xref: /linux/arch/arc/net/bpf_jit_arcv2.c (revision 42a19aa1707cce382bc5e534e2e36024c3611674)

// SPDX-License-Identifier: GPL-2.0
/*
 * The ARCv2 backend of Just-In-Time compiler for eBPF bytecode.
 *
 * Copyright (c) 2024 Synopsys Inc.
 * Author: Shahab Vahedi <shahab@synopsys.com>
 */
#include <linux/bug.h>
#include "bpf_jit.h"

/* ARC core registers. */
enum {
	ARC_R_0,  ARC_R_1,  ARC_R_2,  ARC_R_3,  ARC_R_4,  ARC_R_5,
	ARC_R_6,  ARC_R_7,  ARC_R_8,  ARC_R_9,  ARC_R_10, ARC_R_11,
	ARC_R_12, ARC_R_13, ARC_R_14, ARC_R_15, ARC_R_16, ARC_R_17,
	ARC_R_18, ARC_R_19, ARC_R_20, ARC_R_21, ARC_R_22, ARC_R_23,
	ARC_R_24, ARC_R_25, ARC_R_26, ARC_R_FP, ARC_R_SP, ARC_R_ILINK,
	ARC_R_30, ARC_R_BLINK,
	/*
	 * Having ARC_R_IMM encoded as source register means there is an
	 * immediate that must be interpreted from the next 4 bytes. If
	 * encoded as the destination register though, it implies that the
	 * output of the operation is not assigned to any register. The
	 * latter is helpful if we only care about updating the CPU status
	 * flags.
	 */
	ARC_R_IMM = 62
};

/*
 * Remarks about the rationale behind the chosen mapping:
 *
 * - BPF_REG_{1,2,3,4} are the argument registers and must be mapped to
 *   argument registers in ARCv2 ABI: r0-r7. The r7 registers is the last
 *   argument register in the ABI. Therefore BPF_REG_5, as the fifth
 *   argument, must be pushed onto the stack. This is a must for calling
 *   in-kernel functions.
 *
 * - In ARCv2 ABI, the return value is in r0 for 32-bit results and (r1,r0)
 *   for 64-bit results. However, because they're already used for BPF_REG_1,
 *   the next available scratch registers, r8 and r9, are the best candidates
 *   for BPF_REG_0. After a "call" to a(n) (in-kernel) function, the result
 *   is "mov"ed to these registers. At a BPF_EXIT, their value is "mov"ed to
 *   (r1,r0).
 *   It is worth mentioning that scratch registers are the best choice for
 *   BPF_REG_0, because it is very popular in BPF instruction encoding.
 *
 * - JIT_REG_TMP is an artifact needed to translate some BPF instructions.
 *   Its life span is one single BPF instruction. Since during the
 *   analyze_reg_usage(), it is not known if temporary registers are used,
 *   it is mapped to ARC's scratch registers: r10 and r11. Therefore, they
 *   don't matter in analysing phase and don't need saving. This temporary
 *   register is added as yet another index in the bpf2arc array, so it will
 *   unfold like the rest of registers during the code generation process.
 *
 * - Mapping of callee-saved BPF registers, BPF_REG_{6,7,8,9}, starts from
 *   (r15,r14) register pair. The (r13,r12) is not a good choice, because
 *   in ARCv2 ABI, r12 is not a callee-saved register and this can cause
 *   problem when calling an in-kernel function. Theoretically, the mapping
 *   could start from (r14,r13), but it is not a conventional ARCv2 register
 *   pair. To have a future proof design, I opted for this arrangement.
 *   If/when we decide to add ARCv2 instructions that do use register pairs,
 *   the mapping, hopefully, doesn't need to be revisited.
 */
static const u8 bpf2arc[][2] = {
	/* Return value from in-kernel function, and exit value from eBPF */
	[BPF_REG_0] = {ARC_R_8, ARC_R_9},
	/* Arguments from eBPF program to in-kernel function */
	[BPF_REG_1] = {ARC_R_0, ARC_R_1},
	[BPF_REG_2] = {ARC_R_2, ARC_R_3},
	[BPF_REG_3] = {ARC_R_4, ARC_R_5},
	[BPF_REG_4] = {ARC_R_6, ARC_R_7},
	/* Remaining arguments, to be passed on the stack per 32-bit ABI */
	[BPF_REG_5] = {ARC_R_22, ARC_R_23},
	/* Callee-saved registers that in-kernel function will preserve */
	[BPF_REG_6] = {ARC_R_14, ARC_R_15},
	[BPF_REG_7] = {ARC_R_16, ARC_R_17},
	[BPF_REG_8] = {ARC_R_18, ARC_R_19},
	[BPF_REG_9] = {ARC_R_20, ARC_R_21},
	/* Read-only frame pointer to access the eBPF stack. 32-bit only. */
	[BPF_REG_FP] = {ARC_R_FP, },
	/* Register for blinding constants */
	[BPF_REG_AX] = {ARC_R_24, ARC_R_25},
	/* Temporary registers for internal use */
	[JIT_REG_TMP] = {ARC_R_10, ARC_R_11}
};

#define ARC_CALLEE_SAVED_REG_FIRST ARC_R_13
#define ARC_CALLEE_SAVED_REG_LAST  ARC_R_25

#define REG_LO(r) (bpf2arc[(r)][0])
#define REG_HI(r) (bpf2arc[(r)][1])

/*
 * To comply with ARCv2 ABI, BPF's arg5 must be put on stack. After which,
 * the stack needs to be restored by ARG5_SIZE.
 */
#define ARG5_SIZE 8

/* Instruction lengths in bytes. */
enum {
	INSN_len_normal = 4,	/* Normal instructions length. */
	INSN_len_imm = 4	/* Length of an extra 32-bit immediate. */
};

/* ZZ defines the size of operation in encodings that it is used. */
enum {
	ZZ_1_byte = 1,
	ZZ_2_byte = 2,
	ZZ_4_byte = 0,
	ZZ_8_byte = 3
};

/*
 * AA is mostly about address write back mode. It determines if the
 * address in question should be updated before usage or after:
 *   addr += offset; data = *addr;
 *   data = *addr; addr += offset;
 *
 * In "scaling" mode, the effective address will become the sum
 * of "address" + "index"*"size". The "size" is specified by the
 * "ZZ" field. There is no write back when AA is set for scaling:
 *   data = *(addr + offset<<zz)
 */
enum {
	AA_none  = 0,
	AA_pre   = 1,	/* in assembly known as "a/aw". */
	AA_post  = 2,	/* in assembly known as "ab". */
	AA_scale = 3	/* in assembly known as "as". */
};

/* X flag determines the mode of extension. */
enum {
	X_zero = 0,
	X_sign = 1
};

/* Condition codes. */
enum {
	CC_always     = 0,	/* condition is true all the time */
	CC_equal      = 1,	/* if status32.z flag is set */
	CC_unequal    = 2,	/* if status32.z flag is clear */
	CC_positive   = 3,	/* if status32.n flag is clear */
	CC_negative   = 4,	/* if status32.n flag is set */
	CC_less_u     = 5,	/* less than (unsigned) */
	CC_less_eq_u  = 14,	/* less than or equal (unsigned) */
	CC_great_eq_u = 6,	/* greater than or equal (unsigned) */
	CC_great_u    = 13,	/* greater than (unsigned) */
	CC_less_s     = 11,	/* less than (signed) */
	CC_less_eq_s  = 12,	/* less than or equal (signed) */
	CC_great_eq_s = 10,	/* greater than or equal (signed) */
	CC_great_s    = 9	/* greater than (signed) */
};

#define IN_U6_RANGE(x)	((x) <= (0x40      - 1) && (x) >= 0)
#define IN_S9_RANGE(x)	((x) <= (0x100     - 1) && (x) >= -0x100)
#define IN_S12_RANGE(x)	((x) <= (0x800     - 1) && (x) >= -0x800)
#define IN_S21_RANGE(x)	((x) <= (0x100000  - 1) && (x) >= -0x100000)
#define IN_S25_RANGE(x)	((x) <= (0x1000000 - 1) && (x) >= -0x1000000)

/* Operands in most of the encodings. */
#define OP_A(x)	((x) & 0x03f)
#define OP_B(x)	((((x) & 0x07) << 24) | (((x) & 0x38) <<  9))
#define OP_C(x)	(((x) & 0x03f) << 6)
#define OP_IMM	(OP_C(ARC_R_IMM))
#define COND(x)	(OP_A((x) & 31))
#define FLAG(x)	(((x) & 1) << 15)

/*
 * The 4-byte encoding of "mov b,c":
 *
 * 0010_0bbb 0000_1010 0BBB_cccc cc00_0000
 *
 * b:  BBBbbb		destination register
 * c:  cccccc		source register
 */
#define OPC_MOV		0x200a0000

/*
 * The 4-byte encoding of "mov b,s12" (used for moving small immediates):
 *
 * 0010_0bbb 1000_1010 0BBB_ssss ssSS_SSSS
 *
 * b:  BBBbbb		destination register
 * s:  SSSSSSssssss	source immediate (signed)
 */
#define OPC_MOVI	0x208a0000
#define MOVI_S12(x)	((((x) & 0xfc0) >> 6) | (((x) & 0x3f) << 6))

/*
 * The 4-byte encoding of "mov[.qq] b,u6", used for conditional
 * moving of even smaller immediates:
 *
 * 0010_0bbb 1100_1010 0BBB_cccc cciq_qqqq
 *
 * qq: qqqqq		condition code
 * i:			If set, c is considered a 6-bit immediate, else a reg.
 *
 * b:  BBBbbb		destination register
 * c:  cccccc		source
 */
#define OPC_MOV_CC	0x20ca0000
#define MOV_CC_I	BIT(5)
#define OPC_MOVU_CC	(OPC_MOV_CC | MOV_CC_I)

/*
 * The 4-byte encoding of "sexb b,c" (8-bit sign extension):
 *
 * 0010_0bbb 0010_1111 0BBB_cccc cc00_0101
 *
 * b:  BBBbbb		destination register
 * c:  cccccc		source register
 */
#define OPC_SEXB	0x202f0005

/*
 * The 4-byte encoding of "sexh b,c" (16-bit sign extension):
 *
 * 0010_0bbb 0010_1111 0BBB_cccc cc00_0110
 *
 * b:  BBBbbb		destination register
 * c:  cccccc		source register
 */
#define OPC_SEXH	0x202f0006

/*
 * The 4-byte encoding of "ld[zz][.x][.aa] c,[b,s9]":
 *
 * 0001_0bbb ssss_ssss SBBB_0aaz zxcc_cccc
 *
 * zz:			size mode
 * aa:			address write back mode
 * x:			extension mode
 *
 * s9: S_ssss_ssss	9-bit signed number
 * b:  BBBbbb		source reg for address
 * c:  cccccc		destination register
 */
#define OPC_LOAD	0x10000000
#define LOAD_X(x)	((x) << 6)
#define LOAD_ZZ(x)	((x) << 7)
#define LOAD_AA(x)	((x) << 9)
#define LOAD_S9(x)	((((x) & 0x0ff) << 16) | (((x) & 0x100) <<  7))
#define LOAD_C(x)	((x) & 0x03f)
/* Unsigned and signed loads. */
#define OPC_LDU		(OPC_LOAD | LOAD_X(X_zero))
#define OPC_LDS		(OPC_LOAD | LOAD_X(X_sign))
/* 32-bit load. */
#define OPC_LD32	(OPC_LDU | LOAD_ZZ(ZZ_4_byte))
/* "pop reg" is merely a "ld.ab reg,[sp,4]". */
#define OPC_POP		\
	(OPC_LD32 | LOAD_AA(AA_post) | LOAD_S9(4) | OP_B(ARC_R_SP))

