// SPDX-License-Identifier: GPL-2.0-only
/*
 * Just-In-Time compiler for eBPF bytecode on MIPS.
 * Implementation of JIT functions common to 32-bit and 64-bit CPUs.
 *
 * Copyright (c) 2021 Anyfi Networks AB.
 * Author: Johan Almbladh <johan.almbladh@gmail.com>
 *
 * Based on code and ideas from
 * Copyright (c) 2017 Cavium, Inc.
 * Copyright (c) 2017 Shubham Bansal <illusionist.neo@gmail.com>
 * Copyright (c) 2011 Mircea Gherzan <mgherzan@gmail.com>
 */

/*
 * Code overview
 * =============
 *
 * - bpf_jit_comp.h
 *   Common definitions and utilities.
 *
 * - bpf_jit_comp.c
 *   Implementation of JIT top-level logic and exported JIT API functions.
 *   Implementation of internal operations shared by 32-bit and 64-bit code.
 *   JMP and ALU JIT control code, register control code, shared ALU and
 *   JMP/JMP32 JIT operations.
 *
 * - bpf_jit_comp32.c
 *   Implementation of functions to JIT prologue, epilogue and a single eBPF
 *   instruction for 32-bit MIPS CPUs. The functions use shared operations
 *   where possible, and implement the rest for 32-bit MIPS such as ALU64
 *   operations.
 *
 * - bpf_jit_comp64.c
 *   Ditto, for 64-bit MIPS CPUs.
 *
 * Zero and sign extension
 * ========================
 * 32-bit MIPS instructions on 64-bit MIPS registers use sign extension,
 * but the eBPF instruction set mandates zero extension. We let the verifier
 * insert explicit zero-extensions after 32-bit ALU operations, both for
 * 32-bit and 64-bit MIPS JITs. Conditional JMP32 operations on 64-bit MIPs
 * are JITed with sign extensions inserted when so expected.
 *
 * ALU operations
 * ==============
 * ALU operations on 32/64-bit MIPS and ALU64 operations on 64-bit MIPS are
 * JITed in the following steps. ALU64 operations on 32-bit MIPS are more
 * complicated and therefore only processed by special implementations in
 * step (3).
 *
 * 1) valid_alu_i:
 *    Determine if an immediate operation can be emitted as such, or if
 *    we must fall back to the register version.
 *
 * 2) rewrite_alu_i:
 *    Convert BPF operation and immediate value to a canonical form for
 *    JITing. In some degenerate cases this form may be a no-op.
 *
 * 3) emit_alu_{i,i64,r,64}:
 *    Emit instructions for an ALU or ALU64 immediate or register operation.
 *
 * JMP operations
 * ==============
 * JMP and JMP32 operations require an JIT instruction offset table for
 * translating the jump offset. This table is computed by dry-running the
 * JIT without actually emitting anything. However, the computed PC-relative
 * offset may overflow the 18-bit offset field width of the native MIPS
 * branch instruction. In such cases, the long jump is converted into the
 * following sequence.
 *
 *    <branch> !<cond> +2    Inverted PC-relative branch
 *    nop                    Delay slot
 *    j <offset>             Unconditional absolute long jump
 *    nop                    Delay slot
 *
 * Since this converted sequence alters the offset table, all offsets must
 * be re-calculated. This may in turn trigger new branch conversions, so
 * the process is repeated until no further changes are made. Normally it
 * completes in 1-2 iterations. If JIT_MAX_ITERATIONS should reached, we
 * fall back to converting every remaining jump operation. The branch
 * conversion is independent of how the JMP or JMP32 condition is JITed.
 *
 * JMP32 and JMP operations are JITed as follows.
 *
 * 1) setup_jmp_{i,r}:
 *    Convert jump conditional and offset into a form that can be JITed.
 *    This form may be a no-op, a canonical form, or an inverted PC-relative
 *    jump if branch conversion is necessary.
 *
 * 2) valid_jmp_i:
 *    Determine if an immediate operations can be emitted as such, or if
 *    we must fall back to the register version. Applies to JMP32 for 32-bit
 *    MIPS, and both JMP and JMP32 for 64-bit MIPS.
 *
 * 3) emit_jmp_{i,i64,r,r64}:
 *    Emit instructions for an JMP or JMP32 immediate or register operation.
 *
 * 4) finish_jmp_{i,r}:
 *    Emit any instructions needed to finish the jump. This includes a nop
 *    for the delay slot if a branch was emitted, and a long absolute jump
 *    if the branch was converted.
 */

