Objtool tries to silence 'unreachable instruction' warnings when it
detects gcov is enabled, because gcov produces a lot of unreachable
instructions and they don't really matter.
However, the 0-day bot is still reporting some unreachable instruction
warnings with CONFIG_GCOV_KERNEL=y on GCC 4.6.4.
As it turns out, objtool's gcov detection doesn't work with older
versions of GCC because they don't create a bunch of symbols with the
'gcov.' prefix like newer versions of GCC do.
Move the gcov check out of objtool and instead just create a new
'--no-unreachable' flag which can be passed in by the kernel Makefile
when CONFIG_GCOV_KERNEL is defined.
Also rename the 'nofp' variable to 'no_fp' for consistency with the new
'no_unreachable' variable.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9cfffb1168 ("objtool: Skip all "unreachable instruction" warnings for gcov kernels")
Link: http://lkml.kernel.org/r/c243dc78eb2ffdabb6e927844dea39b6033cd395.1500939244.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
With some configs, objtool reports the following warning:
arch/x86/kernel/ftrace.o: warning: objtool: ftrace_modify_code_direct()+0x2d: sibling call from callable instruction with modified stack frame
The instruction it's complaining about isn't actually a sibling call.
It's just a normal jump to an address inside the function. Objtool
thought it was a sibling call because the instruction's jump_dest wasn't
initialized because the function was supposed to be ignored due to its
use of sync_core().
Objtool ended up validating the function instead of ignoring it because
it didn't properly recognize a sibling call to the function. So fix the
sibling call logic. Also add a warning to catch ignored functions being
validated so we'll get a more useful error message next time.
Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/96cc8ecbcdd8cb29ddd783817b4af918a6a171b0.1499437107.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Previously, objtool ignored functions which have the IRET instruction
in them. That's because it assumed that such functions know what
they're doing with respect to frame pointers.
With the new "objtool 2.0" changes, it stopped ignoring such functions,
and started complaining about them:
arch/x86/kernel/alternative.o: warning: objtool: do_sync_core()+0x1b: unsupported instruction in callable function
arch/x86/kernel/alternative.o: warning: objtool: text_poke()+0x1a8: unsupported instruction in callable function
arch/x86/kernel/ftrace.o: warning: objtool: do_sync_core()+0x16: unsupported instruction in callable function
arch/x86/kernel/cpu/mcheck/mce.o: warning: objtool: machine_check_poll()+0x166: unsupported instruction in callable function
arch/x86/kernel/cpu/mcheck/mce.o: warning: objtool: do_machine_check()+0x147: unsupported instruction in callable function
Silence those warnings for now. They can be re-enabled later, once we
have unwind hints which will allow the code to annotate the IRET usages.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Fixes: baa41469a7 ("objtool: Implement stack validation 2.0")
Link: http://lkml.kernel.org/r/20170630140934.mmwtpockvpupahro@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
