RISC-V: Generic library routines and assembly

This patch contains code that is more specific to the RISC-V ISA than it
is to Linux.  It contains string and math operations, C wrappers for
various assembly instructions, stack walking code, and uaccess.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

arch/riscv/lib/uaccess.S

@@ -0,0 +1,117 @@
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm/csr.h>
+
+	.altmacro
+	.macro fixup op reg addr lbl
+	LOCAL _epc
+_epc:
+	\op \reg, \addr
+	.section __ex_table,"a"
+	.balign RISCV_SZPTR
+	RISCV_PTR _epc, \lbl
+	.previous
+	.endm
+
+ENTRY(__copy_user)
+
+	/* Enable access to user memory */
+	li t6, SR_SUM
+	csrs sstatus, t6
+
+	add a3, a1, a2
+	/* Use word-oriented copy only if low-order bits match */
+	andi t0, a0, SZREG-1
+	andi t1, a1, SZREG-1
+	bne t0, t1, 2f
+
+	addi t0, a1, SZREG-1
+	andi t1, a3, ~(SZREG-1)
+	andi t0, t0, ~(SZREG-1)
+	/*
+	 * a3: terminal address of source region
+	 * t0: lowest XLEN-aligned address in source
+	 * t1: highest XLEN-aligned address in source
+	 */
+	bgeu t0, t1, 2f
+	bltu a1, t0, 4f
+1:
+	fixup REG_L, t2, (a1), 10f
+	fixup REG_S, t2, (a0), 10f
+	addi a1, a1, SZREG
+	addi a0, a0, SZREG
+	bltu a1, t1, 1b
+2:
+	bltu a1, a3, 5f
+
+3:
+	/* Disable access to user memory */
+	csrc sstatus, t6
+	li a0, 0
+	ret
+4: /* Edge case: unalignment */
+	fixup lbu, t2, (a1), 10f
+	fixup sb, t2, (a0), 10f
+	addi a1, a1, 1
+	addi a0, a0, 1
+	bltu a1, t0, 4b
+	j 1b
+5: /* Edge case: remainder */
+	fixup lbu, t2, (a1), 10f
+	fixup sb, t2, (a0), 10f
+	addi a1, a1, 1
+	addi a0, a0, 1
+	bltu a1, a3, 5b
+	j 3b
+ENDPROC(__copy_user)
+
+
+ENTRY(__clear_user)
+
+	/* Enable access to user memory */
+	li t6, SR_SUM
+	csrs sstatus, t6
+
+	add a3, a0, a1
+	addi t0, a0, SZREG-1
+	andi t1, a3, ~(SZREG-1)
+	andi t0, t0, ~(SZREG-1)
+	/*
+	 * a3: terminal address of target region
+	 * t0: lowest doubleword-aligned address in target region
+	 * t1: highest doubleword-aligned address in target region
+	 */
+	bgeu t0, t1, 2f
+	bltu a0, t0, 4f
+1:
+	fixup REG_S, zero, (a0), 10f
+	addi a0, a0, SZREG
+	bltu a0, t1, 1b
+2:
+	bltu a0, a3, 5f
+
+3:
+	/* Disable access to user memory */
+	csrc sstatus, t6
+	li a0, 0
+	ret
+4: /* Edge case: unalignment */
+	fixup sb, zero, (a0), 10f
+	addi a0, a0, 1
+	bltu a0, t0, 4b
+	j 1b
+5: /* Edge case: remainder */
+	fixup sb, zero, (a0), 10f
+	addi a0, a0, 1
+	bltu a0, a3, 5b
+	j 3b
+ENDPROC(__clear_user)
+
+	.section .fixup,"ax"
+	.balign 4
+10:
+	/* Disable access to user memory */
+	csrs sstatus, t6
+	sub a0, a3, a0
+	ret
+	.previous