#include <linux/limits.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/filter.h>
#include <linux/bpf.h>
#include <linux/slab.h>
#include <asm/bitops.h>
#include <asm/cacheflush.h>
#include <asm/cpu-features.h>
#include <asm/isa-rev.h>
#include <asm/uasm.h>

#include "bpf_jit_comp.h"

/* Convenience macros for descriptor access */
#define CONVERTED(desc) ((desc) & JIT_DESC_CONVERT)
#define INDEX(desc)     ((desc) & ~JIT_DESC_CONVERT)

/*
 * Push registers on the stack, starting at a given depth from the stack
 * pointer and increasing. The next depth to be written is returned.
 */
int push_regs(struct jit_context *ctx, u32 mask, u32 excl, int depth)
{
        int reg;

        for (reg = 0; reg < BITS_PER_BYTE * sizeof(mask); reg++)
                if (mask & BIT(reg)) {
                        if ((excl & BIT(reg)) == 0) {
                                if (sizeof(long) == 4)
                                        emit(ctx, sw, reg, depth, MIPS_R_SP);
                                else /* sizeof(long) == 8 */
                                        emit(ctx, sd, reg, depth, MIPS_R_SP);
                        }
                        depth += sizeof(long);
                }

        ctx->stack_used = max((int)ctx->stack_used, depth);
        return depth;
}

/*
 * Pop registers from the stack, starting at a given depth from the stack
 * pointer and increasing. The next depth to be read is returned.
 */
int pop_regs(struct jit_context *ctx, u32 mask, u32 excl, int depth)
{
        int reg;

        for (reg = 0; reg < BITS_PER_BYTE * sizeof(mask); reg++)
                if (mask & BIT(reg)) {
                        if ((excl & BIT(reg)) == 0) {
                                if (sizeof(long) == 4)
                                        emit(ctx, lw, reg, depth, MIPS_R_SP);
                                else /* sizeof(long) == 8 */
                                        emit(ctx, ld, reg, depth, MIPS_R_SP);
                        }
                        depth += sizeof(long);
                }

        return depth;
}

/* Compute the 28-bit jump target address from a BPF program location */
int get_target(struct jit_context *ctx, u32 loc)
{
        u32 index = INDEX(ctx->descriptors[loc]);
        unsigned long pc = (unsigned long)&ctx->target[ctx->jit_index];
        unsigned long addr = (unsigned long)&ctx->target[index];

        if (!ctx->target)
                return 0;

        if ((addr ^ pc) & ~MIPS_JMP_MASK)
                return -1;

        return addr & MIPS_JMP_MASK;
}

/* Compute the PC-relative offset to relative BPF program offset */
int get_offset(const struct jit_context *ctx, int off)
{
        return (INDEX(ctx->descriptors[ctx->bpf_index + off]) -
                ctx->jit_index - 1) * sizeof(u32);
}

/* dst = imm (register width) */
void emit_mov_i(struct jit_context *ctx, u8 dst, s32 imm)
{
        if (imm >= -0x8000 && imm <= 0x7fff) {
                emit(ctx, addiu, dst, MIPS_R_ZERO, imm);
        } else {
                emit(ctx, lui, dst, (s16)((u32)imm >> 16));
                emit(ctx, ori, dst, dst, (u16)(imm & 0xffff));
        }
        clobber_reg(ctx, dst);
}

/* dst = src (register width) */
void emit_mov_r(struct jit_context *ctx, u8 dst, u8 src)
{
        emit(ctx, ori, dst, src, 0);
        clobber_reg(ctx, dst);
}

/* Validate ALU immediate range */
bool valid_alu_i(u8 op, s32 imm)
{
        switch (BPF_OP(op)) {
        case BPF_NEG:
        case BPF_LSH:
        case BPF_RSH:
        case BPF_ARSH:
                /* All legal eBPF values are valid */
                return true;
        case BPF_ADD:
                /* imm must be 16 bits */
                return imm >= -0x8000 && imm <= 0x7fff;
        case BPF_SUB:
                /* -imm must be 16 bits */
                return imm >= -0x7fff && imm <= 0x8000;
        case BPF_AND:
        case BPF_OR:
        case BPF_XOR:
                /* imm must be 16 bits unsigned */
                return imm >= 0 && imm <= 0xffff;
        case BPF_MUL:
                /* imm must be zero or a positive power of two */
                return imm == 0 || (imm > 0 && is_power_of_2(imm));
        case BPF_DIV:
        case BPF_MOD:
                /* imm must be an 17-bit power of two */
                return (u32)imm <= 0x10000 && is_power_of_2((u32)imm);
        }
        return false;
}

