[tip: objtool/core] objtool: Support addition to set CFA base

[tip: objtool/core] objtool: Support addition to set CFA base

[tip-bot2 for Julien Thierry]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     468af56a7bbaa626da5a4578bedc930d731fba13
Gitweb:        https://git.kernel.org/tip/468af56a7bbaa626da5a4578bedc930d731fba13
Author:        Julien Thierry <jthierry@redhat.com>
AuthorDate:    Wed, 14 Oct 2020 08:38:01 +01:00
Committer:     Josh Poimboeuf <jpoimboe@redhat.com>
CommitterDate: Wed, 13 Jan 2021 18:13:10 -06:00

objtool: Support addition to set CFA base

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 <jthierry@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@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 88210b0..00d00f9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1960,6 +1960,17 @@ 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 */