/*
 * The 4-byte encoding of "st[zz][.aa] c,[b,s9]":
 *
 * 0001_1bbb ssss_ssss SBBB_cccc cc0a_azz0
 *
 * zz: zz		size mode
 * aa: aa		address write back mode
 *
 * s9: S_ssss_ssss	9-bit signed number
 * b:  BBBbbb		source reg for address
 * c:  cccccc		source reg to be stored
 */
#define OPC_STORE	0x18000000
#define STORE_ZZ(x)	((x) << 1)
#define STORE_AA(x)	((x) << 3)
#define STORE_S9(x)	((((x) & 0x0ff) << 16) | (((x) & 0x100) <<  7))
/* 32-bit store. */
#define OPC_ST32	(OPC_STORE | STORE_ZZ(ZZ_4_byte))
/* "push reg" is merely a "st.aw reg,[sp,-4]". */
#define OPC_PUSH	\
	(OPC_ST32 | STORE_AA(AA_pre) | STORE_S9(-4) | OP_B(ARC_R_SP))

/*
 * The 4-byte encoding of "add a,b,c":
 *
 * 0010_0bbb 0i00_0000 fBBB_cccc ccaa_aaaa
 *
 * f:                   indicates if flags (carry, etc.) should be updated
 * i:			If set, c is considered a 6-bit immediate, else a reg.
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_ADD		0x20000000
/* Addition with updating the pertinent flags in "status32" register. */
#define OPC_ADDF	(OPC_ADD | FLAG(1))
#define ADDI		BIT(22)
#define ADDI_U6(x)	OP_C(x)
#define OPC_ADDI	(OPC_ADD | ADDI)
#define OPC_ADDIF	(OPC_ADDI | FLAG(1))
#define OPC_ADD_I	(OPC_ADD | OP_IMM)

/*
 * The 4-byte encoding of "adc a,b,c" (addition with carry):
 *
 * 0010_0bbb 0i00_0001 0BBB_cccc ccaa_aaaa
 *
 * i:			if set, c is considered a 6-bit immediate, else a reg.
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_ADC		0x20010000
#define ADCI		BIT(22)
#define ADCI_U6(x)	OP_C(x)
#define OPC_ADCI	(OPC_ADC | ADCI)

/*
 * The 4-byte encoding of "sub a,b,c":
 *
 * 0010_0bbb 0i00_0010 fBBB_cccc ccaa_aaaa
 *
 * f:                   indicates if flags (carry, etc.) should be updated
 * i:			if set, c is considered a 6-bit immediate, else a reg.
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_SUB		0x20020000
/* Subtraction with updating the pertinent flags in "status32" register. */
#define OPC_SUBF	(OPC_SUB | FLAG(1))
#define SUBI		BIT(22)
#define SUBI_U6(x)	OP_C(x)
#define OPC_SUBI	(OPC_SUB | SUBI)
#define OPC_SUB_I	(OPC_SUB | OP_IMM)

/*
 * The 4-byte encoding of "sbc a,b,c" (subtraction with carry):
 *
 * 0010_0bbb 0000_0011 fBBB_cccc ccaa_aaaa
 *
 * f:                   indicates if flags (carry, etc.) should be updated
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_SBC		0x20030000

/*
 * The 4-byte encoding of "cmp[.qq] b,c":
 *
 * 0010_0bbb 1100_1100 1BBB_cccc cc0q_qqqq
 *
 * qq:	qqqqq		condition code
 *
 * b:  BBBbbb		the 1st operand
 * c:  cccccc		the 2nd operand
 */
#define OPC_CMP		0x20cc8000

/*
 * The 4-byte encoding of "neg a,b":
 *
 * 0010_0bbb 0100_1110 0BBB_0000 00aa_aaaa
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		input
 */
#define OPC_NEG		0x204e0000

/*
 * The 4-byte encoding of "mpy a,b,c".
 * mpy is the signed 32-bit multiplication with the lower 32-bit
 * of the product as the result.
 *
 * 0010_0bbb 0001_1010 0BBB_cccc ccaa_aaaa
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_MPY		0x201a0000
#define OPC_MPYI	(OPC_MPY | OP_IMM)

/*
 * The 4-byte encoding of "mpydu a,b,c".
 * mpydu is the unsigned 32-bit multiplication with the lower 32-bit of
 * the product in register "a" and the higher 32-bit in register "a+1".
 *
 * 0010_1bbb 0001_1001 0BBB_cccc ccaa_aaaa
 *
 * a:  aaaaaa		64-bit result in registers (R_a+1,R_a)
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_MPYDU	0x28190000
#define OPC_MPYDUI	(OPC_MPYDU | OP_IMM)

/*
 * The 4-byte encoding of "divu a,b,c" (unsigned division):
 *
 * 0010_1bbb 0000_0101 0BBB_cccc ccaa_aaaa
 *
 * a:  aaaaaa		result (quotient)
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand (divisor)
 */
#define OPC_DIVU	0x28050000
#define OPC_DIVUI	(OPC_DIVU | OP_IMM)

/*
 * The 4-byte encoding of "div a,b,c" (signed division):
 *
 * 0010_1bbb 0000_0100 0BBB_cccc ccaa_aaaa
 *
 * a:  aaaaaa		result (quotient)
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand (divisor)
 */
#define OPC_DIVS	0x28040000
#define OPC_DIVSI	(OPC_DIVS | OP_IMM)

/*
 * The 4-byte encoding of "remu a,b,c" (unsigned remainder):
 *
 * 0010_1bbb 0000_1001 0BBB_cccc ccaa_aaaa
 *
 * a:  aaaaaa		result (remainder)
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand (divisor)
 */
#define OPC_REMU	0x28090000
#define OPC_REMUI	(OPC_REMU | OP_IMM)

/*
 * The 4-byte encoding of "rem a,b,c" (signed remainder):
 *
 * 0010_1bbb 0000_1000 0BBB_cccc ccaa_aaaa
 *
 * a:  aaaaaa		result (remainder)
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand (divisor)
 */
#define OPC_REMS	0x28080000
#define OPC_REMSI	(OPC_REMS | OP_IMM)

/*
 * The 4-byte encoding of "and a,b,c":
 *
 * 0010_0bbb 0000_0100 fBBB_cccc ccaa_aaaa
 *
 * f:                   indicates if zero and negative flags should be updated
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_AND		0x20040000
#define OPC_ANDI	(OPC_AND | OP_IMM)

/*
 * The 4-byte encoding of "tst[.qq] b,c".
 * Checks if the two input operands have any bit set at the same
 * position.
 *
 * 0010_0bbb 1100_1011 1BBB_cccc cc0q_qqqq
 *
 * qq:	qqqqq		condition code
 *
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_TST		0x20cb8000

/*
 * The 4-byte encoding of "or a,b,c":
 *
 * 0010_0bbb 0000_0101 0BBB_cccc ccaa_aaaa
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_OR		0x20050000
#define OPC_ORI		(OPC_OR | OP_IMM)

/*
 * The 4-byte encoding of "xor a,b,c":
 *
 * 0010_0bbb 0000_0111 0BBB_cccc ccaa_aaaa
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		the 1st input operand
 * c:  cccccc		the 2nd input operand
 */
#define OPC_XOR		0x20070000
#define OPC_XORI	(OPC_XOR | OP_IMM)

/*
 * The 4-byte encoding of "not b,c":
 *
 * 0010_0bbb 0010_1111 0BBB_cccc cc00_1010
 *
 * b:  BBBbbb		result
 * c:  cccccc		input
 */
#define OPC_NOT		0x202f000a

/*
 * The 4-byte encoding of "btst b,u6":
 *
 * 0010_0bbb 0101_0001 1BBB_uuuu uu00_0000
 *
 * b:  BBBbbb		input number to check
 * u6: uuuuuu		6-bit unsigned number specifying bit position to check
 */
#define OPC_BTSTU6	0x20518000
#define BTST_U6(x)	(OP_C((x) & 63))

/*
 * The 4-byte encoding of "asl[.qq] b,b,c" (arithmetic shift left):
 *
 * 0010_1bbb 0i00_0000 0BBB_cccc ccaa_aaaa
 *
 * i:			if set, c is considered a 5-bit immediate, else a reg.
 *
 * b:  BBBbbb		result and the first operand (number to be shifted)
 * c:  cccccc		amount to be shifted
 */
#define OPC_ASL		0x28000000
#define ASL_I		BIT(22)
#define ASLI_U6(x)	OP_C((x) & 31)
#define OPC_ASLI	(OPC_ASL | ASL_I)

/*
 * The 4-byte encoding of "asr a,b,c" (arithmetic shift right):
 *
 * 0010_1bbb 0i00_0010 0BBB_cccc ccaa_aaaa
 *
 * i:			if set, c is considered a 6-bit immediate, else a reg.
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		first input:  number to be shifted
 * c:  cccccc		second input: amount to be shifted
 */
#define OPC_ASR		0x28020000
#define ASR_I		ASL_I
#define ASRI_U6(x)	ASLI_U6(x)
#define OPC_ASRI	(OPC_ASR | ASR_I)

/*
 * The 4-byte encoding of "lsr a,b,c" (logical shift right):
 *
 * 0010_1bbb 0i00_0001 0BBB_cccc ccaa_aaaa
 *
 * i:			if set, c is considered a 6-bit immediate, else a reg.
 *
 * a:  aaaaaa		result
 * b:  BBBbbb		first input:  number to be shifted
 * c:  cccccc		second input: amount to be shifted
 */
#define OPC_LSR		0x28010000
#define LSR_I		ASL_I
#define LSRI_U6(x)	ASLI_U6(x)
#define OPC_LSRI	(OPC_LSR | LSR_I)

/*
 * The 4-byte encoding of "swape b,c":
 *
 * 0010_1bbb 0010_1111 0bbb_cccc cc00_1001
 *
 * b:  BBBbbb		destination register
 * c:  cccccc		source register
 */
#define OPC_SWAPE	0x282f0009

/*
 * Encoding for jump to an address in register:
 * j reg_c
 *
 * 0010_0000 1110_0000 0000_cccc cc00_0000
 *
 * c:  cccccc		register holding the destination address
 */
#define OPC_JMP		0x20e00000
/* Jump to "branch-and-link" register, which effectively is a "return". */
#define OPC_J_BLINK	(OPC_JMP | OP_C(ARC_R_BLINK))

/*
 * Encoding for jump-and-link to an address in register:
 * jl reg_c
 *
 * 0010_0000 0010_0010 0000_cccc cc00_0000
 *
 * c:  cccccc		register holding the destination address
 */
#define OPC_JL		0x20220000

/*
 * Encoding for (conditional) branch to an offset from the current location
 * that is word aligned: (PC & 0xffff_fffc) + s21
 * B[qq] s21
 *
 * 0000_0sss ssss_sss0 SSSS_SSSS SS0q_qqqq
 *
 * qq:	qqqqq				condition code
 * s21:	SSSS SSSS_SSss ssss_ssss	The displacement (21-bit signed)
 *
 * The displacement is supposed to be 16-bit (2-byte) aligned. Therefore,
 * it should be a multiple of 2. Hence, there is an implied '0' bit at its
 * LSB: S_SSSS SSSS_Ssss ssss_sss0
 */
#define OPC_BCC		0x00000000
#define BCC_S21(d)	((((d) & 0x7fe) << 16) | (((d) & 0x1ff800) >> 5))

/*
 * Encoding for unconditional branch to an offset from the current location
 * that is word aligned: (PC & 0xffff_fffc) + s25
 * B s25
 *
 * 0000_0sss ssss_sss1 SSSS_SSSS SS00_TTTT
 *
 * s25:	TTTT SSSS SSSS_SSss ssss_ssss	The displacement (25-bit signed)
 *
 * The displacement is supposed to be 16-bit (2-byte) aligned. Therefore,
 * it should be a multiple of 2. Hence, there is an implied '0' bit at its
 * LSB: T TTTS_SSSS SSSS_Ssss ssss_sss0
 */
#define OPC_B		0x00010000
#define B_S25(d)	((((d) & 0x1e00000) >> 21) | BCC_S21(d))

static inline void emit_2_bytes(u8 *buf, u16 bytes)
{
	*((u16 *)buf) = bytes;
}

static inline void emit_4_bytes(u8 *buf, u32 bytes)
{
	emit_2_bytes(buf, bytes >> 16);
	emit_2_bytes(buf + 2, bytes & 0xffff);
}

static inline u8 bpf_to_arc_size(u8 size)
{
	switch (size) {
	case BPF_B:
		return ZZ_1_byte;
	case BPF_H:
		return ZZ_2_byte;
	case BPF_W:
		return ZZ_4_byte;
	case BPF_DW:
		return ZZ_8_byte;
	default:
		return ZZ_4_byte;
	}
}

