Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Julien Thierry <jthierry@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     jpoimboe@redhat.com, peterz@infradead.org, mbenes@suse.cz,
        raphael.gault@arm.com, benh@kernel.crashing.org,
        Julien Thierry <jthierry@redhat.com>
Subject: [PATCH v2 2/3] objtool: check: Support addition to set CFA base
Date:   Mon, 28 Sep 2020 10:36:30 +0100
Message-Id: <20200928093631.210610-3-jthierry@redhat.com>
In-Reply-To: <20200928093631.210610-1-jthierry@redhat.com>
References: <20200928093631.210610-1-jthierry@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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>
---
 tools/objtool/check.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 50b3a4504db1..9f7a14a24a65 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1901,6 +1901,19 @@ 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 + STACKFRAME_SIZE,
+						STACKFRAME_BP_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