[tip:x86/asm] objtool: Fix objtool fallthrough detection with function padding

[tip-bot for Josh Poimboeuf]

Commit-ID:  ee97638b5737cc0dba2f12a3bdcda761656b7c01
Gitweb:     http://git.kernel.org/tip/ee97638b5737cc0dba2f12a3bdcda761656b7c01
Author:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Fri, 11 Aug 2017 12:24:15 -0500
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 21 Aug 2017 16:06:05 +0200

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 <fengguang.wu@xxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/43e7aae9a7a7710cd6df597fa9dc501da4ba0602.1502472193.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 tools/objtool/check.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 1737592..3dffeb9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1536,15 +1536,15 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 	while (1) {
 		next_insn = next_insn_same_sec(file, insn);
 
-		if (file->c_file && insn->func) {
-			if (func && func != insn->func) {
-				WARN("%s() falls through to next function %s()",
-				     func->name, insn->func->name);
-				return 1;
-			}
+
+		if (file->c_file && func && insn->func && func != insn->func) {
+			WARN("%s() falls through to next function %s()",
+			     func->name, insn->func->name);
+			return 1;
 		}
 
-		func = insn->func;
+		if (insn->func)
+			func = insn->func;
 
 		if (func && insn->ignore) {
 			WARN_FUNC("BUG: why am I validating an ignored function?",