/************** Encoders (Deal with ARC regs) ************/

/* Move an immediate to register with a 4-byte instruction. */
static u8 arc_movi_r(u8 *buf, u8 reg, s16 imm)
{
	const u32 insn = OPC_MOVI | OP_B(reg) | MOVI_S12(imm);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* rd <- rs */
static u8 arc_mov_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_MOV | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* The emitted code may have different sizes based on "imm". */
static u8 arc_mov_i(u8 *buf, u8 rd, s32 imm)
{
	const u32 insn = OPC_MOV | OP_B(rd) | OP_IMM;

	if (IN_S12_RANGE(imm))
		return arc_movi_r(buf, rd, imm);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* The emitted code will always have the same size (8). */
static u8 arc_mov_i_fixed(u8 *buf, u8 rd, s32 imm)
{
	const u32 insn = OPC_MOV | OP_B(rd) | OP_IMM;

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* Conditional move. */
static u8 arc_mov_cc_r(u8 *buf, u8 cc, u8 rd, u8 rs)
{
	const u32 insn = OPC_MOV_CC | OP_B(rd) | OP_C(rs) | COND(cc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* Conditional move of a small immediate to rd. */
static u8 arc_movu_cc_r(u8 *buf, u8 cc, u8 rd, u8 imm)
{
	const u32 insn = OPC_MOVU_CC | OP_B(rd) | OP_C(imm) | COND(cc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* Sign extension from a byte. */
static u8 arc_sexb_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_SEXB | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* Sign extension from two bytes. */
static u8 arc_sexh_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_SEXH | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* st reg, [reg_mem, off] */
static u8 arc_st_r(u8 *buf, u8 reg, u8 reg_mem, s16 off, u8 zz)
{
	const u32 insn = OPC_STORE | STORE_ZZ(zz) | OP_C(reg) |
		OP_B(reg_mem) | STORE_S9(off);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* st.aw reg, [sp, -4] */
static u8 arc_push_r(u8 *buf, u8 reg)
{
	const u32 insn = OPC_PUSH | OP_C(reg);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* ld reg, [reg_mem, off] (unsigned) */
static u8 arc_ld_r(u8 *buf, u8 reg, u8 reg_mem, s16 off, u8 zz)
{
	const u32 insn = OPC_LDU | LOAD_ZZ(zz) | LOAD_C(reg) |
		OP_B(reg_mem) | LOAD_S9(off);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* ld.x reg, [reg_mem, off] (sign extend) */
static u8 arc_ldx_r(u8 *buf, u8 reg, u8 reg_mem, s16 off, u8 zz)
{
	const u32 insn = OPC_LDS | LOAD_ZZ(zz) | LOAD_C(reg) |
		OP_B(reg_mem) | LOAD_S9(off);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* ld.ab reg,[sp,4] */
static u8 arc_pop_r(u8 *buf, u8 reg)
{
	const u32 insn = OPC_POP | LOAD_C(reg);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* add Ra,Ra,Rc */
static u8 arc_add_r(u8 *buf, u8 ra, u8 rc)
{
	const u32 insn = OPC_ADD | OP_A(ra) | OP_B(ra) | OP_C(rc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* add.f Ra,Ra,Rc */
static u8 arc_addf_r(u8 *buf, u8 ra, u8 rc)
{
	const u32 insn = OPC_ADDF | OP_A(ra) | OP_B(ra) | OP_C(rc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* add.f Ra,Ra,u6 */
static u8 arc_addif_r(u8 *buf, u8 ra, u8 u6)
{
	const u32 insn = OPC_ADDIF | OP_A(ra) | OP_B(ra) | ADDI_U6(u6);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* add Ra,Ra,u6 */
static u8 arc_addi_r(u8 *buf, u8 ra, u8 u6)
{
	const u32 insn = OPC_ADDI | OP_A(ra) | OP_B(ra) | ADDI_U6(u6);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* add Ra,Rb,imm */
static u8 arc_add_i(u8 *buf, u8 ra, u8 rb, s32 imm)
{
	const u32 insn = OPC_ADD_I | OP_A(ra) | OP_B(rb);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* adc Ra,Ra,Rc */
static u8 arc_adc_r(u8 *buf, u8 ra, u8 rc)
{
	const u32 insn = OPC_ADC | OP_A(ra) | OP_B(ra) | OP_C(rc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* adc Ra,Ra,u6 */
static u8 arc_adci_r(u8 *buf, u8 ra, u8 u6)
{
	const u32 insn = OPC_ADCI | OP_A(ra) | OP_B(ra) | ADCI_U6(u6);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* sub Ra,Ra,Rc */
static u8 arc_sub_r(u8 *buf, u8 ra, u8 rc)
{
	const u32 insn = OPC_SUB | OP_A(ra) | OP_B(ra) | OP_C(rc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* sub.f Ra,Ra,Rc */
static u8 arc_subf_r(u8 *buf, u8 ra, u8 rc)
{
	const u32 insn = OPC_SUBF | OP_A(ra) | OP_B(ra) | OP_C(rc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* sub Ra,Ra,u6 */
static u8 arc_subi_r(u8 *buf, u8 ra, u8 u6)
{
	const u32 insn = OPC_SUBI | OP_A(ra) | OP_B(ra) | SUBI_U6(u6);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* sub Ra,Ra,imm */
static u8 arc_sub_i(u8 *buf, u8 ra, s32 imm)
{
	const u32 insn = OPC_SUB_I | OP_A(ra) | OP_B(ra);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* sbc Ra,Ra,Rc */
static u8 arc_sbc_r(u8 *buf, u8 ra, u8 rc)
{
	const u32 insn = OPC_SBC | OP_A(ra) | OP_B(ra) | OP_C(rc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* cmp Rb,Rc */
static u8 arc_cmp_r(u8 *buf, u8 rb, u8 rc)
{
	const u32 insn = OPC_CMP | OP_B(rb) | OP_C(rc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/*
 * cmp.z Rb,Rc
 *
 * This "cmp.z" variant of compare instruction is used on lower
 * 32-bits of register pairs after "cmp"ing their upper parts. If the
 * upper parts are equal (z), then this one will proceed to check the
 * rest.
 */
static u8 arc_cmpz_r(u8 *buf, u8 rb, u8 rc)
{
	const u32 insn = OPC_CMP | OP_B(rb) | OP_C(rc) | CC_equal;

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* neg Ra,Rb */
static u8 arc_neg_r(u8 *buf, u8 ra, u8 rb)
{
	const u32 insn = OPC_NEG | OP_A(ra) | OP_B(rb);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* mpy Ra,Rb,Rc */
static u8 arc_mpy_r(u8 *buf, u8 ra, u8 rb, u8 rc)
{
	const u32 insn = OPC_MPY | OP_A(ra) | OP_B(rb) | OP_C(rc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* mpy Ra,Rb,imm */
static u8 arc_mpy_i(u8 *buf, u8 ra, u8 rb, s32 imm)
{
	const u32 insn = OPC_MPYI | OP_A(ra) | OP_B(rb);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* mpydu Ra,Ra,Rc */
static u8 arc_mpydu_r(u8 *buf, u8 ra, u8 rc)
{
	const u32 insn = OPC_MPYDU | OP_A(ra) | OP_B(ra) | OP_C(rc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* mpydu Ra,Ra,imm */
static u8 arc_mpydu_i(u8 *buf, u8 ra, s32 imm)
{
	const u32 insn = OPC_MPYDUI | OP_A(ra) | OP_B(ra);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* divu Rd,Rd,Rs */
static u8 arc_divu_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_DIVU | OP_A(rd) | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* divu Rd,Rd,imm */
static u8 arc_divu_i(u8 *buf, u8 rd, s32 imm)
{
	const u32 insn = OPC_DIVUI | OP_A(rd) | OP_B(rd);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* div Rd,Rd,Rs */
static u8 arc_divs_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_DIVS | OP_A(rd) | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* div Rd,Rd,imm */
static u8 arc_divs_i(u8 *buf, u8 rd, s32 imm)
{
	const u32 insn = OPC_DIVSI | OP_A(rd) | OP_B(rd);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* remu Rd,Rd,Rs */
static u8 arc_remu_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_REMU | OP_A(rd) | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* remu Rd,Rd,imm */
static u8 arc_remu_i(u8 *buf, u8 rd, s32 imm)
{
	const u32 insn = OPC_REMUI | OP_A(rd) | OP_B(rd);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* rem Rd,Rd,Rs */
static u8 arc_rems_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_REMS | OP_A(rd) | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* rem Rd,Rd,imm */
static u8 arc_rems_i(u8 *buf, u8 rd, s32 imm)
{
	const u32 insn = OPC_REMSI | OP_A(rd) | OP_B(rd);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* and Rd,Rd,Rs */
static u8 arc_and_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_AND | OP_A(rd) | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/* and Rd,Rd,limm */
static u8 arc_and_i(u8 *buf, u8 rd, s32 imm)
{
	const u32 insn = OPC_ANDI | OP_A(rd) | OP_B(rd);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

/* tst Rd,Rs */
static u8 arc_tst_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_TST | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/*
 * This particular version, "tst.z ...", is meant to be used after a
 * "tst" on the low 32-bit of register pairs. If that "tst" is not
 * zero, then we don't need to test the upper 32-bits lest it sets
 * the zero flag.
 */
static u8 arc_tstz_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_TST | OP_B(rd) | OP_C(rs) | CC_equal;

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_or_r(u8 *buf, u8 rd, u8 rs1, u8 rs2)
{
	const u32 insn = OPC_OR | OP_A(rd) | OP_B(rs1) | OP_C(rs2);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_or_i(u8 *buf, u8 rd, s32 imm)
{
	const u32 insn = OPC_ORI | OP_A(rd) | OP_B(rd);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

static u8 arc_xor_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_XOR | OP_A(rd) | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_xor_i(u8 *buf, u8 rd, s32 imm)
{
	const u32 insn = OPC_XORI | OP_A(rd) | OP_B(rd);

	if (buf) {
		emit_4_bytes(buf, insn);
		emit_4_bytes(buf + INSN_len_normal, imm);
	}
	return INSN_len_normal + INSN_len_imm;
}

static u8 arc_not_r(u8 *buf, u8 rd, u8 rs)
{
	const u32 insn = OPC_NOT | OP_B(rd) | OP_C(rs);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_btst_i(u8 *buf, u8 rs, u8 imm)
{
	const u32 insn = OPC_BTSTU6 | OP_B(rs) | BTST_U6(imm);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_asl_r(u8 *buf, u8 rd, u8 rs1, u8 rs2)
{
	const u32 insn = OPC_ASL | OP_A(rd) | OP_B(rs1) | OP_C(rs2);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_asli_r(u8 *buf, u8 rd, u8 rs, u8 imm)
{
	const u32 insn = OPC_ASLI | OP_A(rd) | OP_B(rs) | ASLI_U6(imm);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_asr_r(u8 *buf, u8 rd, u8 rs1, u8 rs2)
{
	const u32 insn = OPC_ASR | OP_A(rd) | OP_B(rs1) | OP_C(rs2);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_asri_r(u8 *buf, u8 rd, u8 rs, u8 imm)
{
	const u32 insn = OPC_ASRI | OP_A(rd) | OP_B(rs) | ASRI_U6(imm);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_lsr_r(u8 *buf, u8 rd, u8 rs1, u8 rs2)
{
	const u32 insn = OPC_LSR | OP_A(rd) | OP_B(rs1) | OP_C(rs2);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_lsri_r(u8 *buf, u8 rd, u8 rs, u8 imm)
{
	const u32 insn = OPC_LSRI | OP_A(rd) | OP_B(rs) | LSRI_U6(imm);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_swape_r(u8 *buf, u8 r)
{
	const u32 insn = OPC_SWAPE | OP_B(r) | OP_C(r);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

static u8 arc_jmp_return(u8 *buf)
{
	if (buf)
		emit_4_bytes(buf, OPC_J_BLINK);
	return INSN_len_normal;
}