/* Rewrite ALU immediate operation */
bool rewrite_alu_i(u8 op, s32 imm, u8 *alu, s32 *val)
{
        bool act = true;

        switch (BPF_OP(op)) {
        case BPF_LSH:
        case BPF_RSH:
        case BPF_ARSH:
        case BPF_ADD:
        case BPF_SUB:
        case BPF_OR:
        case BPF_XOR:
                /* imm == 0 is a no-op */
                act = imm != 0;
                break;
        case BPF_MUL:
                if (imm == 1) {
                        /* dst * 1 is a no-op */
                        act = false;
                } else if (imm == 0) {
                        /* dst * 0 is dst & 0 */
                        op = BPF_AND;
                } else {
                        /* dst * (1 << n) is dst << n */
                        op = BPF_LSH;
                        imm = ilog2(abs(imm));
                }
                break;
        case BPF_DIV:
                if (imm == 1) {
                        /* dst / 1 is a no-op */
                        act = false;
                } else {
                        /* dst / (1 << n) is dst >> n */
                        op = BPF_RSH;
                        imm = ilog2(imm);
                }
                break;
        case BPF_MOD:
                /* dst % (1 << n) is dst & ((1 << n) - 1) */
                op = BPF_AND;
                imm--;
                break;
        }

        *alu = op;
        *val = imm;
        return act;
}

/* ALU immediate operation (32-bit) */
void emit_alu_i(struct jit_context *ctx, u8 dst, s32 imm, u8 op)
{
        switch (BPF_OP(op)) {
        /* dst = -dst */
        case BPF_NEG:
                emit(ctx, subu, dst, MIPS_R_ZERO, dst);
                break;
        /* dst = dst & imm */
        case BPF_AND:
                emit(ctx, andi, dst, dst, (u16)imm);
                break;
        /* dst = dst | imm */
        case BPF_OR:
                emit(ctx, ori, dst, dst, (u16)imm);
                break;
        /* dst = dst ^ imm */
        case BPF_XOR:
                emit(ctx, xori, dst, dst, (u16)imm);
                break;
        /* dst = dst << imm */
        case BPF_LSH:
                emit(ctx, sll, dst, dst, imm);
                break;
        /* dst = dst >> imm */
        case BPF_RSH:
                emit(ctx, srl, dst, dst, imm);
                break;
        /* dst = dst >> imm (arithmetic) */
        case BPF_ARSH:
                emit(ctx, sra, dst, dst, imm);
                break;
        /* dst = dst + imm */
        case BPF_ADD:
                emit(ctx, addiu, dst, dst, imm);
                break;
        /* dst = dst - imm */
        case BPF_SUB:
                emit(ctx, addiu, dst, dst, -imm);
                break;
        }
        clobber_reg(ctx, dst);
}

/* ALU register operation (32-bit) */
void emit_alu_r(struct jit_context *ctx, u8 dst, u8 src, u8 op)
{
        switch (BPF_OP(op)) {
        /* dst = dst & src */
        case BPF_AND:
                emit(ctx, and, dst, dst, src);
                break;
        /* dst = dst | src */
        case BPF_OR:
                emit(ctx, or, dst, dst, src);
                break;
        /* dst = dst ^ src */
        case BPF_XOR:
                emit(ctx, xor, dst, dst, src);
                break;
        /* dst = dst << src */
        case BPF_LSH:
                emit(ctx, sllv, dst, dst, src);
                break;
        /* dst = dst >> src */
        case BPF_RSH:
                emit(ctx, srlv, dst, dst, src);
                break;
        /* dst = dst >> src (arithmetic) */
        case BPF_ARSH:
                emit(ctx, srav, dst, dst, src);
                break;
        /* dst = dst + src */
        case BPF_ADD:
                emit(ctx, addu, dst, dst, src);
                break;
        /* dst = dst - src */
        case BPF_SUB:
                emit(ctx, subu, dst, dst, src);
                break;
        /* dst = dst * src */
        case BPF_MUL:
                if (cpu_has_mips32r1 || cpu_has_mips32r6) {
                        emit(ctx, mul, dst, dst, src);
                } else {
                        emit(ctx, multu, dst, src);
                        emit(ctx, mflo, dst);
                }
                break;
        /* dst = dst / src */
        case BPF_DIV:
                if (cpu_has_mips32r6) {
                        emit(ctx, divu_r6, dst, dst, src);
                } else {
                        emit(ctx, divu, dst, src);
                        emit(ctx, mflo, dst);
                }
                break;
        /* dst = dst % src */
        case BPF_MOD:
                if (cpu_has_mips32r6) {
                        emit(ctx, modu, dst, dst, src);
                } else {
                        emit(ctx, divu, dst, src);
                        emit(ctx, mfhi, dst);
                }
                break;
        }
        clobber_reg(ctx, dst);
}

