[PATCH v3 2/3] objtool: check: Support addition to set CFA base

[Julien Thierry]

On arm64, the compiler can set the frame pointer either
with a move operation or with and add operation like:

    add (SP + constant), BP

For a simple move operation, the CFA base is changed from SP to BP.
Handle also changing the CFA base when the frame pointer is set with
an addition instruction.

Signed-off-by: Julien Thierry <jthie...@redhat.com>
---
 tools/objtool/check.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 87f10e726a75..815aeb770930 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1898,6 +1898,17 @@ static int update_cfi_state(struct instruction *insn, 
struct cfi_state *cfi,
                                break;
                        }
 
+                       if (!cfi->drap && op->src.reg == CFI_SP &&
+                           op->dest.reg == CFI_BP && cfa->base == CFI_SP &&
+                           check_reg_frame_pos(&regs[CFI_BP], -cfa->offset + 
op->src.offset)) {
+
+                               /* lea disp(%rsp), %rbp */
+                               cfa->base = CFI_BP;
+                               cfa->offset -= op->src.offset;
+                               cfi->bp_scratch = false;
+                               break;
+                       }
+
                        if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
 
                                /* drap: lea disp(%rsp), %drap */
-- 
2.25.4