static u8 arc_jl(u8 *buf, u8 reg)
{
	const u32 insn = OPC_JL | OP_C(reg);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/*
 * Conditional jump to an address that is max 21 bits away (signed).
 *
 * b<cc> s21
 */
static u8 arc_bcc(u8 *buf, u8 cc, int offset)
{
	const u32 insn = OPC_BCC | BCC_S21(offset) | COND(cc);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/*
 * Unconditional jump to an address that is max 25 bits away (signed).
 *
 * b     s25
 */
static u8 arc_b(u8 *buf, s32 offset)
{
	const u32 insn = OPC_B | B_S25(offset);

	if (buf)
		emit_4_bytes(buf, insn);
	return INSN_len_normal;
}

/************* Packers (Deal with BPF_REGs) **************/

u8 zext(u8 *buf, u8 rd)
{
	if (rd != BPF_REG_FP)
		return arc_movi_r(buf, REG_HI(rd), 0);
	else
		return 0;
}

u8 mov_r32(u8 *buf, u8 rd, u8 rs, u8 sign_ext)
{
	u8 len = 0;

	if (sign_ext) {
		if (sign_ext == 8)
			len = arc_sexb_r(buf, REG_LO(rd), REG_LO(rs));
		else if (sign_ext == 16)
			len = arc_sexh_r(buf, REG_LO(rd), REG_LO(rs));
		else if (sign_ext == 32 && rd != rs)
			len = arc_mov_r(buf, REG_LO(rd), REG_LO(rs));

		return len;
	}

	/* Unsigned move. */

	if (rd != rs)
		len = arc_mov_r(buf, REG_LO(rd), REG_LO(rs));

	return len;
}

u8 mov_r32_i32(u8 *buf, u8 reg, s32 imm)
{
	return arc_mov_i(buf, REG_LO(reg), imm);
}

u8 mov_r64(u8 *buf, u8 rd, u8 rs, u8 sign_ext)
{
	u8 len = 0;

	if (sign_ext) {
		/* First handle the low 32-bit part. */
		len = mov_r32(buf, rd, rs, sign_ext);

		/* Now propagate the sign bit of LO to HI. */
		if (sign_ext == 8 || sign_ext == 16 || sign_ext == 32) {
			len += arc_asri_r(BUF(buf, len),
					  REG_HI(rd), REG_LO(rd), 31);
		}

		return len;
	}

	/* Unsigned move. */

	if (rd == rs)
		return 0;

	len = arc_mov_r(buf, REG_LO(rd), REG_LO(rs));

	if (rs != BPF_REG_FP)
		len += arc_mov_r(BUF(buf, len), REG_HI(rd), REG_HI(rs));
	/* BPF_REG_FP is mapped to 32-bit "fp" register. */
	else
		len += arc_movi_r(BUF(buf, len), REG_HI(rd), 0);

	return len;
}

/* Sign extend the 32-bit immediate into 64-bit register pair. */
u8 mov_r64_i32(u8 *buf, u8 reg, s32 imm)
{
	u8 len = 0;

	len = arc_mov_i(buf, REG_LO(reg), imm);

	/* BPF_REG_FP is mapped to 32-bit "fp" register. */
	if (reg != BPF_REG_FP) {
		if (imm >= 0)
			len += arc_movi_r(BUF(buf, len), REG_HI(reg), 0);
		else
			len += arc_movi_r(BUF(buf, len), REG_HI(reg), -1);
	}

	return len;
}

/*
 * This is merely used for translation of "LD R, IMM64" instructions
 * of the BPF. These sort of instructions are sometimes used for
 * relocations. If during the normal pass, the relocation value is
 * not known, the BPF instruction may look something like:
 *
 * LD R <- 0x0000_0001_0000_0001
 *
 * Which will nicely translate to two 4-byte ARC instructions:
 *
 * mov R_lo, 1               # imm is small enough to be s12
 * mov R_hi, 1               # same
 *
 * However, during the extra pass, the IMM64 will have changed
 * to the resolved address and looks something like:
 *
 * LD R <- 0x0000_0000_1234_5678
 *
 * Now, the translated code will require 12 bytes:
 *
 * mov R_lo, 0x12345678      # this is an 8-byte instruction
 * mov R_hi, 0               # still 4 bytes
 *
 * Which in practice will result in overwriting the following
 * instruction. To avoid such cases, we will always emit codes
 * with fixed sizes.
 */
u8 mov_r64_i64(u8 *buf, u8 reg, u32 lo, u32 hi)
{
	u8 len;

	len  = arc_mov_i_fixed(buf, REG_LO(reg), lo);
	len += arc_mov_i_fixed(BUF(buf, len), REG_HI(reg), hi);

	return len;
}

/*
 * If the "off"set is too big (doesn't encode as S9) for:
 *
 *   {ld,st}  r, [rm, off]
 *
 * Then emit:
 *
 *   add r10, REG_LO(rm), off
 *
 * and make sure that r10 becomes the effective address:
 *
 *   {ld,st}  r, [r10, 0]
 */
static u8 adjust_mem_access(u8 *buf, s16 *off, u8 size,
			    u8 rm, u8 *arc_reg_mem)
{
	u8 len = 0;
	*arc_reg_mem = REG_LO(rm);

	if (!IN_S9_RANGE(*off) ||
	    (size == BPF_DW && !IN_S9_RANGE(*off + 4))) {
		len += arc_add_i(BUF(buf, len),
				 REG_LO(JIT_REG_TMP), REG_LO(rm), (u32)(*off));
		*arc_reg_mem = REG_LO(JIT_REG_TMP);
		*off = 0;
	}

	return len;
}

/* store rs, [rd, off] */
u8 store_r(u8 *buf, u8 rs, u8 rd, s16 off, u8 size)
{
	u8 len, arc_reg_mem;

	len = adjust_mem_access(buf, &off, size, rd, &arc_reg_mem);

	if (size == BPF_DW) {
		len += arc_st_r(BUF(buf, len), REG_LO(rs), arc_reg_mem,
				off, ZZ_4_byte);
		len += arc_st_r(BUF(buf, len), REG_HI(rs), arc_reg_mem,
				off + 4, ZZ_4_byte);
	} else {
		u8 zz = bpf_to_arc_size(size);

		len += arc_st_r(BUF(buf, len), REG_LO(rs), arc_reg_mem,
				off, zz);
	}

	return len;
}

/*
 * For {8,16,32}-bit stores:
 *   mov r21, imm
 *   st  r21, [...]
 * For 64-bit stores:
 *   mov r21, imm
 *   st  r21, [...]
 *   mov r21, {0,-1}
 *   st  r21, [...+4]
 */
u8 store_i(u8 *buf, s32 imm, u8 rd, s16 off, u8 size)
{
	u8 len, arc_reg_mem;
	/* REG_LO(JIT_REG_TMP) might be used by "adjust_mem_access()". */
	const u8 arc_rs = REG_HI(JIT_REG_TMP);

	len = adjust_mem_access(buf, &off, size, rd, &arc_reg_mem);

	if (size == BPF_DW) {
		len += arc_mov_i(BUF(buf, len), arc_rs, imm);
		len += arc_st_r(BUF(buf, len), arc_rs, arc_reg_mem,
				off, ZZ_4_byte);
		imm = (imm >= 0 ? 0 : -1);
		len += arc_mov_i(BUF(buf, len), arc_rs, imm);
		len += arc_st_r(BUF(buf, len), arc_rs, arc_reg_mem,
				off + 4, ZZ_4_byte);
	} else {
		u8 zz = bpf_to_arc_size(size);

		len += arc_mov_i(BUF(buf, len), arc_rs, imm);
		len += arc_st_r(BUF(buf, len), arc_rs, arc_reg_mem, off, zz);
	}

	return len;
}

/*
 * For the calling convention of a little endian machine, the LO part
 * must be on top of the stack.
 */
static u8 push_r64(u8 *buf, u8 reg)
{
	u8 len = 0;

#ifdef __LITTLE_ENDIAN
	/* BPF_REG_FP is mapped to 32-bit "fp" register. */
	if (reg != BPF_REG_FP)
		len += arc_push_r(BUF(buf, len), REG_HI(reg));
	len += arc_push_r(BUF(buf, len), REG_LO(reg));
#else
	len += arc_push_r(BUF(buf, len), REG_LO(reg));
	if (reg != BPF_REG_FP)
		len += arc_push_r(BUF(buf, len), REG_HI(reg));
#endif

	return len;
}

/* load rd, [rs, off] */
u8 load_r(u8 *buf, u8 rd, u8 rs, s16 off, u8 size, bool sign_ext)
{
	u8 len, arc_reg_mem;

	len = adjust_mem_access(buf, &off, size, rs, &arc_reg_mem);

	if (size == BPF_B || size == BPF_H || size == BPF_W) {
		const u8 zz = bpf_to_arc_size(size);

		/* Use LD.X only if the data size is less than 32-bit. */
		if (sign_ext && (zz == ZZ_1_byte || zz == ZZ_2_byte)) {
			len += arc_ldx_r(BUF(buf, len), REG_LO(rd),
					 arc_reg_mem, off, zz);
		} else {
			len += arc_ld_r(BUF(buf, len), REG_LO(rd),
					arc_reg_mem, off, zz);
		}

		if (sign_ext) {
			/* Propagate the sign bit to the higher reg. */
			len += arc_asri_r(BUF(buf, len),
					  REG_HI(rd), REG_LO(rd), 31);
		} else {
			len += arc_movi_r(BUF(buf, len), REG_HI(rd), 0);
		}
	} else if (size == BPF_DW) {
		/*
		 * We are about to issue 2 consecutive loads:
		 *
		 *   ld rx, [rb, off+0]
		 *   ld ry, [rb, off+4]
		 *
		 * If "rx" and "rb" are the same registers, then the order
		 * should change to guarantee that "rb" remains intact
		 * during these 2 operations:
		 *
		 *   ld ry, [rb, off+4]
		 *   ld rx, [rb, off+0]
		 */
		if (REG_LO(rd) != arc_reg_mem) {
			len += arc_ld_r(BUF(buf, len), REG_LO(rd), arc_reg_mem,
					off, ZZ_4_byte);
			len += arc_ld_r(BUF(buf, len), REG_HI(rd), arc_reg_mem,
					off + 4, ZZ_4_byte);
		} else {
			len += arc_ld_r(BUF(buf, len), REG_HI(rd), arc_reg_mem,
					off + 4, ZZ_4_byte);
			len += arc_ld_r(BUF(buf, len), REG_LO(rd), arc_reg_mem,
					off, ZZ_4_byte);
		}
	}

	return len;
}

u8 add_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_add_r(buf, REG_LO(rd), REG_LO(rs));
}

u8 add_r32_i32(u8 *buf, u8 rd, s32 imm)
{
	if (IN_U6_RANGE(imm))
		return arc_addi_r(buf, REG_LO(rd), imm);
	else
		return arc_add_i(buf, REG_LO(rd), REG_LO(rd), imm);
}

u8 add_r64(u8 *buf, u8 rd, u8 rs)
{
	u8 len;

	len  = arc_addf_r(buf, REG_LO(rd), REG_LO(rs));
	len += arc_adc_r(BUF(buf, len), REG_HI(rd), REG_HI(rs));
	return len;
}

u8 add_r64_i32(u8 *buf, u8 rd, s32 imm)
{
	u8 len;

	if (IN_U6_RANGE(imm)) {
		len  = arc_addif_r(buf, REG_LO(rd), imm);
		len += arc_adci_r(BUF(buf, len), REG_HI(rd), 0);
	} else {
		len  = mov_r64_i32(buf, JIT_REG_TMP, imm);
		len += add_r64(BUF(buf, len), rd, JIT_REG_TMP);
	}
	return len;
}

u8 sub_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_sub_r(buf, REG_LO(rd), REG_LO(rs));
}

u8 sub_r32_i32(u8 *buf, u8 rd, s32 imm)
{
	if (IN_U6_RANGE(imm))
		return arc_subi_r(buf, REG_LO(rd), imm);
	else
		return arc_sub_i(buf, REG_LO(rd), imm);
}

u8 sub_r64(u8 *buf, u8 rd, u8 rs)
{
	u8 len;

	len  = arc_subf_r(buf, REG_LO(rd), REG_LO(rs));
	len += arc_sbc_r(BUF(buf, len), REG_HI(rd), REG_HI(rs));
	return len;
}

u8 sub_r64_i32(u8 *buf, u8 rd, s32 imm)
{
	u8 len;

	len  = mov_r64_i32(buf, JIT_REG_TMP, imm);
	len += sub_r64(BUF(buf, len), rd, JIT_REG_TMP);
	return len;
}

static u8 cmp_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_cmp_r(buf, REG_LO(rd), REG_LO(rs));
}

u8 neg_r32(u8 *buf, u8 r)
{
	return arc_neg_r(buf, REG_LO(r), REG_LO(r));
}

/* In a two's complement system, -r is (~r + 1). */
u8 neg_r64(u8 *buf, u8 r)
{
	u8 len;

	len  = arc_not_r(buf, REG_LO(r), REG_LO(r));
	len += arc_not_r(BUF(buf, len), REG_HI(r), REG_HI(r));
	len += add_r64_i32(BUF(buf, len), r, 1);
	return len;
}

u8 mul_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_mpy_r(buf, REG_LO(rd), REG_LO(rd), REG_LO(rs));
}

u8 mul_r32_i32(u8 *buf, u8 rd, s32 imm)
{
	return arc_mpy_i(buf, REG_LO(rd), REG_LO(rd), imm);
}

