objtool: Make SP memory operation match PUSH/POP semantics

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 <[e-mail]>
Acked-by: Peter Zijlstra (Intel) <[e-mail]>
Signed-off-by: Josh Poimboeuf <[e-mail]>

tools/objtool/check.c

···
 			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) {
 
···
 			    op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
 
 				/* 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);
 			}
···
 			/* 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;