disassembler.c

/*
 * Copyright 2016, The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <stdint.h>
#include <stdio.h>

#include "apf.h"

// If "c" is of a signed type, generate a compile warning that gets promoted to an error.
// This makes bounds checking simpler because ">= 0" can be avoided. Otherwise adding
// superfluous ">= 0" with unsigned expressions generates compile warnings.
#define ENFORCE_UNSIGNED(c) ((c)==(uint32_t)(c))

static void print_opcode(const char* opcode) {
  printf("%-6s", opcode);
}

// Mapping from opcode number to opcode name.
static const char* opcode_names [] = {
    [LDB_OPCODE] = "ldb",
    [LDH_OPCODE] = "ldh",
    [LDW_OPCODE] = "ldw",
    [LDBX_OPCODE] = "ldbx",
    [LDHX_OPCODE] = "ldhx",
    [LDWX_OPCODE] = "ldwx",
    [ADD_OPCODE] = "add",
    [MUL_OPCODE] = "mul",
    [DIV_OPCODE] = "div",
    [AND_OPCODE] = "and",
    [OR_OPCODE] = "or",
    [SH_OPCODE] = "sh",
    [LI_OPCODE] = "li",
    [JMP_OPCODE] = "jmp",
    [JEQ_OPCODE] = "jeq",
    [JNE_OPCODE] = "jne",
    [JGT_OPCODE] = "jgt",
    [JLT_OPCODE] = "jlt",
    [JSET_OPCODE] = "jset",
    [JNEBS_OPCODE] = "jnebs",
    [LDDW_OPCODE] = "lddw",
    [STDW_OPCODE] = "stdw",
};

static void print_jump_target(uint32_t target, uint32_t program_len) {
    if (target == program_len) {
        printf("PASS");
    } else if (target == program_len + 1) {
        printf("DROP");
    } else {
        printf("%u", target);
    }
}

uint32_t apf_disassemble(const uint8_t* program, uint32_t program_len, uint32_t pc) {
    printf("%8u: ", pc);

    if (pc == program_len) {
        printf("PASS\n");
        return ++pc;
    }

    if (pc == program_len + 1) {
        printf("DROP\n");
        return ++pc;
    }

    const uint8_t bytecode = program[pc++];
    const uint32_t opcode = EXTRACT_OPCODE(bytecode);
#define PRINT_OPCODE() print_opcode(opcode_names[opcode])
    const uint32_t reg_num = EXTRACT_REGISTER(bytecode);
    // All instructions have immediate fields, so load them now.
    const uint32_t len_field = EXTRACT_IMM_LENGTH(bytecode);
    uint32_t imm = 0;
    int32_t signed_imm = 0;
    if (len_field != 0) {
        const uint32_t imm_len = 1 << (len_field - 1);
        for (uint32_t i = 0; i < imm_len && pc < program_len; i++)
            imm = (imm << 8) | program[pc++];
        // Sign extend imm into signed_imm.
        signed_imm = imm << ((4 - imm_len) * 8);
        signed_imm >>= (4 - imm_len) * 8;
    }
    switch (opcode) {
        case LDB_OPCODE:
        case LDH_OPCODE:
        case LDW_OPCODE:
            PRINT_OPCODE();
            printf("r%d, [%u]", reg_num, imm);
            break;
        case LDBX_OPCODE:
        case LDHX_OPCODE:
        case LDWX_OPCODE:
            PRINT_OPCODE();
            printf("r%d, [r1+%u]", reg_num, imm);
            break;
        case JMP_OPCODE:
            PRINT_OPCODE();
            print_jump_target(pc + imm, program_len);
            break;
        case JEQ_OPCODE:
        case JNE_OPCODE:
        case JGT_OPCODE:
        case JLT_OPCODE:
        case JSET_OPCODE:
        case JNEBS_OPCODE: {
            PRINT_OPCODE();
            printf("r0, ");
            // Load second immediate field.
            uint32_t cmp_imm = 0;
            if (reg_num == 1) {
                printf("r1, ");
            } else if (len_field == 0) {
                printf("0, ");
            } else {
                uint32_t cmp_imm_len = 1 << (len_field - 1);
                uint32_t i;
                for (i = 0; i < cmp_imm_len && pc < program_len; i++)
                    cmp_imm = (cmp_imm << 8) | program[pc++];
                printf("0x%x, ", cmp_imm);
            }
            if (opcode == JNEBS_OPCODE) {
                print_jump_target(pc + imm + cmp_imm, program_len);
                printf(", ");
                while (cmp_imm--)
                    printf("%02x", program[pc++]);
            } else {
                print_jump_target(pc + imm, program_len);
            }
            break;
        }
        case SH_OPCODE:
            PRINT_OPCODE();
            if (reg_num) {
                printf("r0, r1");
            } else {
                printf("r0, %d", signed_imm);
            }
            break;
        case ADD_OPCODE:
        case MUL_OPCODE:
        case DIV_OPCODE:
        case AND_OPCODE:
        case OR_OPCODE:
            PRINT_OPCODE();
            if (reg_num) {
                printf("r0, r1");
            } else {
                printf("r0, %u", imm);
            }
            break;
        case LI_OPCODE:
            PRINT_OPCODE();
            printf("r%d, %d", reg_num, signed_imm);
            break;
        case EXT_OPCODE:
            if (
// If LDM_EXT_OPCODE is 0 and imm is compared with it, a compiler error will result,
// instead just enforce that imm is unsigned (so it's always greater or equal to 0).
#if LDM_EXT_OPCODE == 0
                ENFORCE_UNSIGNED(imm) &&
#else
                imm >= LDM_EXT_OPCODE &&
#endif
                imm < (LDM_EXT_OPCODE + MEMORY_ITEMS)) {
                print_opcode("ldm");
                printf("r%d, m[%u]", reg_num, imm - LDM_EXT_OPCODE);
            } else if (imm >= STM_EXT_OPCODE && imm < (STM_EXT_OPCODE + MEMORY_ITEMS)) {
                print_opcode("stm");
                printf("r%d, m[%u]", reg_num, imm - STM_EXT_OPCODE);
            } else switch (imm) {
                case NOT_EXT_OPCODE:
                    print_opcode("not");
                    printf("r%d", reg_num);
                    break;
                case NEG_EXT_OPCODE:
                    print_opcode("neg");
                    printf("r%d", reg_num);
                    break;
                case SWAP_EXT_OPCODE:
                    print_opcode("swap");
                    break;
                case MOV_EXT_OPCODE:
                    print_opcode("mov");
                    printf("r%d, r%d", reg_num, reg_num ^ 1);
                    break;
                default:
                    printf("unknown_ext %u", imm);
                    break;
            }
            break;
        case LDDW_OPCODE:
        case STDW_OPCODE:
            PRINT_OPCODE();
            printf("r%u, [r%u+%d]", reg_num, reg_num ^ 1, signed_imm);
            break;

        // Unknown opcode
        default:
            printf("unknown %u", opcode);
            break;
    }
    printf("\n");
    return pc;
}