/*
 * MUL B, C
 * --------
 * mpy       t0, B_hi, C_lo
 * mpy       t1, B_lo, C_hi
 * mpydu   B_lo, B_lo, C_lo
 * add     B_hi, B_hi,   t0
 * add     B_hi, B_hi,   t1
 */
u8 mul_r64(u8 *buf, u8 rd, u8 rs)
{
	const u8 t0   = REG_LO(JIT_REG_TMP);
	const u8 t1   = REG_HI(JIT_REG_TMP);
	const u8 C_lo = REG_LO(rs);
	const u8 C_hi = REG_HI(rs);
	const u8 B_lo = REG_LO(rd);
	const u8 B_hi = REG_HI(rd);
	u8 len;

	len  = arc_mpy_r(buf, t0, B_hi, C_lo);
	len += arc_mpy_r(BUF(buf, len), t1, B_lo, C_hi);
	len += arc_mpydu_r(BUF(buf, len), B_lo, C_lo);
	len += arc_add_r(BUF(buf, len), B_hi, t0);
	len += arc_add_r(BUF(buf, len), B_hi, t1);

	return len;
}

/*
 * MUL B, imm
 * ----------
 *
 *  To get a 64-bit result from a signed 64x32 multiplication:
 *
 *         B_hi             B_lo   *
 *         sign             imm
 *  -----------------------------
 *  HI(B_lo*imm)     LO(B_lo*imm)  +
 *     B_hi*imm                    +
 *     B_lo*sign
 *  -----------------------------
 *        res_hi           res_lo
 *
 * mpy     t1, B_lo, sign(imm)
 * mpy     t0, B_hi, imm
 * mpydu B_lo, B_lo, imm
 * add   B_hi, B_hi,  t0
 * add   B_hi, B_hi,  t1
 *
 * Note: We can't use signed double multiplication, "mpyd", instead of an
 * unsigned version, "mpydu", and then get rid of the sign adjustments
 * calculated in "t1". The signed multiplication, "mpyd", will consider
 * both operands, "B_lo" and "imm", as signed inputs. However, for this
 * 64x32 multiplication, "B_lo" must be treated as an unsigned number.
 */
u8 mul_r64_i32(u8 *buf, u8 rd, s32 imm)
{
	const u8 t0   = REG_LO(JIT_REG_TMP);
	const u8 t1   = REG_HI(JIT_REG_TMP);
	const u8 B_lo = REG_LO(rd);
	const u8 B_hi = REG_HI(rd);
	u8 len = 0;

	if (imm == 1)
		return 0;

	/* Is the sign-extension of the immediate "-1"? */
	if (imm < 0)
		len += arc_neg_r(BUF(buf, len), t1, B_lo);

	len += arc_mpy_i(BUF(buf, len), t0, B_hi, imm);
	len += arc_mpydu_i(BUF(buf, len), B_lo, imm);
	len += arc_add_r(BUF(buf, len), B_hi, t0);

	/* Add the "sign*B_lo" part, if necessary. */
	if (imm < 0)
		len += arc_add_r(BUF(buf, len), B_hi, t1);

	return len;
}

u8 div_r32(u8 *buf, u8 rd, u8 rs, bool sign_ext)
{
	if (sign_ext)
		return arc_divs_r(buf, REG_LO(rd), REG_LO(rs));
	else
		return arc_divu_r(buf, REG_LO(rd), REG_LO(rs));
}

u8 div_r32_i32(u8 *buf, u8 rd, s32 imm, bool sign_ext)
{
	if (imm == 0)
		return 0;

	if (sign_ext)
		return arc_divs_i(buf, REG_LO(rd), imm);
	else
		return arc_divu_i(buf, REG_LO(rd), imm);
}

u8 mod_r32(u8 *buf, u8 rd, u8 rs, bool sign_ext)
{
	if (sign_ext)
		return arc_rems_r(buf, REG_LO(rd), REG_LO(rs));
	else
		return arc_remu_r(buf, REG_LO(rd), REG_LO(rs));
}

u8 mod_r32_i32(u8 *buf, u8 rd, s32 imm, bool sign_ext)
{
	if (imm == 0)
		return 0;

	if (sign_ext)
		return arc_rems_i(buf, REG_LO(rd), imm);
	else
		return arc_remu_i(buf, REG_LO(rd), imm);
}

u8 and_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_and_r(buf, REG_LO(rd), REG_LO(rs));
}

u8 and_r32_i32(u8 *buf, u8 rd, s32 imm)
{
	return arc_and_i(buf, REG_LO(rd), imm);
}

u8 and_r64(u8 *buf, u8 rd, u8 rs)
{
	u8 len;

	len  = arc_and_r(buf, REG_LO(rd), REG_LO(rs));
	len += arc_and_r(BUF(buf, len), REG_HI(rd), REG_HI(rs));
	return len;
}

u8 and_r64_i32(u8 *buf, u8 rd, s32 imm)
{
	u8 len;

	len  = mov_r64_i32(buf, JIT_REG_TMP, imm);
	len += and_r64(BUF(buf, len), rd, JIT_REG_TMP);
	return len;
}

static u8 tst_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_tst_r(buf, REG_LO(rd), REG_LO(rs));
}

u8 or_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_or_r(buf, REG_LO(rd), REG_LO(rd), REG_LO(rs));
}

u8 or_r32_i32(u8 *buf, u8 rd, s32 imm)
{
	return arc_or_i(buf, REG_LO(rd), imm);
}

u8 or_r64(u8 *buf, u8 rd, u8 rs)
{
	u8 len;

	len  = arc_or_r(buf, REG_LO(rd), REG_LO(rd), REG_LO(rs));
	len += arc_or_r(BUF(buf, len), REG_HI(rd), REG_HI(rd), REG_HI(rs));
	return len;
}

u8 or_r64_i32(u8 *buf, u8 rd, s32 imm)
{
	u8 len;

	len  = mov_r64_i32(buf, JIT_REG_TMP, imm);
	len += or_r64(BUF(buf, len), rd, JIT_REG_TMP);
	return len;
}

u8 xor_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_xor_r(buf, REG_LO(rd), REG_LO(rs));
}

u8 xor_r32_i32(u8 *buf, u8 rd, s32 imm)
{
	return arc_xor_i(buf, REG_LO(rd), imm);
}

u8 xor_r64(u8 *buf, u8 rd, u8 rs)
{
	u8 len;

	len  = arc_xor_r(buf, REG_LO(rd), REG_LO(rs));
	len += arc_xor_r(BUF(buf, len), REG_HI(rd), REG_HI(rs));
	return len;
}

u8 xor_r64_i32(u8 *buf, u8 rd, s32 imm)
{
	u8 len;

	len  = mov_r64_i32(buf, JIT_REG_TMP, imm);
	len += xor_r64(BUF(buf, len), rd, JIT_REG_TMP);
	return len;
}

/* "asl a,b,c" --> "a = (b << (c & 31))". */
u8 lsh_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_asl_r(buf, REG_LO(rd), REG_LO(rd), REG_LO(rs));
}

u8 lsh_r32_i32(u8 *buf, u8 rd, u8 imm)
{
	return arc_asli_r(buf, REG_LO(rd), REG_LO(rd), imm);
}

/*
 * algorithm
 * ---------
 * if (n <= 32)
 *   to_hi = lo >> (32-n)   # (32-n) is the negate of "n" in a 5-bit width.
 *   lo <<= n
 *   hi <<= n
 *   hi |= to_hi
 * else
 *   hi = lo << (n-32)
 *   lo = 0
 *
 * assembly translation for "LSH B, C"
 * (heavily influenced by ARC gcc)
 * -----------------------------------
 * not    t0, C_lo            # The first 3 lines are almost the same as:
 * lsr    t1, B_lo, 1         #   neg   t0, C_lo
 * lsr    t1, t1, t0          #   lsr   t1, B_lo, t0   --> t1 is "to_hi"
 * mov    t0, C_lo*           # with one important difference. In "neg"
 * asl    B_lo, B_lo, t0      # version, when C_lo=0, t1 becomes B_lo while
 * asl    B_hi, B_hi, t0      # it should be 0. The "not" approach instead,
 * or     B_hi, B_hi, t1      # "shift"s t1 once and 31 times, practically
 * btst   t0, 5               # setting it to 0 when C_lo=0.
 * mov.ne B_hi, B_lo**
 * mov.ne B_lo, 0
 *
 * *The "mov t0, C_lo" is necessary to cover the cases that C is the same
 * register as B.
 *
 * **ARC performs a shift in this manner: B <<= (C & 31)
 * For 32<=n<64, "n-32" and "n&31" are the same. Therefore, "B << n" and
 * "B << (n-32)" yield the same results. e.g. the results of "B << 35" and
 * "B << 3" are the same.
 *
 * The behaviour is undefined for n >= 64.
 */
u8 lsh_r64(u8 *buf, u8 rd, u8 rs)
{
	const u8 t0   = REG_LO(JIT_REG_TMP);
	const u8 t1   = REG_HI(JIT_REG_TMP);
	const u8 C_lo = REG_LO(rs);
	const u8 B_lo = REG_LO(rd);
	const u8 B_hi = REG_HI(rd);
	u8 len;

	len  = arc_not_r(buf, t0, C_lo);
	len += arc_lsri_r(BUF(buf, len), t1, B_lo, 1);
	len += arc_lsr_r(BUF(buf, len), t1, t1, t0);
	len += arc_mov_r(BUF(buf, len), t0, C_lo);
	len += arc_asl_r(BUF(buf, len), B_lo, B_lo, t0);
	len += arc_asl_r(BUF(buf, len), B_hi, B_hi, t0);
	len += arc_or_r(BUF(buf, len), B_hi, B_hi, t1);
	len += arc_btst_i(BUF(buf, len), t0, 5);
	len += arc_mov_cc_r(BUF(buf, len), CC_unequal, B_hi, B_lo);
	len += arc_movu_cc_r(BUF(buf, len), CC_unequal, B_lo, 0);

	return len;
}

/*
 * if (n < 32)
 *   to_hi = B_lo >> 32-n          # extract upper n bits
 *   lo <<= n
 *   hi <<=n
 *   hi |= to_hi
 * else if (n < 64)
 *   hi = lo << n-32
 *   lo = 0
 */
u8 lsh_r64_i32(u8 *buf, u8 rd, s32 imm)
{
	const u8 t0   = REG_LO(JIT_REG_TMP);
	const u8 B_lo = REG_LO(rd);
	const u8 B_hi = REG_HI(rd);
	const u8 n    = (u8)imm;
	u8 len = 0;

	if (n == 0) {
		return 0;
	} else if (n <= 31) {
		len  = arc_lsri_r(buf, t0, B_lo, 32 - n);
		len += arc_asli_r(BUF(buf, len), B_lo, B_lo, n);
		len += arc_asli_r(BUF(buf, len), B_hi, B_hi, n);
		len += arc_or_r(BUF(buf, len), B_hi, B_hi, t0);
	} else if (n <= 63) {
		len  = arc_asli_r(buf, B_hi, B_lo, n - 32);
		len += arc_movi_r(BUF(buf, len), B_lo, 0);
	}
	/* n >= 64 is undefined behaviour. */

	return len;
}

/* "lsr a,b,c" --> "a = (b >> (c & 31))". */
u8 rsh_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_lsr_r(buf, REG_LO(rd), REG_LO(rd), REG_LO(rs));
}

u8 rsh_r32_i32(u8 *buf, u8 rd, u8 imm)
{
	return arc_lsri_r(buf, REG_LO(rd), REG_LO(rd), imm);
}

