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Diffstat (limited to 'arch/nios2/kernel/insnemu.S')
| -rw-r--r-- | arch/nios2/kernel/insnemu.S | 580 |
1 files changed, 580 insertions, 0 deletions
diff --git a/arch/nios2/kernel/insnemu.S b/arch/nios2/kernel/insnemu.S new file mode 100644 index 000000000..a027cc68b --- /dev/null +++ b/arch/nios2/kernel/insnemu.S @@ -0,0 +1,580 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * Copyright (C) 2003-2013 Altera Corporation + * All rights reserved. + */ + + +#include <linux/linkage.h> +#include <asm/entry.h> + +.set noat +.set nobreak + +/* +* Explicitly allow the use of r1 (the assembler temporary register) +* within this code. This register is normally reserved for the use of +* the compiler. +*/ + +ENTRY(instruction_trap) + ldw r1, PT_R1(sp) // Restore registers + ldw r2, PT_R2(sp) + ldw r3, PT_R3(sp) + ldw r4, PT_R4(sp) + ldw r5, PT_R5(sp) + ldw r6, PT_R6(sp) + ldw r7, PT_R7(sp) + ldw r8, PT_R8(sp) + ldw r9, PT_R9(sp) + ldw r10, PT_R10(sp) + ldw r11, PT_R11(sp) + ldw r12, PT_R12(sp) + ldw r13, PT_R13(sp) + ldw r14, PT_R14(sp) + ldw r15, PT_R15(sp) + ldw ra, PT_RA(sp) + ldw fp, PT_FP(sp) + ldw gp, PT_GP(sp) + ldw et, PT_ESTATUS(sp) + wrctl estatus, et + ldw ea, PT_EA(sp) + ldw et, PT_SP(sp) /* backup sp in et */ + + addi sp, sp, PT_REGS_SIZE + + /* INSTRUCTION EMULATION + * --------------------- + * + * Nios II processors generate exceptions for unimplemented instructions. + * The routines below emulate these instructions. Depending on the + * processor core, the only instructions that might need to be emulated + * are div, divu, mul, muli, mulxss, mulxsu, and mulxuu. + * + * The emulations match the instructions, except for the following + * limitations: + * + * 1) The emulation routines do not emulate the use of the exception + * temporary register (et) as a source operand because the exception + * handler already has modified it. + * + * 2) The routines do not emulate the use of the stack pointer (sp) or + * the exception return address register (ea) as a destination because + * modifying these registers crashes the exception handler or the + * interrupted routine. + * + * Detailed Design + * --------------- + * + * The emulation routines expect the contents of integer registers r0-r31 + * to be on the stack at addresses sp, 4(sp), 8(sp), ... 124(sp). The + * routines retrieve source operands from the stack and modify the + * destination register's value on the stack prior to the end of the + * exception handler. Then all registers except the destination register + * are restored to their previous values. + * + * The instruction that causes the exception is found at address -4(ea). + * The instruction's OP and OPX fields identify the operation to be + * performed. + * + * One instruction, muli, is an I-type instruction that is identified by + * an OP field of 0x24. + * + * muli AAAAA,BBBBB,IIIIIIIIIIIIIIII,-0x24- + * 27 22 6 0 <-- LSB of field + * + * The remaining emulated instructions are R-type and have an OP field + * of 0x3a. Their OPX fields identify them. + * + * R-type AAAAA,BBBBB,CCCCC,XXXXXX,NNNNN,-0x3a- + * 27 22 17 11 6 0 <-- LSB of field + * + * + * Opcode Encoding. muli is identified by its OP value. Then OPX & 0x02 + * is used to differentiate between the division opcodes and the + * remaining multiplication opcodes. + * + * Instruction OP OPX OPX & 0x02 + * ----------- ---- ---- ---------- + * muli 0x24 + * divu 0x3a 0x24 0 + * div 0x3a 0x25 0 + * mul 0x3a 0x27 != 0 + * mulxuu 0x3a 0x07 != 0 + * mulxsu 0x3a 0x17 != 0 + * mulxss 0x3a 0x1f != 0 + */ + + + /* + * Save everything on the stack to make it easy for the emulation + * routines to retrieve the source register operands. + */ + + addi sp, sp, -128 + stw zero, 0(sp) /* Save zero on stack to avoid special case for r0. */ + stw r1, 4(sp) + stw r2, 8(sp) + stw r3, 12(sp) + stw r4, 16(sp) + stw r5, 20(sp) + stw r6, 24(sp) + stw r7, 28(sp) + stw r8, 32(sp) + stw r9, 36(sp) + stw r10, 40(sp) + stw r11, 44(sp) + stw r12, 48(sp) + stw r13, 52(sp) + stw r14, 56(sp) + stw r15, 60(sp) + stw r16, 64(sp) + stw r17, 68(sp) + stw r18, 72(sp) + stw r19, 76(sp) + stw r20, 80(sp) + stw r21, 84(sp) + stw r22, 88(sp) + stw r23, 92(sp) + /* Don't bother to save et. It's already been changed. */ + rdctl r5, estatus + stw r5, 100(sp) + + stw gp, 104(sp) + stw et, 108(sp) /* et contains previous sp value. */ + stw fp, 112(sp) + stw ea, 116(sp) + stw ra, 120(sp) + + + /* + * Split the instruction into its fields. We need 4*A, 4*B, and 4*C as + * offsets to the stack pointer for access to the stored register values. + */ + ldw r2,-4(ea) /* r2 = AAAAA,BBBBB,IIIIIIIIIIIIIIII,PPPPPP */ + roli r3, r2, 7 /* r3 = BBB,IIIIIIIIIIIIIIII,PPPPPP,AAAAA,BB */ + roli r4, r3, 3 /* r4 = IIIIIIIIIIIIIIII,PPPPPP,AAAAA,BBBBB */ + roli r5, r4, 2 /* r5 = IIIIIIIIIIIIII,PPPPPP,AAAAA,BBBBB,II */ + srai r4, r4, 16 /* r4 = (sign-extended) IMM16 */ + roli r6, r5, 5 /* r6 = XXXX,NNNNN,PPPPPP,AAAAA,BBBBB,CCCCC,XX */ + andi r2, r2, 0x3f /* r2 = 00000000000000000000000000,PPPPPP */ + andi r3, r3, 0x7c /* r3 = 0000000000000000000000000,AAAAA,00 */ + andi r5, r5, 0x7c /* r5 = 0000000000000000000000000,BBBBB,00 */ + andi r6, r6, 0x7c /* r6 = 0000000000000000000000000,CCCCC,00 */ + + /* Now + * r2 = OP + * r3 = 4*A + * r4 = IMM16 (sign extended) + * r5 = 4*B + * r6 = 4*C + */ + + /* + * Get the operands. + * + * It is necessary to check for muli because it uses an I-type + * instruction format, while the other instructions are have an R-type + * format. + * + * Prepare for either multiplication or division loop. + * They both loop 32 times. + */ + movi r14, 32 + + add r3, r3, sp /* r3 = address of A-operand. */ + ldw r3, 0(r3) /* r3 = A-operand. */ + movi r7, 0x24 /* muli opcode (I-type instruction format) */ + beq r2, r7, mul_immed /* muli doesn't use the B register as a source */ + + add r5, r5, sp /* r5 = address of B-operand. */ + ldw r5, 0(r5) /* r5 = B-operand. */ + /* r4 = SSSSSSSSSSSSSSSS,-----IMM16------ */ + /* IMM16 not needed, align OPX portion */ + /* r4 = SSSSSSSSSSSSSSSS,CCCCC,-OPX--,00000 */ + srli r4, r4, 5 /* r4 = 00000,SSSSSSSSSSSSSSSS,CCCCC,-OPX-- */ + andi r4, r4, 0x3f /* r4 = 00000000000000000000000000,-OPX-- */ + + /* Now + * r2 = OP + * r3 = src1 + * r5 = src2 + * r4 = OPX (no longer can be muli) + * r6 = 4*C + */ + + + /* + * Multiply or Divide? + */ + andi r7, r4, 0x02 /* For R-type multiply instructions, + OPX & 0x02 != 0 */ + bne r7, zero, multiply + + + /* DIVISION + * + * Divide an unsigned dividend by an unsigned divisor using + * a shift-and-subtract algorithm. The example below shows + * 43 div 7 = 6 for 8-bit integers. This classic algorithm uses a + * single register to store both the dividend and the quotient, + * allowing both values to be shifted with a single instruction. + * + * remainder dividend:quotient + * --------- ----------------- + * initialize 00000000 00101011: + * shift 00000000 0101011:_ + * remainder >= divisor? no 00000000 0101011:0 + * shift 00000000 101011:0_ + * remainder >= divisor? no 00000000 101011:00 + * shift 00000001 01011:00_ + * remainder >= divisor? no 00000001 01011:000 + * shift 00000010 1011:000_ + * remainder >= divisor? no 00000010 1011:0000 + * shift 00000101 011:0000_ + * remainder >= divisor? no 00000101 011:00000 + * shift 00001010 11:00000_ + * remainder >= divisor? yes 00001010 11:000001 + * remainder -= divisor - 00000111 + * ---------- + * 00000011 11:000001 + * shift 00000111 1:000001_ + * remainder >= divisor? yes 00000111 1:0000011 + * remainder -= divisor - 00000111 + * ---------- + * 00000000 1:0000011 + * shift 00000001 :0000011_ + * remainder >= divisor? no 00000001 :00000110 + * + * The quotient is 00000110. + */ + +divide: + /* + * Prepare for division by assuming the result + * is unsigned, and storing its "sign" as 0. + */ + movi r17, 0 + + + /* Which division opcode? */ + xori r7, r4, 0x25 /* OPX of div */ + bne r7, zero, unsigned_division + + + /* + * OPX is div. Determine and store the sign of the quotient. + * Then take the absolute value of both operands. + */ + xor r17, r3, r5 /* MSB contains sign of quotient */ + bge r3,zero,dividend_is_nonnegative + sub r3, zero, r3 /* -r3 */ +dividend_is_nonnegative: + bge r5, zero, divisor_is_nonnegative + sub r5, zero, r5 /* -r5 */ +divisor_is_nonnegative: + + +unsigned_division: + /* Initialize the unsigned-division loop. */ + movi r13, 0 /* remainder = 0 */ + + /* Now + * r3 = dividend : quotient + * r4 = 0x25 for div, 0x24 for divu + * r5 = divisor + * r13 = remainder + * r14 = loop counter (already initialized to 32) + * r17 = MSB contains sign of quotient + */ + + + /* + * for (count = 32; count > 0; --count) + * { + */ +divide_loop: + + /* + * Division: + * + * (remainder:dividend:quotient) <<= 1; + */ + slli r13, r13, 1 + cmplt r7, r3, zero /* r7 = MSB of r3 */ + or r13, r13, r7 + slli r3, r3, 1 + + + /* + * if (remainder >= divisor) + * { + * set LSB of quotient + * remainder -= divisor; + * } + */ + bltu r13, r5, div_skip + ori r3, r3, 1 + sub r13, r13, r5 +div_skip: + + /* + * } + */ + subi r14, r14, 1 + bne r14, zero, divide_loop + + + /* Now + * r3 = quotient + * r4 = 0x25 for div, 0x24 for divu + * r6 = 4*C + * r17 = MSB contains sign of quotient + */ + + + /* + * Conditionally negate signed quotient. If quotient is unsigned, + * the sign already is initialized to 0. + */ + bge r17, zero, quotient_is_nonnegative + sub r3, zero, r3 /* -r3 */ + quotient_is_nonnegative: + + + /* + * Final quotient is in r3. + */ + add r6, r6, sp + stw r3, 0(r6) /* write quotient to stack */ + br restore_registers + + + + + /* MULTIPLICATION + * + * A "product" is the number that one gets by summing a "multiplicand" + * several times. The "multiplier" specifies the number of copies of the + * multiplicand that are summed. + * + * Actual multiplication algorithms don't use repeated addition, however. + * Shift-and-add algorithms get the same answer as repeated addition, and + * they are faster. To compute the lower half of a product (pppp below) + * one shifts the product left before adding in each of the partial + * products (a * mmmm) through (d * mmmm). + * + * To compute the upper half of a product (PPPP below), one adds in the + * partial products (d * mmmm) through (a * mmmm), each time following + * the add by a right shift of the product. + * + * mmmm + * * abcd + * ------ + * #### = d * mmmm + * #### = c * mmmm + * #### = b * mmmm + * #### = a * mmmm + * -------- + * PPPPpppp + * + * The example above shows 4 partial products. Computing actual Nios II + * products requires 32 partials. + * + * It is possible to compute the result of mulxsu from the result of + * mulxuu because the only difference between the results of these two + * opcodes is the value of the partial product associated with the sign + * bit of rA. + * + * mulxsu = mulxuu - (rA < 0) ? rB : 0; + * + * It is possible to compute the result of mulxss from the result of + * mulxsu because the only difference between the results