Answer of jit assignment https://karino2.github.io/c-lesson/casm_link_load.html

ps_jit_answer.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/mman.h>

#include "parser.h"
#include "test_util.h"

extern int eval(int r0, int r1, char *str);

/*
JIT
*/
int *binary_buf = NULL;

int* allocate_executable_buf(int size) {
    return (int*)mmap(0, size,
                 PROT_READ | PROT_WRITE | PROT_EXEC,
                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
}

void init_jit() {
    if(binary_buf == NULL) {
        binary_buf = allocate_executable_buf(1024);
    }
}

int binary_pos = 0;
void emit_word(int word) {
    binary_buf[binary_pos++] = word;
}

int asm_mov_reg(int reg_1st, int reg_2nd) {
    int oneword = 0xE1A00000;
    oneword += reg_1st << 12;
    oneword += reg_2nd;
    return oneword;    
}

void emit_mov_reg(int reg1, int reg2) {
    emit_word(asm_mov_reg(reg1, reg2));
}

int asm_mov_imm(int reg, int imm_value) {
    int oneword = 0xE3A00000;
    oneword += reg << 12;
    oneword += imm_value;    
    return oneword;
}

int asm_add_sub_common(int reg1, int dest_reg, int reg3, int baseword) {
    int oneword = baseword;
    oneword += reg1 << 16;
    oneword += dest_reg << 12;
    oneword += reg3;
    return oneword;
}

int asm_add_reg(int reg1, int dest_reg, int reg3) {
    // p29
    // 00I OPCODE = 000 0100 = 0000 100
    // OPCODE S = 100 0 = 8

    return asm_add_sub_common(reg1, dest_reg, reg3, 0xE0800000);
//    return asm_add_sub_common(reg1, dest_reg, reg3, 0xE2800000);
}

int asm_sub_reg(int reg1, int dest_reg, int reg3) {
//    return asm_add_sub_common(reg1, dest_reg, reg3, 0xE2400000);
    return asm_add_sub_common(reg1, dest_reg, reg3, 0xE0400000);
}


// mul r3, r1, r2
// r3 = r1*r2
int asm_mul_reg(int reg_dest, int reg1, int reg2) {
    // p40.
    // 0000
    // 00AS = 0000
    // rd XXXX rs 1001 rm
    // XXXX is ignored.
    int oneword = 0xe0000090;
    oneword += reg_dest<<16;
    oneword += reg1<<8;
    oneword += reg2;
    return oneword;
}


// always write back.
int asm_stmdb(int basereg, int registerlist) {
    int stmdb = 0xe9200000;
	stmdb += basereg << 16;
    stmdb += registerlist;
    return stmdb;
}

int asm_ldmia(int basereg, int registerlist) {
    int ldmia = 0xe8b00000;
	ldmia += basereg << 16;
    ldmia += registerlist;
    return ldmia;
}


// strdb r0, [r1]!
int asm_strdb(int basereg, int destreg) {
    // p42.
    // int oneword = 0xE5000000;
    //     int stmdb = 0xe9200000;
    // 01IP = 0101 = 5
    // UBWL = 0010 = 2
    int oneword = 0xE5200000;
    oneword += basereg << 16;
    oneword += destreg << 12;
    return oneword;
}

// ldria r0, [r1]!
int asm_ldria(int basereg, int srcreg) {
    //     int ldmia = 0xe8b00000;
    // 01IP = 0100 = 4
    // UBWL = 0011 = 3
    int oneword = 0xE4300000;
    oneword += basereg << 16;
    oneword += srcreg << 12;
    return oneword;
}

void emit_push_reg(int reg) {
    int word;
    // word = asm_strdb(reg, 13);
    word = asm_stmdb(13, 1<<reg);
    emit_word(word);
}

// mov r2, val
// ldr r2, [r13]!
void emit_push_val(int val) {
    int word;
    word = asm_mov_imm(2, val);
    emit_word(word);    
    emit_push_reg(2);
}


void emit_pop_reg(int reg) {
    int word;
//    word = asm_ldria(reg, 13);
    word = asm_ldmia(13, 1 << reg);
    emit_word(word);
}

/*
    ldria r3 [r13]!
    ldria r2 [r13]!
*/
void emit_pop_r2_r3() {
    emit_pop_reg(3);
    emit_pop_reg(2);
}

