如何从代码编译代码

Question

我想试验用 C 代码编写程序的程序，我想使用如下构造：

int main() {
    char* srcCode="int f(int x) { return x+42; }";
    int (*compiledFun)(int) = compile(srcCode);
    printf("result=%d", (*compiledFun)(123));
    return 0;
}

所需的输出应打印为“result=165”。

我的问题是关于compile() 函数。我可能会尝试将srcCode 放在一个文件中，然后调用外部编译器，例如gcc，然后尝试读取生成的二进制文件，可能修复一些地址，以便填充compiledFun 内存。但我觉得那将是一个非常低效的存根。有没有办法从程序内部直接从内存编译程序？可能是某个库或可以从 gcc 源中窃取的子集，负责从源文本生成二进制代码？

---

这可能是重要的补充，所有应该编译的源代码都是一个接受参数并返回的函数。它不会像printf那样调用任何外部库和函数，而只是做一些计算并返回。

Answer 1

使用来自 TinyC 的 libtcc 内存中 C 编译器。

这里有一个完整的例子https://github.com/TinyCC/tinycc/blob/mob/tests/libtcc_test.c

/*
 * Simple Test program for libtcc
 *
 * libtcc can be useful to use tcc as a "backend" for a code generator.
 */
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include "libtcc.h"

/* this function is called by the generated code */
int add(int a, int b)
{
    return a + b;
}

/* this strinc is referenced by the generated code */
const char hello[] = "Hello World!";

char my_program[] =
"#include <tcclib.h>\n" /* include the "Simple libc header for TCC" */
"extern int add(int a, int b);\n"
"#ifdef _WIN32\n" /* dynamically linked data needs 'dllimport' */
" __attribute__((dllimport))\n"
"#endif\n"
"extern const char hello[];\n"
"int fib(int n)\n"
"{\n"
"    if (n <= 2)\n"
"        return 1;\n"
"    else\n"
"        return fib(n-1) + fib(n-2);\n"
"}\n"
"\n"
"int foo(int n)\n"
"{\n"
"    printf(\"%s\\n\", hello);\n"
"    printf(\"fib(%d) = %d\\n\", n, fib(n));\n"
"    printf(\"add(%d, %d) = %d\\n\", n, 2 * n, add(n, 2 * n));\n"
"    return 0;\n"
"}\n";

int main(int argc, char **argv)
{
    TCCState *s;
    int i;
    int (*func)(int);

    s = tcc_new();
    if (!s) {
        fprintf(stderr, "Could not create tcc state\n");
        exit(1);
    }

    /* if tcclib.h and libtcc1.a are not installed, where can we find them */
    for (i = 1; i < argc; ++i) {
        char *a = argv[i];
        if (a[0] == '-') {
            if (a[1] == 'B')
                tcc_set_lib_path(s, a+2);
            else if (a[1] == 'I')
                tcc_add_include_path(s, a+2);
            else if (a[1] == 'L')
                tcc_add_library_path(s, a+2);
        }
    }

    /* MUST BE CALLED before any compilation */
    tcc_set_output_type(s, TCC_OUTPUT_MEMORY);

    if (tcc_compile_string(s, my_program) == -1)
        return 1;

    /* as a test, we add symbols that the compiled program can use.
       You may also open a dll with tcc_add_dll() and use symbols from that */
    tcc_add_symbol(s, "add", add);
    tcc_add_symbol(s, "hello", hello);

    /* relocate the code */
    if (tcc_relocate(s, TCC_RELOCATE_AUTO) < 0)
        return 1;

    /* get entry symbol */
    func = tcc_get_symbol(s, "foo");
    if (!func)
        return 1;

    /* run the code */
    func(32);

    /* delete the state */
    tcc_delete(s);

    return 0;
}