/*
 * For better commentary, see lsh_r64().
 *
 * algorithm
 * ---------
 * if (n <= 32)
 *   to_lo = hi << (32-n)
 *   hi >>= n
 *   lo >>= n
 *   lo |= to_lo
 * else
 *   lo = hi >> (n-32)
 *   hi = 0
 *
 * RSH    B,C
 * ----------
 * not    t0, C_lo
 * asl    t1, B_hi, 1
 * asl    t1, t1, t0
 * mov    t0, C_lo
 * lsr    B_hi, B_hi, t0
 * lsr    B_lo, B_lo, t0
 * or     B_lo, B_lo, t1
 * btst   t0, 5
 * mov.ne B_lo, B_hi
 * mov.ne B_hi, 0
 */
u8 rsh_r64(u8 *buf, u8 rd, u8 rs)
{
	const u8 t0   = REG_LO(JIT_REG_TMP);
	const u8 t1   = REG_HI(JIT_REG_TMP);
	const u8 C_lo = REG_LO(rs);
	const u8 B_lo = REG_LO(rd);
	const u8 B_hi = REG_HI(rd);
	u8 len;

	len  = arc_not_r(buf, t0, C_lo);
	len += arc_asli_r(BUF(buf, len), t1, B_hi, 1);
	len += arc_asl_r(BUF(buf, len), t1, t1, t0);
	len += arc_mov_r(BUF(buf, len), t0, C_lo);
	len += arc_lsr_r(BUF(buf, len), B_hi, B_hi, t0);
	len += arc_lsr_r(BUF(buf, len), B_lo, B_lo, t0);
	len += arc_or_r(BUF(buf, len), B_lo, B_lo, t1);
	len += arc_btst_i(BUF(buf, len), t0, 5);
	len += arc_mov_cc_r(BUF(buf, len), CC_unequal, B_lo, B_hi);
	len += arc_movu_cc_r(BUF(buf, len), CC_unequal, B_hi, 0);

	return len;
}

/*
 * if (n < 32)
 *   to_lo = B_lo << 32-n     # extract lower n bits, right-padded with 32-n 0s
 *   lo >>=n
 *   hi >>=n
 *   hi |= to_lo
 * else if (n < 64)
 *   lo = hi >> n-32
 *   hi = 0
 */
u8 rsh_r64_i32(u8 *buf, u8 rd, s32 imm)
{
	const u8 t0   = REG_LO(JIT_REG_TMP);
	const u8 B_lo = REG_LO(rd);
	const u8 B_hi = REG_HI(rd);
	const u8 n    = (u8)imm;
	u8 len = 0;

	if (n == 0) {
		return 0;
	} else if (n <= 31) {
		len  = arc_asli_r(buf, t0, B_hi, 32 - n);
		len += arc_lsri_r(BUF(buf, len), B_lo, B_lo, n);
		len += arc_lsri_r(BUF(buf, len), B_hi, B_hi, n);
		len += arc_or_r(BUF(buf, len), B_lo, B_lo, t0);
	} else if (n <= 63) {
		len  = arc_lsri_r(buf, B_lo, B_hi, n - 32);
		len += arc_movi_r(BUF(buf, len), B_hi, 0);
	}
	/* n >= 64 is undefined behaviour. */

	return len;
}

/* "asr a,b,c" --> "a = (b s>> (c & 31))". */
u8 arsh_r32(u8 *buf, u8 rd, u8 rs)
{
	return arc_asr_r(buf, REG_LO(rd), REG_LO(rd), REG_LO(rs));
}

u8 arsh_r32_i32(u8 *buf, u8 rd, u8 imm)
{
	return arc_asri_r(buf, REG_LO(rd), REG_LO(rd), imm);
}

/*
 * For comparison, see rsh_r64().
 *
 * algorithm
 * ---------
 * if (n <= 32)
 *   to_lo = hi << (32-n)
 *   hi s>>= n
 *   lo  >>= n
 *   lo |= to_lo
 * else
 *   hi_sign = hi s>>31
 *   lo = hi s>> (n-32)
 *   hi = hi_sign
 *
 * ARSH   B,C
 * ----------
 * not    t0, C_lo
 * asl    t1, B_hi, 1
 * asl    t1, t1, t0
 * mov    t0, C_lo
 * asr    B_hi, B_hi, t0
 * lsr    B_lo, B_lo, t0
 * or     B_lo, B_lo, t1
 * btst   t0, 5
 * asr    t0, B_hi, 31        # now, t0 = 0 or -1 based on B_hi's sign
 * mov.ne B_lo, B_hi
 * mov.ne B_hi, t0
 */
u8 arsh_r64(u8 *buf, u8 rd, u8 rs)
{
	const u8 t0   = REG_LO(JIT_REG_TMP);
	const u8 t1   = REG_HI(JIT_REG_TMP);
	const u8 C_lo = REG_LO(rs);
	const u8 B_lo = REG_LO(rd);
	const u8 B_hi = REG_HI(rd);
	u8 len;

	len  = arc_not_r(buf, t0, C_lo);
	len += arc_asli_r(BUF(buf, len), t1, B_hi, 1);
	len += arc_asl_r(BUF(buf, len), t1, t1, t0);
	len += arc_mov_r(BUF(buf, len), t0, C_lo);
	len += arc_asr_r(BUF(buf, len), B_hi, B_hi, t0);
	len += arc_lsr_r(BUF(buf, len), B_lo, B_lo, t0);
	len += arc_or_r(BUF(buf, len), B_lo, B_lo, t1);
	len += arc_btst_i(BUF(buf, len), t0, 5);
	len += arc_asri_r(BUF(buf, len), t0, B_hi, 31);
	len += arc_mov_cc_r(BUF(buf, len), CC_unequal, B_lo, B_hi);
	len += arc_mov_cc_r(BUF(buf, len), CC_unequal, B_hi, t0);

	return len;
}

/*
 * if (n < 32)
 *   to_lo = lo << 32-n     # extract lower n bits, right-padded with 32-n 0s
 *   lo >>=n
 *   hi s>>=n
 *   hi |= to_lo
 * else if (n < 64)
 *   lo = hi s>> n-32
 *   hi = (lo[msb] ? -1 : 0)
 */
u8 arsh_r64_i32(u8 *buf, u8 rd, s32 imm)
{
	const u8 t0   = REG_LO(JIT_REG_TMP);
	const u8 B_lo = REG_LO(rd);
	const u8 B_hi = REG_HI(rd);
	const u8 n    = (u8)imm;
	u8 len = 0;

	if (n == 0) {
		return 0;
	} else if (n <= 31) {
		len  = arc_asli_r(buf, t0, B_hi, 32 - n);
		len += arc_lsri_r(BUF(buf, len), B_lo, B_lo, n);
		len += arc_asri_r(BUF(buf, len), B_hi, B_hi, n);
		len += arc_or_r(BUF(buf, len), B_lo, B_lo, t0);
	} else if (n <= 63) {
		len  = arc_asri_r(buf, B_lo, B_hi, n - 32);
		len += arc_movi_r(BUF(buf, len), B_hi, -1);
		len += arc_btst_i(BUF(buf, len), B_lo, 31);
		len += arc_movu_cc_r(BUF(buf, len), CC_equal, B_hi, 0);
	}
	/* n >= 64 is undefined behaviour. */

	return len;
}

u8 gen_swap(u8 *buf, u8 rd, u8 size, u8 endian, bool force, bool do_zext)
{
	u8 len = 0;
#ifdef __BIG_ENDIAN
	const u8 host_endian = BPF_FROM_BE;
#else
	const u8 host_endian = BPF_FROM_LE;
#endif
	if (host_endian != endian || force) {
		switch (size) {
		case 16:
			/*
			 * r = B4B3_B2B1 << 16 --> r = B2B1_0000
			 * then, swape(r) would become the desired 0000_B1B2
			 */
			len = arc_asli_r(buf, REG_LO(rd), REG_LO(rd), 16);
			fallthrough;
		case 32:
			len += arc_swape_r(BUF(buf, len), REG_LO(rd));
			if (do_zext)
				len += zext(BUF(buf, len), rd);
			break;
		case 64:
			/*
			 * swap "hi" and "lo":
			 *   hi ^= lo;
			 *   lo ^= hi;
			 *   hi ^= lo;
			 * and then swap the bytes in "hi" and "lo".
			 */
			len  = arc_xor_r(buf, REG_HI(rd), REG_LO(rd));
			len += arc_xor_r(BUF(buf, len), REG_LO(rd), REG_HI(rd));
			len += arc_xor_r(BUF(buf, len), REG_HI(rd), REG_LO(rd));
			len += arc_swape_r(BUF(buf, len), REG_LO(rd));
			len += arc_swape_r(BUF(buf, len), REG_HI(rd));
			break;
		default:
			/* The caller must have handled this. */
			break;
		}
	} else {
		/*
		 * If the same endianness, there's not much to do other
		 * than zeroing out the upper bytes based on the "size".
		 */
		switch (size) {
		case 16:
			len = arc_and_i(buf, REG_LO(rd), 0xffff);
			fallthrough;
		case 32:
			if (do_zext)
				len += zext(BUF(buf, len), rd);
			break;
		case 64:
			break;
		default:
			/* The caller must have handled this. */
			break;
		}
	}

	return len;
}

/*
 * To create a frame, all that is needed is:
 *
 *  push fp
 *  mov  fp, sp
 *  sub  sp, <frame_size>
 *
 * "push fp" is taken care of separately while saving the clobbered registers.
 * All that remains is copying SP value to FP and shrinking SP's address space
 * for any possible function call to come.
 */
static inline u8 frame_create(u8 *buf, u16 size)
{
	u8 len;

	len = arc_mov_r(buf, ARC_R_FP, ARC_R_SP);
	if (IN_U6_RANGE(size))
		len += arc_subi_r(BUF(buf, len), ARC_R_SP, size);
	else
		len += arc_sub_i(BUF(buf, len), ARC_R_SP, size);
	return len;
}

/*
 * mov sp, fp
 *
 * The value of SP upon entering was copied to FP.
 */
static inline u8 frame_restore(u8 *buf)
{
	return arc_mov_r(buf, ARC_R_SP, ARC_R_FP);
}

/*
 * Going from a JITed code to the native caller:
 *
 * mov ARC_ABI_RET_lo, BPF_REG_0_lo     # r0 <- r8
 * mov ARC_ABI_RET_hi, BPF_REG_0_hi     # r1 <- r9
 */
static u8 bpf_to_arc_return(u8 *buf)
{
	u8 len;

	len  = arc_mov_r(buf, ARC_R_0, REG_LO(BPF_REG_0));
	len += arc_mov_r(BUF(buf, len), ARC_R_1, REG_HI(BPF_REG_0));
	return len;
}

/*
 * Coming back from an external (in-kernel) function to the JITed code:
 *
 * mov ARC_ABI_RET_lo, BPF_REG_0_lo     # r8 <- r0
 * mov ARC_ABI_RET_hi, BPF_REG_0_hi     # r9 <- r1
 */
u8 arc_to_bpf_return(u8 *buf)
{
	u8 len;

	len  = arc_mov_r(buf, REG_LO(BPF_REG_0), ARC_R_0);
	len += arc_mov_r(BUF(buf, len), REG_HI(BPF_REG_0), ARC_R_1);
	return len;
}

/*
 * This translation leads to:
 *
 *   mov r10, addr                # always an 8-byte instruction
 *   jl  [r10]
 *
 * The length of the "mov" must be fixed (8), otherwise it may diverge
 * during the normal and extra passes:
 *
 *          normal pass                  extra pass
 *
 *   180:  mov     r10,0        |   180:  mov     r10,0x700578d8
 *   184:  jl      [r10]        |   188:  jl      [r10]
 *   188:  add.f   r16,r16,0x1  |   18c:  adc     r17,r17,0
 *   18c:  adc     r17,r17,0    |
 *
 * In the above example, the change from "r10 <- 0" to "r10 <- 0x700578d8"
 * has led to an increase in the length of the "mov" instruction.
 * Inadvertently, that caused the loss of the "add.f" instruction.
 */
static u8 jump_and_link(u8 *buf, u32 addr)
{
	u8 len;

	len  = arc_mov_i_fixed(buf, REG_LO(JIT_REG_TMP), addr);
	len += arc_jl(BUF(buf, len), REG_LO(JIT_REG_TMP));
	return len;
}

/*
 * This function determines which ARC registers must be saved and restored.
 * It does so by looking into:
 *
 * "bpf_reg": The clobbered (destination) BPF register
 * "is_call": Indicator if the current instruction is a call
 *
 * When a register of interest is clobbered, its corresponding bit position
 * in return value, "usage", is set to true.
 */
u32 mask_for_used_regs(u8 bpf_reg, bool is_call)
{
	u32 usage = 0;

	/* BPF registers that must be saved. */
	if (bpf_reg >= BPF_REG_6 && bpf_reg <= BPF_REG_9) {
		usage |= BIT(REG_LO(bpf_reg));
		usage |= BIT(REG_HI(bpf_reg));
	/*
	 * Using the frame pointer register implies that it should
	 * be saved and reinitialised with the current frame data.
	 */
	} else if (bpf_reg == BPF_REG_FP) {
		usage |= BIT(REG_LO(BPF_REG_FP));
	/* Could there be some ARC registers that must to be saved? */
	} else {
		if (REG_LO(bpf_reg) >= ARC_CALLEE_SAVED_REG_FIRST &&
		    REG_LO(bpf_reg) <= ARC_CALLEE_SAVED_REG_LAST)
			usage |= BIT(REG_LO(bpf_reg));

		if (REG_HI(bpf_reg) >= ARC_CALLEE_SAVED_REG_FIRST &&
		    REG_HI(bpf_reg) <= ARC_CALLEE_SAVED_REG_LAST)
			usage |= BIT(REG_HI(bpf_reg));
	}

	/* A "call" indicates that ARC's "blink" reg must be saved. */
	usage |= is_call ? BIT(ARC_R_BLINK) : 0;

	return usage;
}

/*
 * push blink             # if blink is marked as clobbered
 * push r[0-n]            # if r[i] is marked as clobbered
 * push fp                # if fp is marked as clobbered
 * mov  fp, sp            # if frame_size > 0 (clobbers fp)
 * sub  sp, <frame_size>  # same as above
 */
u8 arc_prologue(u8 *buf, u32 usage, u16 frame_size)
{
	u8 len = 0;
	u32 gp_regs = 0;

	/* Deal with blink first. */
	if (usage & BIT(ARC_R_BLINK))
		len += arc_push_r(BUF(buf, len), ARC_R_BLINK);

	gp_regs = usage & ~(BIT(ARC_R_BLINK) | BIT(ARC_R_FP));
	while (gp_regs) {
		u8 reg = __builtin_ffs(gp_regs) - 1;

		len += arc_push_r(BUF(buf, len), reg);
		gp_regs &= ~BIT(reg);
	}

	/* Deal with fp last. */
	if ((usage & BIT(ARC_R_FP)) || frame_size > 0)
		len += arc_push_r(BUF(buf, len), ARC_R_FP);

	if (frame_size > 0)
		len += frame_create(BUF(buf, len), frame_size);

#ifdef ARC_BPF_JIT_DEBUG
	if ((usage & BIT(ARC_R_FP)) && frame_size == 0) {
		pr_err("FP is being saved while there is no frame.");
		BUG();
	}
#endif

	return len;
}

/*
 * mov  sp, fp            # if frame_size > 0
 * pop  fp                # if fp is marked as clobbered
 * pop  r[n-0]            # if r[i] is marked as clobbered
 * pop  blink             # if blink is marked as clobbered
 * mov  r0, r8            # always: ABI_return <- BPF_return
 * mov  r1, r9            # continuation of above
 * j    [blink]           # always
 *
 * "fp being marked as clobbered" and "frame_size > 0" are the two sides of
 * the same coin.
 */
u8 arc_epilogue(u8 *buf, u32 usage, u16 frame_size)
{
	u32 len = 0;
	u32 gp_regs = 0;

#ifdef ARC_BPF_JIT_DEBUG
	if ((usage & BIT(ARC_R_FP)) && frame_size == 0) {
		pr_err("FP is being saved while there is no frame.");
		BUG();
	}
#endif

	if (frame_size > 0)
		len += frame_restore(BUF(buf, len));

	/* Deal with fp first. */
	if ((usage & BIT(ARC_R_FP)) || frame_size > 0)
		len += arc_pop_r(BUF(buf, len), ARC_R_FP);

	gp_regs = usage & ~(BIT(ARC_R_BLINK) | BIT(ARC_R_FP));
	while (gp_regs) {
		/* "usage" is 32-bit, each bit indicating an ARC register. */
		u8 reg = 31 - __builtin_clz(gp_regs);

		len += arc_pop_r(BUF(buf, len), reg);
		gp_regs &= ~BIT(reg);
	}

	/* Deal with blink last. */
	if (usage & BIT(ARC_R_BLINK))
		len += arc_pop_r(BUF(buf, len), ARC_R_BLINK);

	/* Wrap up the return value and jump back to the caller. */
	len += bpf_to_arc_return(BUF(buf, len));
	len += arc_jmp_return(BUF(buf, len));

	return len;
}

/*
 * For details on the algorithm, see the comments of "gen_jcc_64()".
 *
 * This data structure is holding information for jump translations.
 *
 * jit_off: How many bytes into the current JIT address, "b"ranch insn. occurs
 * cond: The condition that the ARC branch instruction must use
 *
 * e.g.:
 *
 * BPF_JGE  R1, R0, @target
 * ------------------------
 *            |
 *            v
 * 0x1000: cmp  r3, r1     # 0x1000 is the JIT address for "BPF_JGE ..." insn
 * 0x1004: bhi  @target    # first jump (branch higher)
 * 0x1008: blo  @end       # second jump acting as a skip (end is 0x1014)
 * 0x100C: cmp  r2, r0     # the lower 32 bits are evaluated
 * 0x1010: bhs  @target    # third jump (branch higher or same)
 * 0x1014: ...
 *
 * The jit_off(set) of the "bhi" is 4 bytes.
 * The cond(ition) for the "bhi" is "CC_great_u".
 *
 * The jit_off(set) is necessary for calculating the exact displacement
 * to the "target" address:
 *
 * jit_address + jit_off(set) - @target
 * 0x1000      + 4            - @target
 */
#define JCC64_NR_OF_JMPS 3	/* Number of jumps in jcc64 template. */
#define JCC64_INSNS_TO_END 3	/* Number of insn. inclusive the 2nd jmp to end. */
#define JCC64_SKIP_JMP 1	/* Index of the "skip" jump to "end". */
static const struct {
	/*
	 * "jit_off" is common between all "jmp[]" and is coupled with
	 * "cond" of each "jmp[]" instance. e.g.:
	 *
	 * arcv2_64_jccs.jit_off[1]
	 * arcv2_64_jccs.jmp[ARC_CC_UGT].cond[1]
	 *
	 * Are indicating that the second jump in JITed code of "UGT"
	 * is at offset "jit_off[1]" while its condition is "cond[1]".
	 */
	u8 jit_off[JCC64_NR_OF_JMPS];

	struct {
		u8 cond[JCC64_NR_OF_JMPS];
	} jmp[ARC_CC_SLE + 1];
} arcv2_64_jccs = {
	.jit_off = {
		INSN_len_normal * 1,
		INSN_len_normal * 2,
		INSN_len_normal * 4
	},
	/*
	 *   cmp  rd_hi, rs_hi
	 *   bhi  @target         # 1: u>
	 *   blo  @end            # 2: u<
	 *   cmp  rd_lo, rs_lo
	 *   bhi  @target         # 3: u>
	 * end:
	 */
	.jmp[ARC_CC_UGT] = {
		.cond = {CC_great_u, CC_less_u, CC_great_u}
	},
	/*
	 *   cmp  rd_hi, rs_hi
	 *   bhi  @target         # 1: u>
	 *   blo  @end            # 2: u<
	 *   cmp  rd_lo, rs_lo
	 *   bhs  @target         # 3: u>=
	 * end:
	 */
	.jmp[ARC_CC_UGE] = {
		.cond = {CC_great_u, CC_less_u, CC_great_eq_u}
	},
	/*
	 *   cmp  rd_hi, rs_hi
	 *   blo  @target         # 1: u<
	 *   bhi  @end            # 2: u>
	 *   cmp  rd_lo, rs_lo
	 *   blo  @target         # 3: u<
	 * end:
	 */
	.jmp[ARC_CC_ULT] = {
		.cond = {CC_less_u, CC_great_u, CC_less_u}
	},
	/*
	 *   cmp  rd_hi, rs_hi
	 *   blo  @target         # 1: u<
	 *   bhi  @end            # 2: u>
	 *   cmp  rd_lo, rs_lo
	 *   bls  @target         # 3: u<=
	 * end:
	 */
	.jmp[ARC_CC_ULE] = {
		.cond = {CC_less_u, CC_great_u, CC_less_eq_u}
	},
	/*
	 *   cmp  rd_hi, rs_hi
	 *   bgt  @target         # 1: s>
	 *   blt  @end            # 2: s<
	 *   cmp  rd_lo, rs_lo
	 *   bhi  @target         # 3: u>
	 * end:
	 */
	.jmp[ARC_CC_SGT] = {
		.cond = {CC_great_s, CC_less_s, CC_great_u}
	},
	/*
	 *   cmp  rd_hi, rs_hi
	 *   bgt  @target         # 1: s>
	 *   blt  @end            # 2: s<
	 *   cmp  rd_lo, rs_lo
	 *   bhs  @target         # 3: u>=
	 * end:
	 */
	.jmp[ARC_CC_SGE] = {
		.cond = {CC_great_s, CC_less_s, CC_great_eq_u}
	},
	/*
	 *   cmp  rd_hi, rs_hi
	 *   blt  @target         # 1: s<
	 *   bgt  @end            # 2: s>
	 *   cmp  rd_lo, rs_lo
	 *   blo  @target         # 3: u<
	 * end:
	 */
	.jmp[ARC_CC_SLT] = {
		.cond = {CC_less_s, CC_great_s, CC_less_u}
	},
	/*
	 *   cmp  rd_hi, rs_hi
	 *   blt  @target         # 1: s<
	 *   bgt  @end            # 2: s>
	 *   cmp  rd_lo, rs_lo
	 *   bls  @target         # 3: u<=
	 * end:
	 */
	.jmp[ARC_CC_SLE] = {
		.cond = {CC_less_s, CC_great_s, CC_less_eq_u}
	}
};

/*
 * The displacement (offset) for ARC's "b"ranch instruction is the distance
 * from the aligned version of _current_ instruction (PCL) to the target
 * instruction:
 *
 * DISP = TARGET - PCL          # PCL is the word aligned PC
 */
static inline s32 get_displacement(u32 curr_off, u32 targ_off)
{
	return (s32)(targ_off - (curr_off & ~3L));
}

/*
 * "disp"lacement should be:
 *
 * 1. 16-bit aligned.
 * 2. fit in S25, because no "condition code" is supposed to be encoded.
 */
static inline bool is_valid_far_disp(s32 disp)
{
	return (!(disp & 1) && IN_S25_RANGE(disp));
}