/* Atomic read-modify-write (32-bit) */
void emit_atomic_r(struct jit_context *ctx, u8 dst, u8 src, s16 off, u8 code)
{
        LLSC_sync(ctx);
        emit(ctx, ll, MIPS_R_T9, off, dst);
        switch (code) {
        case BPF_ADD:
        case BPF_ADD | BPF_FETCH:
                emit(ctx, addu, MIPS_R_T8, MIPS_R_T9, src);
                break;
        case BPF_AND:
        case BPF_AND | BPF_FETCH:
                emit(ctx, and, MIPS_R_T8, MIPS_R_T9, src);
                break;
        case BPF_OR:
        case BPF_OR | BPF_FETCH:
                emit(ctx, or, MIPS_R_T8, MIPS_R_T9, src);
                break;
        case BPF_XOR:
        case BPF_XOR | BPF_FETCH:
                emit(ctx, xor, MIPS_R_T8, MIPS_R_T9, src);
                break;
        case BPF_XCHG:
                emit(ctx, move, MIPS_R_T8, src);
                break;
        }
        emit(ctx, sc, MIPS_R_T8, off, dst);
        emit(ctx, LLSC_beqz, MIPS_R_T8, -16 - LLSC_offset);
        emit(ctx, nop); /* Delay slot */

        if (code & BPF_FETCH) {
                emit(ctx, move, src, MIPS_R_T9);
                clobber_reg(ctx, src);
        }
}

/* Atomic compare-and-exchange (32-bit) */
void emit_cmpxchg_r(struct jit_context *ctx, u8 dst, u8 src, u8 res, s16 off)
{
        LLSC_sync(ctx);
        emit(ctx, ll, MIPS_R_T9, off, dst);
        emit(ctx, bne, MIPS_R_T9, res, 12);
        emit(ctx, move, MIPS_R_T8, src);     /* Delay slot */
        emit(ctx, sc, MIPS_R_T8, off, dst);
        emit(ctx, LLSC_beqz, MIPS_R_T8, -20 - LLSC_offset);
        emit(ctx, move, res, MIPS_R_T9);     /* Delay slot */
        clobber_reg(ctx, res);
}

/* Swap bytes and truncate a register word or half word */
void emit_bswap_r(struct jit_context *ctx, u8 dst, u32 width)
{
        u8 tmp = MIPS_R_T8;
        u8 msk = MIPS_R_T9;

        switch (width) {
        /* Swap bytes in a word */
        case 32:
                if (cpu_has_mips32r2 || cpu_has_mips32r6) {
                        emit(ctx, wsbh, dst, dst);
                        emit(ctx, rotr, dst, dst, 16);
                } else {
                        emit(ctx, sll, tmp, dst, 16);    /* tmp  = dst << 16 */
                        emit(ctx, srl, dst, dst, 16);    /* dst = dst >> 16  */
                        emit(ctx, or, dst, dst, tmp);    /* dst = dst | tmp  */

                        emit(ctx, lui, msk, 0xff);       /* msk = 0x00ff0000 */
                        emit(ctx, ori, msk, msk, 0xff);  /* msk = msk | 0xff */

