objtool: Detect and warn if libelf is missing and don't break the build
With CONFIG_STACK_VALIDATION enabled, if the host system doesn't have
a development version of libelf installed, the build fails with errors
like:
elf.h:22:18: fatal error: gelf.h: No such file or directory compilation terminated.
Instead of failing to build, instead just print a warning and disable
stack validation.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-next@vger.kernel.org
Cc: linux@roeck-us.net
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/8c27fe00face60f42e888ddb3142c97e45223165.1457026550.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/Makefile b/Makefile
index 2c27a01..60b7295 100644
--- a/Makefile
+++ b/Makefile
@@ -995,8 +995,19 @@
# All the preparing..
prepare: prepare0 prepare-objtool
+ifdef CONFIG_STACK_VALIDATION
+ has_libelf := $(shell echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf - &> /dev/null && echo 1 || echo 0)
+ ifeq ($(has_libelf),1)
+ objtool_target := tools/objtool FORCE
+ else
+ $(warning "Cannot use CONFIG_STACK_VALIDATION, please install libelf-dev or elfutils-libelf-devel")
+ SKIP_STACK_VALIDATION := 1
+ export SKIP_STACK_VALIDATION
+ endif
+endif
+
PHONY += prepare-objtool
-prepare-objtool: $(if $(CONFIG_STACK_VALIDATION), tools/objtool FORCE)
+prepare-objtool: $(objtool_target)
# Generate some files
# ---------------------------------------------------------------------------