linux-kernel - [PATCH 2/5] riscv: __asm_to/copy_from

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Message-ID: <98088fde-cdb2-6410-8d11-7c8ca984d3c3@gmail.com>
Date:   Sat, 19 Jun 2021 20:35:39 +0900
From:   Akira Tsukamoto <akira.tsukamoto@...il.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: [PATCH 2/5] riscv: __asm_to/copy_from_user: Adding byte copy first


Typical load and store loop.
It is used for mainly copying the remainder in one byte at a time.

Signed-off-by: Akira Tsukamoto <akira.tsukamoto@...il.com>
---
 arch/riscv/lib/uaccess.S | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
index da9536e1e9cb..be1810077f9a 100644
--- a/arch/riscv/lib/uaccess.S
+++ b/arch/riscv/lib/uaccess.S
@@ -19,9 +19,39 @@ ENTRY(__asm_copy_from_user)
 	li t6, SR_SUM
 	csrs CSR_STATUS, t6
 
+	/* Save for return value */
+	mv	t5, a2
+
+	/*
+	 * Register allocation for code below:
+	 * a0 - start of uncopied dst
+	 * a1 - start of uncopied src
+	 * a2 - size
+	 * t0 - end of uncopied dst
+	 */
+	add	t0, a0, a2
+	bgtu	a0, t0, 5f
+
+.Lbyte_copy_tail:
+	/*
+	 * Byte copy anything left.
+	 *
+	 * a0 - start of remaining dst
+	 * a1 - start of remaining src
+	 * t0 - end of remaining dst
+	 */
+	bgeu	a0, t0, 5f
+4:
+	fixup lb      a5, 0(a1), 10f
+	addi	a1, a1, 1	/* src */
+	fixup sb      a5, 0(a0), 10f
+	addi	a0, a0, 1	/* dst */
+	bltu	a0, t0, 4b	/* t0 - end of dst */
+
+5:
 	/* Disable access to user memory */
 	csrc CSR_STATUS, t6
-	li a0, 0
+	li	a0, 0
 	ret
 ENDPROC(__asm_copy_to_user)
 ENDPROC(__asm_copy_from_user)
@@ -77,7 +107,7 @@ EXPORT_SYMBOL(__clear_user)
 10:
 	/* Disable access to user memory */
 	csrs CSR_STATUS, t6
-	mv a0, a2
+	mv a0, t5
 	ret
 11:
 	csrs CSR_STATUS, t6
-- 
2.17.1