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Subject[tip:core/urgent] objtool: Fix sibling call detection logic
Commit-ID:  4855022a52262411ce38c93dec4cb1470705c0a0
Gitweb: http://git.kernel.org/tip/4855022a52262411ce38c93dec4cb1470705c0a0
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Fri, 7 Jul 2017 09:19:42 -0500
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 8 Jul 2017 10:29:48 +0200

objtool: Fix sibling call detection logic

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>
---
tools/objtool/check.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index fea2221..2c6d748 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1371,6 +1371,12 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,

func = insn->func;

+ if (func && insn->ignore) {
+ WARN_FUNC("BUG: why am I validating an ignored function?",
+ sec, insn->offset);
+ return -1;
+ }
+
if (insn->visited) {
if (!!insn_state_match(insn, &state))
return 1;
@@ -1426,16 +1432,19 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,

case INSN_JUMP_CONDITIONAL:
case INSN_JUMP_UNCONDITIONAL:
- if (insn->jump_dest) {
+ if (insn->jump_dest &&
+ (!func || !insn->jump_dest->func ||
+ func == insn->jump_dest->func)) {
ret = validate_branch(file, insn->jump_dest,
state);
if (ret)
return 1;
+
} else if (func && has_modified_stack_frame(&state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
sec, insn->offset);
return 1;
- } /* else it's a sibling call */
+ }

if (insn->type == INSN_JUMP_UNCONDITIONAL)
return 0;
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