A Clang-built kernel is showing the following warning:
arch/x86/kernel/platform-quirks.o: warning: objtool:
x86_early_init_platform_quirks()+0x84: unreachable instruction
That corresponds to this code:
7e: 0f 85 00 00 00 00 jne 84 <x86_early_init_platform_quirks+0x84>
80: R_X86_64_PC32 __x86_indirect_thunk_r11-0x4
84: c3 retq
This is a conditional retpoline sibling call, which is now possible
thanks to retpolines. Objtool hasn't seen that before. It's
incorrectly interpreting the conditional jump as an unconditional
dynamic jump.
Reported-by: Nick Desaulniers <ndesaulni...@google.com>
Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
---
tools/objtool/arch.h | 1 +
tools/objtool/check.c | 12 ++++++++++--
2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index 50448c0c4bca..ced3765c4f44 100644
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -15,6 +15,7 @@ enum insn_type {
INSN_JUMP_CONDITIONAL,
INSN_JUMP_UNCONDITIONAL,
INSN_JUMP_DYNAMIC,
+ INSN_JUMP_DYNAMIC_CONDITIONAL,
INSN_CALL,
INSN_CALL_DYNAMIC,
INSN_RETURN,
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5a237fc05cdc..a8411355a80d 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -575,7 +575,11 @@ static int add_jump_destinations(struct objtool_file *file)
* Retpoline jumps are really dynamic jumps in
* disguise, so convert them accordingly.
*/
- insn->type = INSN_JUMP_DYNAMIC;
+ if (insn->type == INSN_JUMP_UNCONDITIONAL)
+ insn->type = INSN_JUMP_DYNAMIC;
+ else
+ insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
+
insn->retpoline_safe = true;
continue;
} else {
@@ -2114,13 +2118,17 @@ static int validate_branch(struct objtool_file *file,
struct symbol *func,
break;
case INSN_JUMP_DYNAMIC:
+ case INSN_JUMP_DYNAMIC_CONDITIONAL:
if (func && is_sibling_call(insn)) {
ret = validate_sibling_call(insn, &state);
if (ret)
return ret;
}
- return 0;
+ if (insn->type == INSN_JUMP_DYNAMIC)
+ return 0;
+
+ break;
case INSN_CONTEXT_SWITCH:
if (func && (!next_insn || !next_insn->hint)) {
--
2.20.1
