Question

我想从asm调用lseek和llseek系统调用（不使用glibc包装器，我这样做是为了学习目的）。我写下面的代码来做到这一点，但是当我运行它时，它显示了我理解正在发生的分段错误，因为我试图从分配给我们的块中访问内存。我能以任何方式解决它吗？

section .text
   global _start         ;must be declared for using gcc

_start:  

   ;open the file for reading
   mov eax, 5
   mov ebx, file_name
   mov ecx, 2             ;for RDWD access
   mov edx, 0777          ;read, write and execute by all
   int  0x80

   mov  [fd_out], eax

   ; write into the file
   mov  edx,len          ;number of bytes
   mov  ecx, msg         ;message to write
   mov  ebx, [fd_out]    ;file descriptor 
   mov  eax,4            ;system call number (sys_write)
   int  0x80             ;call kernel

   ;change offset
   mov eax, 19
   mov ebx, [fd_out]
   mov ecx, 7             ;for read only access
   mov edx, 0             ;SEEK_SET
   int  0x80

   ; write into the file
   mov  edx,lntwo          ;number of bytes
   mov  ecx, mgafter         ;message to write
   mov  ebx, [fd_out]    ;file descriptor 
   mov  eax,4            ;system call number (sys_write)
   int  0x80             ;call kernel


section .data
file_name db 'myfile.txt'
msg db 'Welcome to jj'
mgafter db ' Shashwat'
lntwo equ $-mgafter
len equ  $-msg

section .bss
fd_out resb 1
fd_in  resb 1
info resb  26

如何从程序集调用lseek和_llseek系统调用

0 个答案: