Natively support the stack swizzle pattern:
mov %rsp, (%[tos])
mov %[tos], %rsp
...
pop %rsp
with the constraint that %[tos] must be !arch_callee_saved_reg().
It uses the (newly minted) scratch regs to link the first two
stack-ops, and detect the SP to SP_INDIRECT swizzle.
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
tools/objtool/check.c | 43 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 43 insertions(+)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1937,6 +1937,34 @@ static int update_cfi_state(struct instr
cfa->offset =
-cfi->vals[op->src.reg].offset;
cfi->stack_size = cfa->offset;
+ } else if (cfa->base == CFI_SP &&
+ cfi->regs[op->src.reg].base ==
CFI_SP_INDIRECT &&
+ cfi->regs[op->src.reg].offset ==
cfa->offset) {
+
+ /*
+ * Stack swizzle:
+ *
+ * 1: mov %rsp, (%[tos])
+ * 2: mov %[tos], %rsp
+ * ...
+ * 3: pop %rsp
+ *
+ * Where:
+ *
+ * 1 - places a pointer to the previous
+ * stack at the Top-of-Stack of the
+ * new stack.
+ *
+ * 2 - switches to the new stack.
+ *
+ * 3 - pops the Top-of-Stack to restore
+ * the original stack.
+ *
+ * Note:
+ * %[tos] must not be a callee saved reg
+ */
+ cfa->base = CFI_SP_INDIRECT;
+
} else {
cfa->base = CFI_UNDEFINED;
cfa->offset = 0;
@@ -2028,6 +2056,13 @@ static int update_cfi_state(struct instr
case OP_SRC_POP:
case OP_SRC_POPF:
+ if (op->dest.reg == CFI_SP && cfa->base ==
CFI_SP_INDIRECT) {
+
+ /* pop %rsp; # restore from a stack swizzle */
+ cfa->base = CFI_SP;
+ break;
+ }
+
if (!cfi->drap && op->dest.reg == cfa->base) {
/* pop %rbp */
@@ -2154,6 +2189,14 @@ static int update_cfi_state(struct instr
/* mov reg, disp(%rsp) */
save_reg(cfi, op->src.reg, CFI_CFA,
op->dest.offset - cfi->cfa.offset);
+
+ } else if (op->src.reg == CFI_SP && op->dest.offset == 0) {
+
+ /* mov %rsp, (%reg); # setup a stack swizzle. */
+ if (!arch_callee_saved_reg(op->dest.reg)) {
+ __save_reg(cfi, op->dest.reg, CFI_SP_INDIRECT,
cfi->cfa.offset);
+ skip_wipe = true;
+ }
}
break;
