如何动态生成和运行本机代码？ [英] How to generate and run native code dynamically?

问题描述

我想为我写的一个玩具语言处理器（纯粹学术）编写一个非常小的概念验证JIT编译器，但是我在设计的中间高度有一些麻烦。从概念上讲，我熟悉JIT如何工作 - 你编译字节码（机器或程序集）代码运行。然而，在螺母和螺栓的水平，我不是真的抓住你如何 。

I'd like to write a very small proof-of-concept JIT compiler for a toy language processor I've written (purely academic), but I'm having some trouble in the middle-altitudes of design. Conceptually, I'm familiar with how JIT works - you compile bytecode into (machine or assembly?) code to run. At the nuts-and-bolts level however, I'm not quite gripping how you actually go about doing that.

我的（非常newb）膝盖反应，因为我没有第一个线索从哪里开始，将尝试类似如下：

My (very "newb") knee-jerk reaction, since I haven't the first clue where to start, would be to try something like the following:

1. mmap（）一个内存块，设置对PROT_EXEC的访问


2. 将本地代码写入块




4. 修改当前寄存器以指向映射区域中的本地代码块

1. mmap() a block of memory, setting access to PROT_EXEC
2. write the native code into the block
3. store the current registers (stack pointer, et al.) someplace cozy
4. modify the current registers to point into the native code block in the mapped region
5. the native code would now get executed by the machine
6. restore the previous registers

就是这个甚至关闭到一个/正确的算法？我试过仔细阅读我知道有JIT编译器学习的不同项目（如 V8 ），但这些代码库

Is that even close to a/the correct algorithm? I've tried perusing different projects that I know have JIT compilers to study (such as V8) but these codebases turn out to be difficult to consume because of their size, and I've little idea where to start looking.

推荐答案

不知道linux是什么，但它适用于x86 / windows。

更新： http://codepad.org/sQoF6kR8

Not sure about linux, but this works on x86/windows.
Update: http://codepad.org/sQoF6kR8

#include <stdio.h>
#include <windows.h>

typedef unsigned char byte;

int arg1;
int arg2;
int res1;

typedef void (*pfunc)(void);

union funcptr {
  pfunc x;
  byte* y;
};

int main( void ) {

  byte* buf = (byte*)VirtualAllocEx( GetCurrentProcess(), 0, 1<<16, MEM_COMMIT, PAGE_EXECUTE_READWRITE );

  if( buf==0 ) return 0;

  byte* p = buf;

  *p++ = 0x50; // push eax
  *p++ = 0x52; // push edx

  *p++ = 0xA1; // mov eax, [arg2]
  (int*&)p[0] = &arg2; p+=sizeof(int*);

  *p++ = 0x92; // xchg edx,eax

  *p++ = 0xA1; // mov eax, [arg1]
  (int*&)p[0] = &arg1; p+=sizeof(int*);

  *p++ = 0xF7; *p++ = 0xEA; // imul edx

  *p++ = 0xA3; // mov [res1],eax
  (int*&)p[0] = &res1; p+=sizeof(int*);

  *p++ = 0x5A; // pop edx
  *p++ = 0x58; // pop eax
  *p++ = 0xC3; // ret

  funcptr func;
  func.y = buf;

  arg1 = 123; arg2 = 321; res1 = 0;

  func.x(); // call generated code

  printf( "arg1=%i arg2=%i arg1*arg2=%i func(arg1,arg2)=%i\n", arg1,arg2,arg1*arg2,res1 );

}

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