[PATCH] objtool: Disable stack validation when CROSS_COMPILE is used

[Josh Poimboeuf]

When building with CONFIG_STACK_VALIDATION on a PowerPC host using an
x86 cross-compiler, Stephen Rothwell saw the following objtool build
errors:

    DESCEND  objtool
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/builtin-check.o
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/special.o
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/elf.o
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/objtool.o
    MKDIR    /home/sfr/next/x86_64_allmodconfig/tools/objtool/arch/x86/insn/
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/libstring.o
  elf.c:22:23: fatal error: sys/types.h: No such file or directory
  compilation terminated.
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/exec-cmd.o
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/help.o
  builtin-check.c:28:20: fatal error: string.h: No such file or directory
  compilation terminated.
  objtool.c:28:19: fatal error: stdio.h: No such file or directory
  compilation terminated.

The problem is that objtool was compiled with the cross compiler instead
of the host compiler.  But even if that were fixed, we'd still have a
problem with endianness.  objtool's x86 decoder (copied from
arch/x86/lib/insn.c) assumes that the endianness of the host and target
are the same.  When analyzing a little-endian x86 binary on a big-endian
host, it will get confused and spit out a bunch of false positive
warnings during the build.

Eventually we may want to add endian awareness to x86 objtool, but
that's generally a rare edge case and it's not clear if anybody would
use it.  For now, when a cross-compiler is used, just disable
CONFIG_STACK_VALIDATION and emit a warning.

Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 Makefile               | 12 +++++++++++-
 scripts/Makefile.build |  4 +++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 8cc926f..b59007c 100644
--- a/Makefile
+++ b/Makefile
@@ -998,8 +998,18 @@ prepare0: archprepare FORCE
 # All the preparing..
 prepare: prepare0 prepare-objtool
 
+
+ifdef CONFIG_STACK_VALIDATION
+  ifeq ($(CROSS_COMPILE),)
+    objtool_target := tools/objtool FORCE
+  else
+    $(warning Stack validation is not supported with cross-compilation.  Disabling CONFIG_STACK_VALIDATION!)
+  endif
+endif
+
 PHONY += prepare-objtool
-prepare-objtool: $(if $(CONFIG_STACK_VALIDATION), tools/objtool FORCE)
+prepare-objtool: $(objtool_target)
+
 
 # Generate some files
 # ---------------------------------------------------------------------------
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 130a452..973bb26 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -242,6 +242,7 @@ cmd_record_mcount =						\
 endif
 
 ifdef CONFIG_STACK_VALIDATION
+ifeq ($(CROSS_COMPILE),)
 
 __objtool_obj := $(objtree)/tools/objtool/objtool
 
@@ -260,13 +261,14 @@ objtool_obj = $(if $(patsubst y%,, \
 	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
 	$(__objtool_obj))
 
+endif # CROSS_COMPILE
 endif # CONFIG_STACK_VALIDATION
 
 define rule_cc_o_c
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
 	$(call echo-cmd,cc_o_c) $(cmd_cc_o_c);				  \
 	$(cmd_modversions)						  \
-	$(cmd_objtool)						  \
+	$(cmd_objtool)							  \
 	$(call echo-cmd,record_mcount)					  \
 	$(cmd_record_mcount)						  \
 	scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
-- 
2.4.3