Re: How to map machine instctions in memory and execute them? (Aka, how to create a loader)

[rempas via Digitalmars-d-learn]

On Monday, 6 June 2022 at 15:13:45 UTC, rempas wrote:
In case someone is wondering, I found an answer in another
forum. The code is the following:

```d
import core.stdc.stdio;
import core.stdc.string;
import core.stdc.stdlib;
import core.sys.posix.sys.mman;

void putbytes(char **code, const char *bytes) {
  uint bt;
  for (int i = 0, n; sscanf(bytes + i, "%x%n", &bt, &n) == 1; i 
+= n)
    { *(*code)++ = cast(char)bt; }
}

void putdata(char **code, char** data) {
  memcpy(*code, data, (*data).sizeof);
  *code += (*data).sizeof;
}

extern (C) void main() {
  char *data = cast(char*)mmap(null, cast(ulong)15, PROT_READ | 
PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
  strcpy(data, "Hello world!\n");

  char *code = cast(char*)mmap(null, cast(ulong)500, PROT_READ | 
PROT_WRITE | PROT_EXEC, MAP_PRIVATE | MAP_ANON, -1, 0);
  char *pos = code;

  // Call the "write" and "exit" system calls
  putbytes(&pos, "48 C7 C0 1 0 0 0");    // mov rax, 0x01     
(write syscall)
  putbytes(&pos, "48 C7 C7 1 0 0 0");    // mov rdi, 0x01     
(stdout)
  putbytes(&pos, "48 C7 C2 D 0 0 0");   // mov rdx, 13       
(string length)
  putbytes(&pos, "48 BE");                      // movabs rsi, 
data  (string address)
  putdata(&pos, &data);
  putbytes(&pos, "0F 05");                        // syscall
  putbytes(&pos, "48 C7 C0 3C 0 0 0");  // mov rax, 0x3C     
(exit syscall)
  putbytes(&pos, "0F 05");                       // syscall

  // Execute the code
  (cast(void* function())code)();
}
```