How to include a text file?

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ntos

Joined: 06 Jul 2023
Posts: 18

ntos 27 Jul 2023, 08:42

Hi,
I have a text file in the same folder as the source code and define the file like this:

Code:

format ELF64

section '.text' executable
public main
main:
        mov rax, 2 ; open system call
    mov rdi, filename ; pointer to file name
    mov rsi, flags ; flags for opening
    mov rdx, 0 ; mode (ignored)
    syscall ; invoke system call

; check if rax is negative (error)
cmp rax, 0
jl error

; rax contains a valid file descriptor
mov rdi, 1 ; file descriptor for stdout
mov rsi, rax ; file descriptor for test.txt
mov rdx, 0 ; offset (ignored)
mov r10, 0 ; count (0 means until EOF)
mov rax, 40 ; sendfile system call
syscall ; invoke system call

; close the file
mov rdi, rsi ; file descriptor for test.txt
mov rax, 3 ; close system call
syscall

mov rdi, 0 ; exit status
mov rax, 60 ; exit system call
syscall
error:

mov rdi, 1 ; exit status
mov rax, 60 ; exit system call
syscall

section '.data'
    filename file 'test.txt' ; null-terminated string
    flags    =  0 ; O_RDONLY

This code is run in SASM IDE but it throws this error:

processed: filename file 'test.txt'
error: file not found.

strace throws the same error, too.

Thanks for reading.

27 Jul 2023, 08:42

bitshifter

Joined: 04 Dec 2007
Posts: 796
Location: Massachusetts, USA

bitshifter 27 Jul 2023, 10:33

'file' is reserved keyword in fasm to place object inline with no preprocessing or assembling.

i cant test this code but this part is obvious

Code:

filename file 'test.txt' ; null-terminated string

try

Code:

filename db 'test.txt',0 ; null-terminated string

_________________
Coding a 3D game engine with fasm is like trying to eat an elephant,
you just have to keep focused and take it one 'byte' at a time.

27 Jul 2023, 10:33

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 27 Jul 2023, 13:49

If you want to include the file as part of the output binary.

Code:

section '.data'
    file 'test.txt'

27 Jul 2023, 13:49

ntos

Joined: 06 Jul 2023
Posts: 18

ntos 27 Jul 2023, 21:56

@bitshifter. It worked. Thanks.
@revolution. So the file directive is to include some file as part of the output binary, nothing more nothing less, right? Like some license or readme file?

27 Jul 2023, 21:56

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 27 Jul 2023, 22:03

ntos wrote:

@revolution. So the file directive is to include some file as part of the output binary, nothing more nothing less, right? Like some license or readme file?

It could be anything. A binary fine, whatever. It just makes a duplicate without any parsing of the contents.

27 Jul 2023, 22:03

ntos

Joined: 06 Jul 2023
Posts: 18

ntos 28 Jul 2023, 13:39

revolution wrote:

ntos wrote:
@revolution. So the file directive is to include some file as part of the output binary, nothing more nothing less, right? Like some license or readme file?
It could be anything. A binary fine, whatever. It just makes a duplicate without any parsing of the contents.

Then how do you access the file defined with File from fasm code?

28 Jul 2023, 13:39

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 28 Jul 2023, 14:05

Put a label.

Code:

my_data: file 'test.txt'
;...
lea rax,[my_data]
mov bl,[rax]

28 Jul 2023, 14:05

ntos

Joined: 06 Jul 2023
Posts: 18

ntos 28 Jul 2023, 22:10

revolution wrote:

Put a label.

Code:

my_data: file 'test.txt'
;...
lea rax,[my_data]
mov bl,[rax]

Thank you very much.

28 Jul 2023, 22:10

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