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trying to emulate linux command in x86_64 assembly

I really need your help. so i am basicly trying to emulate Linux rm* command using assembly language :

when i ran strace on the command this is what i've got:

Code:

execve("/bin/rm", ["rm", "test1", "test2"], 0x7ffc85aaee50 /* 56 vars */) = 0

brk(NULL) = 0x556102fd1000

access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=98111, ...}) = 0

mmap(NULL, 98111, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7ffbf7d17000

close(3) = 0

access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)

openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3

read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\34\2\0\0\0\0\0"..., 832) = 832

fstat(3, {st_mode=S_IFREG|0755, st_size=2030544, ...}) = 0

mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7ffbf7d15000

mmap(NULL, 4131552, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7ffbf7717000

mprotect(0x7ffbf78fe000, 2097152, PROT_NONE) = 0

mmap(0x7ffbf7afe000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1e7000) = 0x7ffbf7afe000

mmap(0x7ffbf7b04000, 15072, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7ffbf7b04000

close(3) = 0

arch_prctl(ARCH_SET_FS, 0x7ffbf7d16540) = 0

mprotect(0x7ffbf7afe000, 16384, PROT_READ) = 0

mprotect(0x556102aee000, 4096, PROT_READ) = 0

mprotect(0x7ffbf7d2f000, 4096, PROT_READ) = 0

munmap(0x7ffbf7d17000, 98111) = 0

brk(NULL) = 0x556102fd1000

brk(0x556102ff2000) = 0x556102ff2000

openat(AT_FDCWD, "/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=4584960, ...}) = 0

mmap(NULL, 4584960, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7ffbf72b7000

close(3) = 0

ioctl(0, TCGETS, {B38400 opost isig icanon echo ...}) = 0

newfstatat(AT_FDCWD, "test1", {st_mode=S_IFREG|0664, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0

geteuid() = 1000

newfstatat(AT_FDCWD, "test1", {st_mode=S_IFREG|0664, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0

faccessat(AT_FDCWD, "test1", W_OK) = 0

unlinkat(AT_FDCWD, "test1", 0) = 0

newfstatat(AT_FDCWD, "test2", {st_mode=S_IFREG|0664, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0

newfstatat(AT_FDCWD, "test2", {st_mode=S_IFREG|0664, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0

faccessat(AT_FDCWD, "test2", W_OK) = 0

unlinkat(AT_FDCWD, "test2", 0) = 0

lseek(0, 0, SEEK_CUR) = -1 ESPIPE (Illegal seek)

close(0) = 0

close(1) = 0

close(2) = 0

exit_group(0) = ?

+++ exited with 0 +++

here is the code i previously wrote

Code:

global _start



section .text



_start:







mov rax,        87        ;sys_unlink

mov rdi, fname

syscall





exit:

mov rax,        60

mov rdi,        80

syscall



section .data



fname : db "test.txt",0

but as you can see i have to declare file name . and i don't wanna do that. now my assumption is to do something with getdents64 sys_call and list files in some buffer and then unlink them. but i don't actually know how to do that. any help would be appreciated. thank you

Welcome to LQ!

Please place your code snippets inside [CODE]...[/CODE] tags for better readability. You may type those yourself or click the "#" button in the edit controls.

The asterisk in rm * is interpreted by the shell. The shell performs a directory lookup, and you are right: It's probably getdents. You will have to open the current directory and use the file descriptor thus obtained to make the call to getdents. Then loop over the getdents results and unlink the names.

The getdents man page (see link above) contains a sample C program. I will leave it up to you to turn that into assembly code.

pointer to a filename in linux x86_64 assembly

So i am trying to make a program that loops through directory, and deletes every file in it, so i am using getdents64 system call to do this. and since getdents returns number of bytes read from directory. i cannot loop through it. so i obviously need to point to the filename in a directory. but i really don't know how to do it,

this code will not work, when you run strace on it you will get this output, obiously i have put the output of a program running without a loop, you can guess what happens when i run it in a loop

strace output:

Code:

execve("./whiper", ["./whiper"], 0x7ffe7ac97400 /* 58 vars */) = 0

open("test", O_RDONLY)                  = 3

getdents64(3, /* 7 entries */, 2040)    = 224

close(3)                                = 0

unlink(0xe0)                            = -1 EFAULT (Bad address)

exit(80)                                = ?

+++ exited with 80 +++

and here is my code:

Code:

global _start



section .data



        dir : db "test",0

        len: equ 2040                ;define buffer size



section .bss

        buffer:  resb len        





section .text



_start:



        

        ;open folder

        mov rax,        2        ;sys_open

        mov rdi,        dir        ;folder to open

        mov rsi,        0        ;read only

        mov rdx,        0        

        syscall        



        cmp rax,        0      ;if there is no folder go to exit

        jbe exit

list:

        mov rdi,        rax        ;directory in rdi

        mov rax,        217        ;sys_getdents64

        mov rsi,        buffer        

        mov rdx,        len    ;length of the 

        syscall

        

        xchg r10,        rax        ;save buffer in r10 to loop through it

        xor rax,        rax        ;zero out rax for the next system call

close:

        mov rax,        3        ;sys_close

        syscall

unlink:

        cmp r10,        0        ;if done, exit the program

        jbe exit    

        mov rax,        87        ;sys_unlink

        mov rdi,        r10          ;list of files 

        syscall

        jmp unlink        



exit:

        mov rax,        60        ;sys_exit

        mov rdi,        80

        syscall

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