rewind_stack_do_exit()
UNWIND_HINT_FUNC
/* Prevent any naive code from trying to unwind to our caller. */
xorl %ebp, %ebp
movq PER_CPU_VAR(cpu_current_top_of_stack), %rax
leaq -PTREGS_SIZE(%rax), %rsp
UNWIND_HINT_REGS
call do_exit
Does unspeakable things to the stack, which objtool currently fails to
detect due to a limitation in instruction decoding. This will be
rectified after which the above will result in:
arch/x86/entry/entry_64.o: warning: objtool: .text+0xab: unsupported stack
register modification
Allow the UNWIND_HINT on the next instruction to suppress this, it
will overwrite the state anyway.
Suggested-by: Josh Poimboeuf <jpoim...@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
tools/objtool/check.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1918,8 +1918,9 @@ static void restore_reg(struct cfi_state
* 41 5d pop %r13
* c3 retq
*/
-static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
- struct stack_op *op)
+static int update_cfi_state(struct instruction *insn,
+ struct instruction *next_insn,
+ struct cfi_state *cfi, struct stack_op *op)
{
struct cfi_reg *cfa = &cfi->cfa;
struct cfi_reg *regs = cfi->regs;
@@ -2106,7 +2107,7 @@ static int update_cfi_state(struct instr
break;
}
- if (op->dest.reg == cfi->cfa.base) {
+ if (op->dest.reg == cfi->cfa.base && !(next_insn &&
next_insn->hint)) {
WARN_FUNC("unsupported stack register
modification",
insn->sec, insn->offset);
return -1;
@@ -2378,13 +2379,15 @@ static int propagate_alt_cfi(struct objt
return 0;
}
-static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
+static int handle_insn_ops(struct instruction *insn,
+ struct instruction *next_insn,
+ struct insn_state *state)
{
struct stack_op *op;
list_for_each_entry(op, &insn->stack_ops, list) {
- if (update_cfi_state(insn, &state->cfi, op))
+ if (update_cfi_state(insn, next_insn, &state->cfi, op))
return 1;
if (op->dest.type == OP_DEST_PUSHF) {
@@ -2678,7 +2681,7 @@ static int validate_branch(struct objtoo
return 0;
}
- if (handle_insn_ops(insn, &state))
+ if (handle_insn_ops(insn, next_insn, &state))
return 1;
switch (insn->type) {
