[PATCH v3 3/3] objtool: check: Make SP memory operation match PUSH/POP semantics

[Julien Thierry]

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@xxxxxxxxxx>
---
 tools/objtool/check.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 815aeb770930..32ee9902ade2 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2003,6 +2003,14 @@ 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 &&
+			    op->dest.reg == CFI_BP) {
+
+				/* 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) {
 
@@ -2024,6 +2032,12 @@ 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;
@@ -2101,6 +2115,12 @@ 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->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;
-- 
2.25.4