// add r2, r2, r3
void emit_add_r2_r3() {
    int word = asm_add_reg(2, 2, 3);
    emit_word(word);
}
void emit_sub_r2_r3() {
    int word = asm_sub_reg(2, 2, 3);
    emit_word(word);
}

void emit_mul_r2_r3() {
    int word = asm_mul_reg(2, 2, 3);
    emit_word(word);
}

int* jit_script(char *input) {
    binary_pos = 0;

    struct Substr remain={input, strlen(input)};
    int val;

    while(!is_end(&remain)) {
        skip_space(&remain);
        if(is_number(remain.ptr)) {
            val = parse_number(remain.ptr);
            emit_push_val(val);
            skip_token(&remain);
            continue;
        }else if(is_register(remain.ptr)) {
            if(remain.ptr[1] == '1') {
                emit_push_reg(1);
            } else {
                emit_push_reg(0);
            }
            skip_token(&remain);
            continue;
        } else {
            // must be op.

            val = parse_word(&remain);
            skip_token(&remain);

            emit_pop_r2_r3();

            switch(val) {
                case OP_ADD:
                    emit_add_r2_r3();
                    break;
                case OP_SUB:
                    emit_sub_r2_r3();
                    break;
                case OP_MUL:
                    emit_mul_r2_r3();
                    break;
                case OP_DIV:
                    fprintf(stderr, "div not supported\n");
                    exit(1);
                    break;
            }
            // result is in r2.
            emit_push_reg(2);
            continue;
        }
    }
    // final result, pop to r0
    emit_pop_reg(0);
    emit_mov_reg(15, 14);

    return binary_buf;
}

static void run_unit_tests() {
    printf("all test done\n");
}


int main() {
    int res;
    int (*funcvar)(int, int);

    run_unit_tests();

    res = eval(1, 5, "3 7 add r1 sub 4 mul");
    printf("res=%d\n", res);

    /*
     TODO: Make below test pass.
    */
    init_jit();

    funcvar = (int(*)(int,int))jit_script("3 7 add r1 sub 4 mul");
    // funcvar = (int(*)(int,int))jit_script("3 7 add 5 sub 4 mul");
    // funcvar = (int(*)(int,int))jit_script("3 7 add");
    /*
        // mov r0, #5
    binary_buf[0] = 0xe3a00005;
    // mov r15, r14
    binary_buf[1] = 0xe1a0f00e;
    */


   /* OK
   binary_pos = 0;
    int word = asm_mov_imm(2, 3);
    printf("%x\n", word);
    emit_word(word);
    word = asm_stmdb(13, 1<<2);
    printf("%x\n", word);
    emit_word(word);
    word = asm_mov_imm(2, 7);
    printf("%x\n", word);
    emit_word(word);
    word = asm_stmdb(13, 1<<2);
    printf("%x\n", word);
    emit_word(word);

    // 1100 = c
    word = asm_ldmia(13, 0x0c);
    printf("%x\n", word);
    emit_word(word);

    word = asm_add_reg(2, 2, 3);
    printf("%x\n", word);
    emit_word(word);

    word = asm_stmdb(13, 1<<2);
    printf("%x\n", word);
    emit_word(word);

    word = asm_ldmia(13, 0x01);
    printf("%x\n", word);
    emit_word(word);
    word = asm_mov_reg(15, 14);
    printf("%x\n", word);
    emit_word(word);
    funcvar = (int(*)(int,int))binary_buf;
    */
 
    /* OK
    binary_pos = 0;
    int word = asm_mov_imm(2, 8);
    printf("%x\n", word);
    emit_word(word);

//    word = asm_strdb(2, 13);
    word = asm_stmdb(13, 0x04);
    printf("%x\n", word);
    emit_word(word);
    word = asm_ldmia(13, 0x01);
    printf("%x\n", word);
    emit_word(word);
    word = asm_mov_reg(15, 14);
    printf("%x\n", word);
    emit_word(word);
    funcvar = (int(*)(int,int))binary_buf;
    */

    /*
    asm_ldria(0, 13);
    printf("%x\n", word);
    emit_word(word);
    */

    /*OK
    int word = asm_mov_imm(2, 3);
    printf("%x\n", word);
    emit_word(word);
    word = asm_mov_imm(3, 7);
    printf("%x\n", word);
    emit_word(word);
    word = asm_add_reg(2, 0, 3);
    printf("%x\n", word);
    emit_word(word);
    word = asm_mov_reg(15, 14);
    printf("%x\n", word);
    emit_word(word);
    funcvar = (int(*)(int,int))binary_buf;

    */

    /* OK.
    int word = asm_mov_imm(0, 5);
    printf("%x\n", word);
    emit_word(word);
    word = asm_mov_reg(15, 14);
    printf("%x\n", word);
    emit_word(word);
    funcvar = (int(*)(int,int))binary_buf;
    */


    res = funcvar(1, 5);
    printf("res jit =%d\n", res);
    assert_int_eq(20, res);

    res = funcvar(1, 4);
    assert_int_eq(24, res);

    return 0;
}