gistfile1.txt

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

typedef int(*fn)(void*, void*);
typedef int(*lel)(void*);

int say_hello(void* f) {
    int* val = (int*)f;
    printf("Say hello: %d\n", *val);
    sleep(10);
    return 12;
}

fn compile_blech(void) {
  char *memory = mmap(NULL,             // address
                      4096,             // size
                      PROT_READ | PROT_WRITE | PROT_EXEC,
                      MAP_PRIVATE | MAP_ANONYMOUS,
                      -1,               // fd (not used here)
                      0);               // offset (not used here)
  if (!memory) {
    perror("failed to allocate memory");
    exit(1);
  }

   //0x000000000000120e <+0>:     f3 0f 1e fa     endbr64
   //0x0000000000001212 <+4>:     48 83 ec 08     sub    $0x8,%rsp
   //0x0000000000001216 <+8>:     48 89 f8        mov    %rdi,%rax
   //0x0000000000001219 <+11>:    48 89 f7        mov    %rsi,%rdi
   //0x000000000000121c <+14>:    ff d0   callq  *%rax
   //0x000000000000121e <+16>:    48 83 c4 08     add    $0x8,%rsp
   //0x0000000000001222 <+20>:    c3      retq

   //0x000000000000120e <+0>:     f3 0f 1e fa     endbr64
   //0x0000000000001212 <+4>:     48 83 ec 08     sub    $0x8,%rsp
   //0x0000000000001216 <+8>:     48 89 f8        mov    %rdi,%rax
   //0x0000000000001219 <+11>:    48 89 f7        mov    %rsi,%rdi
   //0x000000000000121c <+14>:    ff d0   callq  *%rax
   //0x000000000000121e <+16>:    48 83 c4 08     add    $0x8,%rsp
   //0x0000000000001222 <+20>:    c3      retq

  int i = 0;
  memory[i++] = 0xf3;
  memory[i++] = 0x0f;
  memory[i++] = 0x1e;
  memory[i++] = 0xfa;
  memory[i++] = 0x48;
  memory[i++] = 0x83;
  memory[i++] = 0xec;
  memory[i++] = 0x08;
  memory[i++] = 0x48;
  memory[i++] = 0x89;
  memory[i++] = 0xf8;
  memory[i++] = 0x48;
  memory[i++] = 0x89;
  memory[i++] = 0xf7;
  memory[i++] = 0xff;
  memory[i++] = 0xd0;
  memory[i++] = 0x48;
  memory[i++] = 0x83;
  memory[i++] = 0xc4;
  memory[i++] = 0x08;
  memory[i++] = 0xc3;

  return (fn) memory;
}

int do_the_thing() {
  fn f = compile_blech();
  int i = 42;
  int ret = f(&say_hello, &i);
  printf("Say goodby: %d\n", ret);
  munmap(f, 4096);
  return 0;
}

int main () {
    do_the_thing();
}