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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 v3 2/3] objtool: check: Support addition to set CFA base
Date:   Wed, 14 Oct 2020 08:38:01 +0100
Message-Id: <20201014073802.436630-3-jthierry@redhat.com>
In-Reply-To: <20201014073802.436630-1-jthierry@redhat.com>
References: <20201014073802.436630-1-jthierry@redhat.com>
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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 | 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