stack-exec.c

#include "kernel/types.h"
#include "kernel/memlayout.h"
#include "user/user.h"

/*
  # test.S
  # riscv64-unknown-elf-as -march=rv64gc -fpic test.S
  # riscv64-unknown-elf-objdump -d /tmp/a.out

  # write(1, s, sizeof(s))

  # fd = 1
  li a0, 1
  # syscall write -> a7 = 16
  li a7, 16

  # looking for the address of the string to print, after ret (0x82, 0x80)

  auipc a1, 0
  .loop:
  lbu t0, 0(a1)
  addi a1, a1, 1
  li t1, 0x80
  beq t0, t1, .endloop
  j .loop
  .endloop:

  # computing the length of the string, look for 0 byte
  mv a2, a1
  .loop2:
  lbu t0, 0(a2)
  addi a2, a2, 1
  beq t0, zero, .endloop2
  j .loop2
  .endloop2:
  sub a2, a2, a1

  ecall

  ret

  .mystring:
  auipc a1, 4
  ret
  "Hello"
  .mystringend:
  auipc a2, -4
  ret

*/


char code[] = {
  // li a0, 1
  0x05, 0x45,
  // li a7, 16
  0xc1, 0x48,
  // auipc a1, 0
  0x97, 0x05, 0x00, 0x00,
  // .loop:
  // lbu t0, 0(a1)
  0x83, 0xc2, 0x05, 0x00,
  // addi a1, a1, 1
  0x85, 0x05,
  //li t1, 0x80
  0x13, 0x03, 0x00, 0x08,
  // beq t0 t1, .endloop
  0x63, 0x83, 0x62, 0x00,
  // j .loop
  0xcd, 0xbf,
  // .endloop:
  // mv a2, a1
  0x2e, 0x86,
  // .loop2:
  // lbu t0, 0(a2)
  0x83, 0x42, 0x06, 0x00,
  // addi a2, a2, 1
  0x05, 0x06,
  // beqz t0, .endloop2
  0x63, 0x83, 0x02, 0x00,
  // j .loop2
  0xdd, 0xbf,
  // .endloop2
  // sub a2, a2, a1
  0x0d, 0x8e,
  // ecall
  0x73, 0x00, 0x00, 0x00,
  // ret
  0x82, 0x80,
  'H', 'e', 'l', 'l', 'o', '!', 0x0a, 0
};

void do_fork(void (*fn)(void)){
  int pid = fork();
  if(pid < 0){
    printf("fork failed\n"); exit(1);
  } else if (pid == 0){
    fn();
  } else {
    wait(0);
  }
}

void test_code1(){
  ((void(*)(void))(code))();
  printf("code1: cette ligne devrait-elle s'afficher ?\n");
  exit(0);
}

void test_code2(){
  char code2[100];
  for(int i = 0; i < sizeof(code); i++){
    code2[i] = code[i];
  }

  ((void(*)(void))(code2))();
  printf("code2: cette ligne devrait-elle s'afficher ?\n");
  exit(0);
}

int
main(int argc, char *argv[])
{
  do_fork(test_code1);
  do_fork(test_code2);
  exit(0);
}