From aafeb14e9da29e323b0605f8f1bae0d45d5f3acf Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed, 3 Feb 2021 12:02:17 +0100
Subject: [PATCH] objtool: Support stack-swizzle
Natively support the stack swizzle pattern:
mov %rsp, (%[tos])
mov %[tos], %rsp
...
pop %rsp
It uses the vals[] array to link the first two stack-ops, and detect
the SP to SP_INDIRECT swizzle.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
tools/objtool/check.c | 45 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5f056ddab4fa2..62cd211ec45c9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1945,6 +1945,38 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
cfa->offset = -cfi->vals[op->src.reg].offset;
cfi->stack_size = cfa->offset;
+ } else if (cfa->base == CFI_SP &&
+ cfi->vals[op->src.reg].base == CFI_SP_INDIRECT &&
+ cfi->vals[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: we set base to SP_INDIRECT
+ * here and preserve offset. Therefore
+ * when the unwinder reaches ToS it
+ * will dereference SP and then add the
+ * offset to find the next frame, IOW:
+ * (%rsp) + offset.
+ */
+ cfa->base = CFI_SP_INDIRECT;
+
} else {
cfa->base = CFI_UNDEFINED;
cfa->offset = 0;
@@ -2047,6 +2079,13 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
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 */
@@ -2193,6 +2232,12 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
/* mov reg, disp(%rsp) */
save_reg(cfi, op->src.reg, CFI_CFA,
op->dest.offset - cfi->stack_size);
+
+ } else if (op->src.reg == CFI_SP && op->dest.offset == 0) {
+
+ /* mov %rsp, (%reg); # setup a stack swizzle. */
+ cfi->vals[op->dest.reg].base = CFI_SP_INDIRECT;
+ cfi->vals[op->dest.reg].offset = cfa->offset;
}
break;
--
GitLab