如何在汇编Linux x86中使用chmod（）？

Question

How can i use chmod() to change file permissions in Assembly linux x86 ? i want a sample code in assembly , i see help guide but still it's very hard to understand

http://man7.org/linux/man-pages/man2/chmod.2.html

int chmod(const char *pathname, mode_t mode);

chmod() have 2 argv , first is pathfile name and second is mod !

path /Users/paul/Desktop/file.txt and mode_t modes are : S_ISUID , S_ISGID , S_ISVTX , S_IRUSR ,S_IWUSR

and more can see in url first question: i need set these values in the varible of ecx or i must use values numbers ,which one i must use ? S_IWGRP or 00020 #write by group

second question: Am i doing it truely ? i put these in ecx and execute same this :

mov eax,15   
mov ebx,mypathfile
mov ecx,S_IWUSR
int 0x80

someone can get me code example ?

and the last question is , how can i set 777 permission to file (read write execute for all) ?

Thanks.

Answer 1

Here is the full program. That should answer your questions.

main.asm:

        global _start
        section .text

_start:
        mov eax, 15             ; sys_chmod                                     
        mov ebx, path
        mov ecx, 0777o
        int 0x80

        mov eax, 1              ; sys_exit                                      
        mov ebx, 0
        int 0x80

        section .data

path:   db "file.ext", 0

Build with:

nasm -f elf32 -o main.o main.asm
ld -m elf_i386 -o main main.o