                        emit(ctx, and, tmp, dst, msk);   /* tmp = dst & msk  */
                        emit(ctx, sll, tmp, tmp, 8);     /* tmp = tmp << 8   */
                        emit(ctx, srl, dst, dst, 8);     /* dst = dst >> 8   */
                        emit(ctx, and, dst, dst, msk);   /* dst = dst & msk  */
                        emit(ctx, or, dst, dst, tmp);    /* reg = dst | tmp  */
                }
                break;
        /* Swap bytes in a half word */
        case 16:
                if (cpu_has_mips32r2 || cpu_has_mips32r6) {
                        emit(ctx, wsbh, dst, dst);
                        emit(ctx, andi, dst, dst, 0xffff);
                } else {
                        emit(ctx, andi, tmp, dst, 0xff00); /* t = d & 0xff00 */
                        emit(ctx, srl, tmp, tmp, 8);       /* t = t >> 8     */
                        emit(ctx, andi, dst, dst, 0x00ff); /* d = d & 0x00ff */
                        emit(ctx, sll, dst, dst, 8);       /* d = d << 8     */
                        emit(ctx, or,  dst, dst, tmp);     /* d = d | t      */
                }
                break;
        }
        clobber_reg(ctx, dst);
}

/* Validate jump immediate range */
bool valid_jmp_i(u8 op, s32 imm)
{
        switch (op) {
        case JIT_JNOP:
                /* Immediate value not used */
                return true;
        case BPF_JEQ:
        case BPF_JNE:
                /* No immediate operation */
                return false;
        case BPF_JSET:
        case JIT_JNSET:
                /* imm must be 16 bits unsigned */
                return imm >= 0 && imm <= 0xffff;
        case BPF_JGE:
        case BPF_JLT:
        case BPF_JSGE:
        case BPF_JSLT:
                /* imm must be 16 bits */
                return imm >= -0x8000 && imm <= 0x7fff;
        case BPF_JGT:
        case BPF_JLE:
        case BPF_JSGT:
        case BPF_JSLE:
                /* imm + 1 must be 16 bits */
                return imm >= -0x8001 && imm <= 0x7ffe;
        }
        return false;
}

/* Invert a conditional jump operation */
static u8 invert_jmp(u8 op)
{
        switch (op) {
        case BPF_JA: return JIT_JNOP;
        case BPF_JEQ: return BPF_JNE;
        case BPF_JNE: return BPF_JEQ;
        case BPF_JSET: return JIT_JNSET;
        case BPF_JGT: return BPF_JLE;
        case BPF_JGE: return BPF_JLT;
        case BPF_JLT: return BPF_JGE;
        case BPF_JLE: return BPF_JGT;
        case BPF_JSGT: return BPF_JSLE;
        case BPF_JSGE: return BPF_JSLT;
        case BPF_JSLT: return BPF_JSGE;
        case BPF_JSLE: return BPF_JSGT;
        }
        return 0;
}

/* Prepare a PC-relative jump operation */
static void setup_jmp(struct jit_context *ctx, u8 bpf_op,
                      s16 bpf_off, u8 *jit_op, s32 *jit_off)
{
        u32 *descp = &ctx->descriptors[ctx->bpf_index];
        int op = bpf_op;
        int offset = 0;

        /* Do not compute offsets on the first pass */
        if (INDEX(*descp) == 0)
                goto done;

        /* Skip jumps never taken */
        if (bpf_op == JIT_JNOP)
                goto done;

        /* Convert jumps always taken */
        if (bpf_op == BPF_JA)
                *descp |= JIT_DESC_CONVERT;

        /*
         * Current ctx->jit_index points to the start of the branch preamble.
         * Since the preamble differs among different branch conditionals,
         * the current index cannot be used to compute the branch offset.
         * Instead, we use the offset table value for the next instruction,
         * which gives the index immediately after the branch delay slot.
         */
        if (!CONVERTED(*descp)) {
                int target = ctx->bpf_index + bpf_off + 1;
                int origin = ctx->bpf_index + 1;

                offset = (INDEX(ctx->descriptors[target]) -
                          INDEX(ctx->descriptors[origin]) + 1) * sizeof(u32);
        }