of these two + * opcodes is the value of the partial product associated with the sign + * bit of rB. + * + * mulxss = mulxsu - (rB < 0) ? rA : 0; + * + */ + +mul_immed: + /* Opcode is muli. Change it into mul for remainder of algorithm. */ + mov r6, r5 /* Field B is dest register, not field C. */ + mov r5, r4 /* Field IMM16 is src2, not field B. */ + movi r4, 0x27 /* OPX of mul is 0x27 */ + +multiply: + /* Initialize the multiplication loop. */ + movi r9, 0 /* mul_product = 0 */ + movi r10, 0 /* mulxuu_product = 0 */ + mov r11, r5 /* save original multiplier for mulxsu and mulxss */ + mov r12, r5 /* mulxuu_multiplier (will be shifted) */ + movi r16, 1 /* used to create "rori B,A,1" from "ror B,A,r16" */ + + /* Now + * r3 = multiplicand + * r5 = mul_multiplier + * r6 = 4 * dest_register (used later as offset to sp) + * r7 = temp + * r9 = mul_product + * r10 = mulxuu_product + * r11 = original multiplier + * r12 = mulxuu_multiplier + * r14 = loop counter (already initialized) + * r16 = 1 + */ + + + /* + * for (count = 32; count > 0; --count) + * { + */ +multiply_loop: + + /* + * mul_product <<= 1; + * lsb = multiplier & 1; + */ + slli r9, r9, 1 + andi r7, r12, 1 + + /* + * if (lsb == 1) + * { + * mulxuu_product += multiplicand; + * } + */ + beq r7, zero, mulx_skip + add r10, r10, r3 + cmpltu r7, r10, r3 /* Save the carry from the MSB of mulxuu_product. */ + ror r7, r7, r16 /* r7 = 0x80000000 on carry, or else 0x00000000 */ +mulx_skip: + + /* + * if (MSB of mul_multiplier == 1) + * { + * mul_product += multiplicand; + * } + */ + bge r5, zero, mul_skip + add r9, r9, r3 +mul_skip: + + /* + * mulxuu_product >>= 1; logical shift + * mul_multiplier <<= 1; done with MSB + * mulx_multiplier >>= 1; done with LSB + */ + srli r10, r10, 1 + or r10, r10, r7 /* OR in the saved carry bit. */ + slli r5, r5, 1 + srli r12, r12, 1 + + + /* + * } + */ + subi r14, r14, 1 + bne r14, zero, multiply_loop + + + /* + * Multiply emulation loop done. + */ + + /* Now + * r3 = multiplicand + * r4 = OPX + * r6 = 4 * dest_register (used later as offset to sp) + * r7 = temp + * r9 = mul_product + * r10 = mulxuu_product + * r11 = original multiplier + */ + + + /* Calculate address for result from 4 * dest_register */ + add r6, r6, sp + + + /* + * Select/compute the result based on OPX. + */ + + + /* OPX == mul? Then store. */ + xori r7, r4, 0x27 + beq r7, zero, store_product + + /* It's one of the mulx.. opcodes. Move over the result. */ + mov r9, r10 + + /* OPX == mulxuu? Then store. */ + xori r7, r4, 0x07 + beq r7, zero, store_product + + /* Compute mulxsu + * + * mulxsu = mulxuu - (rA < 0) ? rB : 0; + */ + bge r3, zero, mulxsu_skip + sub r9, r9, r11 +mulxsu_skip: + + /* OPX == mulxsu? Then store. */ + xori r7, r4, 0x17 + beq r7, zero, store_product + + /* Compute mulxss + * + * mulxss = mulxsu - (rB < 0) ? rA : 0; + */ + bge r11,zero,mulxss_skip + sub r9, r9, r3 +mulxss_skip: + /* At this point, assume that OPX is mulxss, so store*/ + + +store_product: + stw r9, 0(r6) + + +restore_registers: + /* No need to restore r0. */ + ldw r5, 100(sp) + wrctl estatus, r5 + + ldw r1, 4(sp) + ldw r2, 8(sp) + ldw r3, 12(sp) + ldw r4, 16(sp) + ldw r5, 20(sp) + ldw r6, 24(sp) + ldw r7, 28(sp) + ldw r8, 32(sp) + ldw r9, 36(sp) + ldw r10, 40(sp) + ldw r11, 44(sp) + ldw r12, 48(sp) + ldw r13, 52(sp) + ldw r14, 56(sp) + ldw r15, 60(sp) + ldw r16, 64(sp) + ldw r17, 68(sp) + ldw r18, 72(sp) + ldw r19, 76(sp) + ldw r20, 80(sp) + ldw r21, 84(sp) + ldw r22, 88(sp) + ldw r23, 92(sp) + /* Does not need to restore et */ + ldw gp, 104(sp) + + ldw fp, 112(sp) + ldw ea, 116(sp) + ldw ra, 120(sp) + ldw sp, 108(sp) /* last restore sp */ + eret + +.set at +.set break |