objtool: Fix objtool fallthrough detection with function padding

objtool: Fix objtool fallthrough detection with function padding

When GCC adds NOP padding between functions, those NOPs aren't
associated with a function symbol, which breaks objtool's detection of a
function falling through to another function.  Instead it shows
confusing errors like:

  drivers/mtd/chips/cfi_util.o: warning: objtool: cfi_qry_mode_on()+0x8b: return with modified stack frame
  drivers/mtd/chips/cfi_util.o: warning: objtool: cfi_qry_mode_on()+0x0: stack state mismatch: cfa1=-4-32 cfa2=7+8
  drivers/mtd/chips/cfi_cmdset_0002.o: warning: objtool: fixup_use_fwh_lock()+0x8: unknown stack-related register move
  drivers/mtd/chips/cfi_cmdset_0002.o: warning: objtool: fixup_use_fwh_lock()+0x0: stack state mismatch: cfa1=6+16 cfa2=7+8
  drivers/mtd/chips/cfi_cmdset_0002.o: warning: objtool: do_otp_write()+0xa: unsupported stack pointer realignment
  drivers/mtd/chips/cfi_cmdset_0002.o: warning: objtool: do_otp_write()+0x0: stack state mismatch: cfa1=-4-40 cfa2=7+8

Reported-by: kbuild test robot <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/43e7aae9a7a7710cd6df597fa9dc501da4ba0602.1502472193.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>