        /*
         * The PC-relative branch offset field on MIPS is 18 bits signed,
         * so if the computed offset is larger than this we generate a an
         * absolute jump that we skip with an inverted conditional branch.
         */
        if (CONVERTED(*descp) || offset < -0x20000 || offset > 0x1ffff) {
                offset = 3 * sizeof(u32);
                op = invert_jmp(bpf_op);
                ctx->changes += !CONVERTED(*descp);
                *descp |= JIT_DESC_CONVERT;
        }

done:
        *jit_off = offset;
        *jit_op = op;
}

/* Prepare a PC-relative jump operation with immediate conditional */
void setup_jmp_i(struct jit_context *ctx, s32 imm, u8 width,
                 u8 bpf_op, s16 bpf_off, u8 *jit_op, s32 *jit_off)
{
        bool always = false;
        bool never = false;

        switch (bpf_op) {
        case BPF_JEQ:
        case BPF_JNE:
                break;
        case BPF_JSET:
        case BPF_JLT:
                never = imm == 0;
                break;
        case BPF_JGE:
                always = imm == 0;
                break;
        case BPF_JGT:
                never = (u32)imm == U32_MAX;
                break;
        case BPF_JLE:
                always = (u32)imm == U32_MAX;
                break;
        case BPF_JSGT:
                never = imm == S32_MAX && width == 32;
                break;
        case BPF_JSGE:
                always = imm == S32_MIN && width == 32;
                break;
        case BPF_JSLT:
                never = imm == S32_MIN && width == 32;
                break;
        case BPF_JSLE:
                always = imm == S32_MAX && width == 32;
                break;
        }

        if (never)
                bpf_op = JIT_JNOP;
        if (always)
                bpf_op = BPF_JA;
        setup_jmp(ctx, bpf_op, bpf_off, jit_op, jit_off);
}

/* Prepare a PC-relative jump operation with register conditional */
void setup_jmp_r(struct jit_context *ctx, bool same_reg,
                 u8 bpf_op, s16 bpf_off, u8 *jit_op, s32 *jit_off)
{
        switch (bpf_op) {
        case BPF_JSET:
                break;
        case BPF_JEQ:
        case BPF_JGE:
        case BPF_JLE:
        case BPF_JSGE:
        case BPF_JSLE:
                if (same_reg)
                        bpf_op = BPF_JA;
                break;
        case BPF_JNE:
        case BPF_JLT:
        case BPF_JGT:
        case BPF_JSGT:
        case BPF_JSLT:
                if (same_reg)
                        bpf_op = JIT_JNOP;
                break;
        }
        setup_jmp(ctx, bpf_op, bpf_off, jit_op, jit_off);
}

/* Finish a PC-relative jump operation */
int finish_jmp(struct jit_context *ctx, u8 jit_op, s16 bpf_off)
{
        /* Emit conditional branch delay slot */
        if (jit_op != JIT_JNOP)
                emit(ctx, nop);
        /*
         * Emit an absolute long jump with delay slot,
         * if the PC-relative branch was converted.
         */
        if (CONVERTED(ctx->descriptors[ctx->bpf_index])) {
                int target = get_target(ctx, ctx->bpf_index + bpf_off + 1);

                if (target < 0)
                        return -1;
                emit(ctx, j, target);
                emit(ctx, nop);
        }
        return 0;
}

/* Jump immediate (32-bit) */
void emit_jmp_i(struct jit_context *ctx, u8 dst, s32 imm, s32 off, u8 op)
{
        switch (op) {
        /* No-op, used internally for branch optimization */
        case JIT_JNOP:
                break;
        /* PC += off if dst & imm */
        case BPF_JSET:
                emit(ctx, andi, MIPS_R_T9, dst, (u16)imm);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        /* PC += off if (dst & imm) == 0 (not in BPF, used for long jumps) */
        case JIT_JNSET:
                emit(ctx, andi, MIPS_R_T9, dst, (u16)imm);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        /* PC += off if dst > imm */
        case BPF_JGT:
                emit(ctx, sltiu, MIPS_R_T9, dst, imm + 1);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        /* PC += off if dst >= imm */
        case BPF_JGE:
                emit(ctx, sltiu, MIPS_R_T9, dst, imm);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        /* PC += off if dst < imm */
        case BPF_JLT:
                emit(ctx, sltiu, MIPS_R_T9, dst, imm);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        /* PC += off if dst <= imm */
        case BPF_JLE:
                emit(ctx, sltiu, MIPS_R_T9, dst, imm + 1);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        /* PC += off if dst > imm (signed) */
        case BPF_JSGT:
                emit(ctx, slti, MIPS_R_T9, dst, imm + 1);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        /* PC += off if dst >= imm (signed) */
        case BPF_JSGE:
                emit(ctx, slti, MIPS_R_T9, dst, imm);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        /* PC += off if dst < imm (signed) */
        case BPF_JSLT:
                emit(ctx, slti, MIPS_R_T9, dst, imm);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        /* PC += off if dst <= imm (signed) */
        case BPF_JSLE:
                emit(ctx, slti, MIPS_R_T9, dst, imm + 1);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        }
}

