linux - 在汇编中从/dev/random 返回一个字节

Question

我正在尝试打开 /dev/random，从中读取一个字节并以状态退出...在 x86 程序集中。这似乎会返回随机数，但我不确定它是否如我所想。

# Where do we get our random numbers from
.data
    random: .ascii "/dev/random\0"

# Program goes here
.text
    .global _start
    _start:

    # Get /dev/random fd
    movl $5, %eax      # sys_open (originally $0 by accident)
    movl $random, %ebx # Filename string
    movl $0, %ecx      # O_RDONLY flag
    int $0x80

    # Read one byte onto stack
    movl %eax, %ebx    # The result of sys_open
    movl $3, %eax      # sys_read
    subl $1, %esp      # Make stack space
    movl %esp, %ecx    # Make stack our buffer
    movl $1, %edx      # size_t bytes? only 1
    int $0x80

    # Exit with a random result
    movl %esp, %ebx    # random result as exit status
    movl $1, %eax      # sys_exit
    int $0x80

当我通过 strace 运行它时，我得到以下结果:

execve("./random", ["./random"], [/* 44 vars */]) = 0
fstat(0, NULL)                          = 3
close(0)                                = -1 EFAULT (Bad address)
write(0, NULL, 1 <unfinished ...>
+++ exited with 12 +++

注意缺少 open() 和 read()!另外，exit() 去了哪里？

我做错了什么？

Answer 1

要进行系统调用，您必须遵循内核的系统调用API。因为我不知道它是什么，所以我总是look it up online .然后我发现 sys_open 应该是这样的:

mov $5, %eax          ;; syscall number "open"
mov $random, %ebx     ;; arg 1: char * filename
mov $0, %ecx          ;; arg 2: int flags
int $0x80