or "x86".

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160722191920.ej62fnspnqurbaa7@treble
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/tools/objtool/Build b/tools/objtool/Build
index 2457916a3943..d6cdece5e58b 100644
--- a/tools/objtool/Build
+++ b/tools/objtool/Build
@@ -1,4 +1,4 @@
-objtool-y += arch/$(ARCH)/
+objtool-y += arch/$(SRCARCH)/
 objtool-y += builtin-check.o
 objtool-y += elf.o
 objtool-y += special.o