/* Jump register (32-bit) */
void emit_jmp_r(struct jit_context *ctx, u8 dst, u8 src, s32 off, u8 op)
{
        switch (op) {
        /* No-op, used internally for branch optimization */
        case JIT_JNOP:
                break;
        /* PC += off if dst == src */
        case BPF_JEQ:
                emit(ctx, beq, dst, src, off);
                break;
        /* PC += off if dst != src */
        case BPF_JNE:
                emit(ctx, bne, dst, src, off);
                break;
        /* PC += off if dst & src */
        case BPF_JSET:
                emit(ctx, and, MIPS_R_T9, dst, src);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        /* PC += off if (dst & imm) == 0 (not in BPF, used for long jumps) */
        case JIT_JNSET:
                emit(ctx, and, MIPS_R_T9, dst, src);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        /* PC += off if dst > src */
        case BPF_JGT:
                emit(ctx, sltu, MIPS_R_T9, src, dst);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        /* PC += off if dst >= src */
        case BPF_JGE:
                emit(ctx, sltu, MIPS_R_T9, dst, src);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        /* PC += off if dst < src */
        case BPF_JLT:
                emit(ctx, sltu, MIPS_R_T9, dst, src);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        /* PC += off if dst <= src */
        case BPF_JLE:
                emit(ctx, sltu, MIPS_R_T9, src, dst);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        /* PC += off if dst > src (signed) */
        case BPF_JSGT:
                emit(ctx, slt, MIPS_R_T9, src, dst);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        /* PC += off if dst >= src (signed) */
        case BPF_JSGE:
                emit(ctx, slt, MIPS_R_T9, dst, src);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        /* PC += off if dst < src (signed) */
        case BPF_JSLT:
                emit(ctx, slt, MIPS_R_T9, dst, src);
                emit(ctx, bnez, MIPS_R_T9, off);
                break;
        /* PC += off if dst <= src (signed) */
        case BPF_JSLE:
                emit(ctx, slt, MIPS_R_T9, src, dst);
                emit(ctx, beqz, MIPS_R_T9, off);
                break;
        }
}

/* Jump always */
int emit_ja(struct jit_context *ctx, s16 off)
{
        int target = get_target(ctx, ctx->bpf_index + off + 1);

        if (target < 0)
                return -1;
        emit(ctx, j, target);
        emit(ctx, nop);
        return 0;
}

/* Jump to epilogue */
int emit_exit(struct jit_context *ctx)
{
        int target = get_target(ctx, ctx->program->len);

        if (target < 0)
                return -1;
        emit(ctx, j, target);
        emit(ctx, nop);
        return 0;
}

/* Build the program body from eBPF bytecode */
static int build_body(struct jit_context *ctx)
{
        const struct bpf_prog *prog = ctx->program;
        unsigned int i;

        ctx->stack_used = 0;
        for (i = 0; i < prog->len; i++) {
                const struct bpf_insn *insn = &prog->insnsi[i];
                u32 *descp = &ctx->descriptors[i];
                int ret;

                access_reg(ctx, insn->src_reg);
                access_reg(ctx, insn->dst_reg);

                ctx->bpf_index = i;
                if (ctx->target == NULL) {
                        ctx->changes += INDEX(*descp) != ctx->jit_index;
                        *descp &= JIT_DESC_CONVERT;
                        *descp |= ctx->jit_index;
                }

                ret = build_insn(insn, ctx);
                if (ret < 0)
                        return ret;

                if (ret > 0) {
                        i++;
                        if (ctx->target == NULL)
                                descp[1] = ctx->jit_index;
                }
        }

        /* Store the end offset, where the epilogue begins */
        ctx->descriptors[prog->len] = ctx->jit_index;
        return 0;
}

/* Set the branch conversion flag on all instructions */
static void set_convert_flag(struct jit_context *ctx, bool enable)
{
        const struct bpf_prog *prog = ctx->program;
        u32 flag = enable ? JIT_DESC_CONVERT : 0;
        unsigned int i;

        for (i = 0; i <= prog->len; i++)
                ctx->descriptors[i] = INDEX(ctx->descriptors[i]) | flag;
}

static void jit_fill_hole(void *area, unsigned int size)
{
        u32 *p;