/*
 * "disp"lacement should be:
 *
 * 1. 16-bit aligned.
 * 2. fit in S21, because "condition code" is supposed to be encoded too.
 */
static inline bool is_valid_near_disp(s32 disp)
{
	return (!(disp & 1) && IN_S21_RANGE(disp));
}

/*
 * cmp        rd_hi, rs_hi
 * cmp.z      rd_lo, rs_lo
 * b{eq,ne}   @target
 *   |  |
 *   |  `-->  "eq" param is false (JNE)
 *   `----->  "eq" param is true  (JEQ)
 */
static int gen_j_eq_64(u8 *buf, u8 rd, u8 rs, bool eq,
		       u32 curr_off, u32 targ_off)
{
	s32 disp;
	u8 len = 0;

	len += arc_cmp_r(BUF(buf, len), REG_HI(rd), REG_HI(rs));
	len += arc_cmpz_r(BUF(buf, len), REG_LO(rd), REG_LO(rs));
	disp = get_displacement(curr_off + len, targ_off);
	len += arc_bcc(BUF(buf, len), eq ? CC_equal : CC_unequal, disp);

	return len;
}

/*
 * tst   rd_hi, rs_hi
 * tst.z rd_lo, rs_lo
 * bne   @target
 */
static u8 gen_jset_64(u8 *buf, u8 rd, u8 rs, u32 curr_off, u32 targ_off)
{
	u8 len = 0;
	s32 disp;

	len += arc_tst_r(BUF(buf, len), REG_HI(rd), REG_HI(rs));
	len += arc_tstz_r(BUF(buf, len), REG_LO(rd), REG_LO(rs));
	disp = get_displacement(curr_off + len, targ_off);
	len += arc_bcc(BUF(buf, len), CC_unequal, disp);

	return len;
}

/*
 * Verify if all the jumps for a JITed jcc64 operation are valid,
 * by consulting the data stored at "arcv2_64_jccs".
 */
static bool check_jcc_64(u32 curr_off, u32 targ_off, u8 cond)
{
	size_t i;

	if (cond >= ARC_CC_LAST)
		return false;

	for (i = 0; i < JCC64_NR_OF_JMPS; i++) {
		u32 from, to;

		from = curr_off + arcv2_64_jccs.jit_off[i];
		/* for the 2nd jump, we jump to the end of block. */
		if (i != JCC64_SKIP_JMP)
			to = targ_off;
		else
			to = from + (JCC64_INSNS_TO_END * INSN_len_normal);
		/* There is a "cc" in the instruction, so a "near" jump. */
		if (!is_valid_near_disp(get_displacement(from, to)))
			return false;
	}

	return true;
}

/* Can the jump from "curr_off" to "targ_off" actually happen? */
bool check_jmp_64(u32 curr_off, u32 targ_off, u8 cond)
{
	s32 disp;

	switch (cond) {
	case ARC_CC_UGT:
	case ARC_CC_UGE:
	case ARC_CC_ULT:
	case ARC_CC_ULE:
	case ARC_CC_SGT:
	case ARC_CC_SGE:
	case ARC_CC_SLT:
	case ARC_CC_SLE:
		return check_jcc_64(curr_off, targ_off, cond);
	case ARC_CC_EQ:
	case ARC_CC_NE:
	case ARC_CC_SET:
		/*
		 * The "jump" for the JITed BPF_J{SET,EQ,NE} is actually the
		 * 3rd instruction. See comments of "gen_j{set,_eq}_64()".
		 */
		curr_off += 2 * INSN_len_normal;
		disp = get_displacement(curr_off, targ_off);
		/* There is a "cc" field in the issued instruction. */
		return is_valid_near_disp(disp);
	case ARC_CC_AL:
		disp = get_displacement(curr_off, targ_off);
		return is_valid_far_disp(disp);
	default:
		return false;
	}
}

/*
 * The template for the 64-bit jumps with the following BPF conditions
 *
 * u< u<= u> u>= s< s<= s> s>=
 *
 * Looks like below:
 *
 *   cmp   rd_hi, rs_hi
 *   b<c1> @target
 *   b<c2> @end
 *   cmp   rd_lo, rs_lo   # if execution reaches here, r{d,s}_hi are equal
 *   b<c3> @target
 * end:
 *
 * "c1" is the condition that JIT is handling minus the equality part.
 * For instance if we have to translate an "unsigned greater or equal",
 * then "c1" will be "unsigned greater". We won't know about equality
 * until all 64-bits of data (higeher and lower registers) are processed.
 *
 * "c2" is the counter logic of "c1". For instance, if "c1" is originated
 * from "s>", then "c2" would be "s<". Notice that equality doesn't play
 * a role here either, because the lower 32 bits are not processed yet.
 *
 * "c3" is the unsigned version of "c1", no matter if the BPF condition
 * was signed or unsigned. An unsigned version is necessary, because the
 * MSB of the lower 32 bits does not reflect a sign in the whole 64-bit
 * scheme. Otherwise, 64-bit comparisons like
 * (0x0000_0000,0x8000_0000) s>= (0x0000_0000,0x0000_0000)
 * would yield an incorrect result. Finally, if there is an equality
 * check in the BPF condition, it will be reflected in "c3".
 *
 * You can find all the instances of this template where the
 * "arcv2_64_jccs" is getting initialised.
 */
static u8 gen_jcc_64(u8 *buf, u8 rd, u8 rs, u8 cond,
		     u32 curr_off, u32 targ_off)
{
	s32 disp;
	u32 end_off;
	const u8 *cc = arcv2_64_jccs.jmp[cond].cond;
	u8 len = 0;

	/* cmp rd_hi, rs_hi */
	len += arc_cmp_r(buf, REG_HI(rd), REG_HI(rs));

	/* b<c1> @target */
	disp = get_displacement(curr_off + len, targ_off);
	len += arc_bcc(BUF(buf, len), cc[0], disp);

	/* b<c2> @end */
	end_off = curr_off + len + (JCC64_INSNS_TO_END * INSN_len_normal);
	disp = get_displacement(curr_off + len, end_off);
	len += arc_bcc(BUF(buf, len), cc[1], disp);

	/* cmp rd_lo, rs_lo */
	len += arc_cmp_r(BUF(buf, len), REG_LO(rd), REG_LO(rs));

	/* b<c3> @target */
	disp = get_displacement(curr_off + len, targ_off);
	len += arc_bcc(BUF(buf, len), cc[2], disp);

	return len;
}

/*
 * This function only applies the necessary logic to make the proper
 * translations. All the sanity checks must have already been done
 * by calling the check_jmp_64().
 */
u8 gen_jmp_64(u8 *buf, u8 rd, u8 rs, u8 cond, u32 curr_off, u32 targ_off)
{
	u8 len = 0;
	bool eq = false;
	s32 disp;

	switch (cond) {
	case ARC_CC_AL:
		disp = get_displacement(curr_off, targ_off);
		len = arc_b(buf, disp);
		break;
	case ARC_CC_UGT:
	case ARC_CC_UGE:
	case ARC_CC_ULT:
	case ARC_CC_ULE:
	case ARC_CC_SGT:
	case ARC_CC_SGE:
	case ARC_CC_SLT:
	case ARC_CC_SLE:
		len = gen_jcc_64(buf, rd, rs, cond, curr_off, targ_off);
		break;
	case ARC_CC_EQ:
		eq = true;
		fallthrough;
	case ARC_CC_NE:
		len = gen_j_eq_64(buf, rd, rs, eq, curr_off, targ_off);
		break;
	case ARC_CC_SET:
		len = gen_jset_64(buf, rd, rs, curr_off, targ_off);
		break;
	default:
#ifdef ARC_BPF_JIT_DEBUG
		pr_err("64-bit jump condition is not known.");
		BUG();
#endif
	}
	return len;
}

/*
 * The condition codes to use when generating JIT instructions
 * for 32-bit jumps.
 *
 * The "ARC_CC_AL" index is not really used by the code, but it
 * is here for the sake of completeness.
 *
 * The "ARC_CC_SET" becomes "CC_unequal" because of the "tst"
 * instruction that precedes the conditional branch.
 */
static const u8 arcv2_32_jmps[ARC_CC_LAST] = {
	[ARC_CC_UGT] = CC_great_u,
	[ARC_CC_UGE] = CC_great_eq_u,
	[ARC_CC_ULT] = CC_less_u,
	[ARC_CC_ULE] = CC_less_eq_u,
	[ARC_CC_SGT] = CC_great_s,
	[ARC_CC_SGE] = CC_great_eq_s,
	[ARC_CC_SLT] = CC_less_s,
	[ARC_CC_SLE] = CC_less_eq_s,
	[ARC_CC_AL]  = CC_always,
	[ARC_CC_EQ]  = CC_equal,
	[ARC_CC_NE]  = CC_unequal,
	[ARC_CC_SET] = CC_unequal
};

/* Can the jump from "curr_off" to "targ_off" actually happen? */
bool check_jmp_32(u32 curr_off, u32 targ_off, u8 cond)
{
	u8 addendum;
	s32 disp;

	if (cond >= ARC_CC_LAST)
		return false;

	/*
	 * The unconditional jump happens immediately, while the rest
	 * are either preceded by a "cmp" or "tst" instruction.
	 */
	addendum = (cond == ARC_CC_AL) ? 0 : INSN_len_normal;
	disp = get_displacement(curr_off + addendum, targ_off);

	if (cond == ARC_CC_AL)
		return is_valid_far_disp(disp);
	else
		return is_valid_near_disp(disp);
}

/*
 * The JITed code for 32-bit (conditional) branches:
 *
 * ARC_CC_AL  @target
 *   b @jit_targ_addr
 *
 * ARC_CC_SET rd, rs, @target
 *   tst rd, rs
 *   bnz @jit_targ_addr
 *
 * ARC_CC_xx  rd, rs, @target
 *   cmp rd, rs
 *   b<cc> @jit_targ_addr            # cc = arcv2_32_jmps[xx]
 */
u8 gen_jmp_32(u8 *buf, u8 rd, u8 rs, u8 cond, u32 curr_off, u32 targ_off)
{
	s32 disp;
	u8 len = 0;

	/*
	 * Although this must have already been checked by "check_jmp_32()",
	 * we're not going to risk accessing "arcv2_32_jmps" array without
	 * the boundary check.
	 */
	if (cond >= ARC_CC_LAST) {
#ifdef ARC_BPF_JIT_DEBUG
		pr_err("32-bit jump condition is not known.");
		BUG();
#endif
		return 0;
	}

	/* If there is a "condition", issue the "cmp" or "tst" first. */
	if (cond != ARC_CC_AL) {
		if (cond == ARC_CC_SET)
			len = tst_r32(buf, rd, rs);
		else
			len = cmp_r32(buf, rd, rs);
		/*
		 * The issued instruction affects the "disp"lacement as
		 * it alters the "curr_off" by its "len"gth. The "curr_off"
		 * should always point to the jump instruction.
		 */
		disp = get_displacement(curr_off + len, targ_off);
		len += arc_bcc(BUF(buf, len), arcv2_32_jmps[cond], disp);
	} else {
		/* The straight forward unconditional jump. */
		disp = get_displacement(curr_off, targ_off);
		len = arc_b(buf, disp);
	}

	return len;
}

/*
 * Generate code for functions calls. There can be two types of calls:
 *
 * - Calling another BPF function
 * - Calling an in-kernel function which is compiled by ARC gcc
 *
 * In the later case, we must comply to ARCv2 ABI and handle arguments
 * and return values accordingly.
 */
u8 gen_func_call(u8 *buf, ARC_ADDR func_addr, bool external_func)
{
	u8 len = 0;

	/*
	 * In case of an in-kernel function call, always push the 5th
	 * argument onto the stack, because that's where the ABI dictates
	 * it should be found. If the callee doesn't really use it, no harm
	 * is done. The stack is readjusted either way after the call.
	 */
	if (external_func)
		len += push_r64(BUF(buf, len), BPF_REG_5);

	len += jump_and_link(BUF(buf, len), func_addr);

	if (external_func)
		len += arc_add_i(BUF(buf, len), ARC_R_SP, ARC_R_SP, ARG5_SIZE);

	return len;
}