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Subject[PATCH 3/3] objtool: check: Make SP memory operation match PUSH/POP semantics
Date
Architectures without PUSH/POP instructions will always access the stack
though memory operations (SRC/DEST_INDIRECT). Make those operations have
the same effect on the CFA as PUSH/POP, with no stack pointer
modification.

Signed-off-by: Julien Thierry <jthierry@redhat.com>
---
tools/objtool/check.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f45991c2db41..7ff87fa3caec 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2005,6 +2005,13 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
break;

case OP_SRC_REG_INDIRECT:
+ if (!cfi->drap && op->dest.reg == cfa->base) {
+
+ /* mov disp(%rsp), %rbp */
+ cfa->base = CFI_SP;
+ cfa->offset = cfi->stack_size;
+ }
+
if (cfi->drap && op->src.reg == CFI_BP &&
op->src.offset == cfi->drap_offset) {

@@ -2026,6 +2033,11 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
/* mov disp(%rbp), %reg */
/* mov disp(%rsp), %reg */
restore_reg(cfi, op->dest.reg);
+ } else if (op->src.reg == CFI_SP &&
+ op->src.offset == regs[op->dest.reg].offset + cfi->stack_size) {
+
+ /* mov disp(%rsp), %reg */
+ restore_reg(cfi, op->dest.reg);
}

break;
@@ -2103,6 +2115,11 @@ 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->cfa.offset);
+ } else if (op->dest.reg == CFI_SP) {
+
+ /* mov reg, disp(%rsp) */
+ save_reg(cfi, op->src.reg, CFI_CFA,
+ op->dest.offset - cfi->stack_size);
}

break;
--
2.21.3
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