        /* We are guaranteed to have aligned memory. */
        for (p = area; size >= sizeof(u32); size -= sizeof(u32))
                uasm_i_break(&p, BRK_BUG); /* Increments p */
}

bool bpf_jit_needs_zext(void)
{
        return true;
}

struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
{
        struct bpf_prog *tmp, *orig_prog = prog;
        struct bpf_binary_header *header = NULL;
        struct jit_context ctx;
        bool tmp_blinded = false;
        unsigned int tmp_idx;
        unsigned int image_size;
        u8 *image_ptr;
        int tries;

        /*
         * If BPF JIT was not enabled then we must fall back to
         * the interpreter.
         */
        if (!prog->jit_requested)
                return orig_prog;
        /*
         * If constant blinding was enabled and we failed during blinding
         * then we must fall back to the interpreter. Otherwise, we save
         * the new JITed code.
         */
        tmp = bpf_jit_blind_constants(prog);
        if (IS_ERR(tmp))
                return orig_prog;
        if (tmp != prog) {
                tmp_blinded = true;
                prog = tmp;
        }

        memset(&ctx, 0, sizeof(ctx));
        ctx.program = prog;

        /*
         * Not able to allocate memory for descriptors[], then
         * we must fall back to the interpreter
         */
        ctx.descriptors = kcalloc(prog->len + 1, sizeof(*ctx.descriptors),
                                  GFP_KERNEL);
        if (ctx.descriptors == NULL)
                goto out_err;

        /* First pass discovers used resources */
        if (build_body(&ctx) < 0)
                goto out_err;
        /*
         * Second pass computes instruction offsets.
         * If any PC-relative branches are out of range, a sequence of
         * a PC-relative branch + a jump is generated, and we have to
         * try again from the beginning to generate the new offsets.
         * This is done until no additional conversions are necessary.
         * The last two iterations are done with all branches being
         * converted, to guarantee offset table convergence within a
         * fixed number of iterations.
         */
        ctx.jit_index = 0;
        build_prologue(&ctx);
        tmp_idx = ctx.jit_index;

        tries = JIT_MAX_ITERATIONS;
        do {
                ctx.jit_index = tmp_idx;
                ctx.changes = 0;
                if (tries == 2)
                        set_convert_flag(&ctx, true);
                if (build_body(&ctx) < 0)
                        goto out_err;
        } while (ctx.changes > 0 && --tries > 0);

        if (WARN_ONCE(ctx.changes > 0, "JIT offsets failed to converge"))
                goto out_err;

        build_epilogue(&ctx, MIPS_R_RA);

        /* Now we know the size of the structure to make */
        image_size = sizeof(u32) * ctx.jit_index;
        header = bpf_jit_binary_alloc(image_size, &image_ptr,
                                      sizeof(u32), jit_fill_hole);
        /*
         * Not able to allocate memory for the structure then
         * we must fall back to the interpretation
         */
        if (header == NULL)
                goto out_err;

        /* Actual pass to generate final JIT code */
        ctx.target = (u32 *)image_ptr;
        ctx.jit_index = 0;

        /*
         * If building the JITed code fails somehow,
         * we fall back to the interpretation.
         */

        build_prologue(&ctx);
        if (build_body(&ctx) < 0)
                goto out_err;
        build_epilogue(&ctx, MIPS_R_RA);

        /* Populate line info meta data */
        set_convert_flag(&ctx, false);
        bpf_prog_fill_jited_linfo(prog, &ctx.descriptors[1]);

        /* Set as read-only exec and flush instruction cache */
        bpf_jit_binary_lock_ro(header);
        flush_icache_range((unsigned long)header,
                           (unsigned long)&ctx.target[ctx.jit_index]);

        if (bpf_jit_enable > 1)
                bpf_jit_dump(prog->len, image_size, 2, ctx.target);

        prog->bpf_func = (void *)ctx.target;
        prog->jited = 1;
        prog->jited_len = image_size;

out:
        if (tmp_blinded)
                bpf_jit_prog_release_other(prog, prog == orig_prog ?
                                           tmp : orig_prog);
        kfree(ctx.descriptors);
        return prog;

out_err:
        prog = orig_prog;
        if (header)
                bpf_jit_binary_free(header);
        goto out;
}