Katyusha's blog

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#include <stdio.h>
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#include <stdbool.h>
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#include <dlfcn.h>
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#include <unistd.h>
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#include <sys/wait.h>
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#include <string.h>
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#include <stdlib.h>
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#include <readline/readline.h>
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#include <readline/history.h>
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const char C_PATH[] = "/tmp/tmp.c";
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char SO_PATH[1 << 16], _buffer[1 << 16];
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extern char ** environ;
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char *fun_sig[105];
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int fun_cnt = 0;
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// Compile a function definition and load it
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bool compile_and_load_function(const char* function_def) {
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    FILE *fp = fopen(C_PATH, "w");
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    for (int i = 0; i < fun_cnt; i++) {
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        fprintf(fp, "%s\n", fun_sig[i]);
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    }
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    fprintf(fp, "%s\n", function_def);
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    fclose(fp);
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    sprintf(SO_PATH, "/tmp/tmp%d.so", fun_cnt);
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    int pid = fork();
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    if (pid == 0) {
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        const char *argv[] = {
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            "gcc", "-shared", "-fPIC", C_PATH, "-o", SO_PATH, NULL
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        };
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        execve("/usr/bin/gcc", argv, environ);
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        _exit(1);
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    } else {
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        int status;
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        void *handle;
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        if (waitpid(pid, &status, 0) < 0) return 0;
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        if (!(WIFEXITED(status) && WEXITSTATUS(status) == 0)) return 0;
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        if ((handle = dlopen(SO_PATH, RTLD_NOW | RTLD_GLOBAL)) == NULL) return 0;
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        int n = strlen(function_def);
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        int ptr = 0;
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        for (int i = 0; i < n; i++) {
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            if (function_def[i] == '{') break;
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            _buffer[ptr++] = function_def[i];
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        }
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        _buffer[ptr++] = ';';
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        _buffer[ptr] = '\0';
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        fun_sig[fun_cnt++] = (char *)malloc(sizeof(char) * (ptr + 1));
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        memcpy(fun_sig[fun_cnt - 1], _buffer, ptr + 1);
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    }
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    return 1;
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}
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// Evaluate an expression
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int expr_cnt = 0;
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bool evaluate_expression(const char* expression, int* result) {
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    int len = 0;
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    for (int i = 0 ; i < fun_cnt; i++) {
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        sprintf(_buffer + len, "%s\n", fun_sig[i]);
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        len += strlen(fun_sig[i]) + 1;
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    }
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    sprintf(_buffer + len, "int expr(){return %s;}", expression);
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    FILE *fp = fopen(C_PATH, "w");
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    fprintf(fp, "%s", _buffer);
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    fclose(fp);
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    sprintf(SO_PATH, "/tmp/expr%d.so", expr_cnt);
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    int pid = fork();
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    if (pid == 0) {
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        const char *argv[] = {
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            "gcc", "-shared", "-fPIC", C_PATH, "-o", SO_PATH, NULL
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        };
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        execve("/usr/bin/gcc", argv, environ);
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        _exit(1);
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    } else {
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        int status;
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        void *handle;
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        int (*fun)();
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        if (waitpid(pid, &status, 0) < 0) return 0;
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        if (!(WIFEXITED(status) && WEXITSTATUS(status) == 0)) return 0;
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        if ((handle = dlopen(SO_PATH, RTLD_NOW | RTLD_GLOBAL)) == NULL) return 0;
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        if ((fun = dlsym(handle, "expr")) == NULL) return 0;
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        ++expr_cnt;
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        *result = fun();
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    }
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    return 1;
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}
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bool is_function(const char *buf) {
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    if (strlen(buf) >= 3 && buf[0] == 'i' && buf[1] == 'n' && buf[2] == 't') return 1;
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    return 0;
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}
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int main() {
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    while (1) {
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        char *buffer = readline("crepl>");
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        if (buffer == NULL) break;
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        add_history(buffer);
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        int ptr = 0;
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        while (ptr < (1 << 16) && buffer[ptr] == ' ') ptr++;
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        char *_buffer = buffer + ptr;
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        if (is_function(_buffer)) {
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            if (compile_and_load_function(_buffer)) {
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                printf("Ok, function added.\n");
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            } else {
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                printf("Function input error!\n");
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            }
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        }
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        else {
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            int res;
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            if (evaluate_expression(_buffer, &res)) {
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                printf("Expression evaluated = %d.\n", res);
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            } else {
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                printf("Expression input error!\n");
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            }
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        }
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    }
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}