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I am writing assembly code for my university course and it is not working at all. I have never written code like this before and I'm unsure what I am doing wrong. The code links to a few other codes for different things. Here is the code:
%include "asm_io.inc"
section .data
name_prompt db "Enter your name: ", 0
count_prompt db "Enter the number of repetitions (50-100): ", 0
error_msg db "Error: Number must be between 50 and 100.", 10, 0
welcome_msg db "Welcome, ", 0
newline db 10, 0
section .bss
name resb 128 ; Allocate 128 bytes for the name
num_reps resd 1
section .text
global asm_main ; Declare the function to be used by the C code
extern print_string ; External declarations from asm_io.inc
extern read_char
extern read_int
extern print_nl
asm_main: ; Entry point for the C code
push ebp ; Save the base pointer (set up stack frame)
mov ebp, esp ; Move stack pointer into base pointer
; Prompt for name
push name_prompt
call print_string
add esp, 4 ; Properly clean up the stack after calling print_string
; Read the name character-by-character
lea eax, [name]
call read_char_loop
call print_nl
validate_reps:
; Prompt for number of repetitions
push count_prompt
call print_string
add esp, 4
; Read number of repetitions
call read_int
mov [num_reps], eax
; Validate repetitions (must be between 50 and 100)
cmp eax, 50
jl invalid_reps
cmp eax, 100
jg invalid_reps
; Print welcome message the number of times specified
mov ecx, [num_reps]
print_loop:
cmp ecx, 0
jle end_loop
push welcome_msg
call print_string
add esp, 4
lea eax, [name]
push eax
call print_string
add esp, 4
call print_nl
dec ecx
jmp print_loop
invalid_reps:
push error_msg
call print_string
add esp, 4
call print_nl
jmp validate_reps
end_loop:
; Exit program cleanly using the exit system call
mov eax, 1 ; SYS_exit
xor ebx, ebx ; Status code 0
int 0x80
read_char_loop:
lea edi, [name]
mov ecx, 128
read_next_char:
call read_char
cmp al, 10
je end_read_char
mov [edi], al
inc edi
loop read_next_char
end_read_char:
mov byte [edi], 0
ret
After running a debugger I believe the segmentation fault is happening within the print_string function which is related to the manipulation of the stack and memory access.
Also "asm_io.inc" is this code below:
extern read_int, print_int, print_string
extern read_char, print_char, print_nl
extern sub_dump_regs, sub_dump_mem, sub_dump_math, sub_dump_stack
%macro dump_regs 1
push dword %1
call sub_dump_regs
%endmacro
;
; usage: dump_mem label, start-address, # paragraphs
%macro dump_mem 3
push dword %1
push dword %2
push dword %3
call sub_dump_mem
%endmacro
%macro dump_math 1
push dword %1
call sub_dump_math
%endmacro
%macro dump_stack 3
push dword %3
push dword %2
push dword %1
call sub_dump_stack
%endmacro
I was given that code and also a code called asm_io.asm which has all of the definitions for the functions and also a c code file like the one below:
int __attribute__((cdecl)) asm_main( void );
int main() {
int ret_status;
ret_status = asm_main();
return ret_status;
}
print_string:
enter 0,0
pusha
pushf
push eax
push dword string_format
call _printf
pop ecx
pop ecx
popf
popa
leave
ret
I am writing assembly code for my university course and it is not working at all. I have never written code like this before and I'm unsure what I am doing wrong. The code links to a few other codes for different things. Here is the code:
%include "asm_io.inc"
section .data
name_prompt db "Enter your name: ", 0
count_prompt db "Enter the number of repetitions (50-100): ", 0
error_msg db "Error: Number must be between 50 and 100.", 10, 0
welcome_msg db "Welcome, ", 0
newline db 10, 0
section .bss
name resb 128 ; Allocate 128 bytes for the name
num_reps resd 1
section .text
global asm_main ; Declare the function to be used by the C code
extern print_string ; External declarations from asm_io.inc
extern read_char
extern read_int
extern print_nl
asm_main: ; Entry point for the C code
push ebp ; Save the base pointer (set up stack frame)
mov ebp, esp ; Move stack pointer into base pointer
; Prompt for name
push name_prompt
call print_string
add esp, 4 ; Properly clean up the stack after calling print_string
; Read the name character-by-character
lea eax, [name]
call read_char_loop
call print_nl
validate_reps:
; Prompt for number of repetitions
push count_prompt
call print_string
add esp, 4
; Read number of repetitions
call read_int
mov [num_reps], eax
; Validate repetitions (must be between 50 and 100)
cmp eax, 50
jl invalid_reps
cmp eax, 100
jg invalid_reps
; Print welcome message the number of times specified
mov ecx, [num_reps]
print_loop:
cmp ecx, 0
jle end_loop
push welcome_msg
call print_string
add esp, 4
lea eax, [name]
push eax
call print_string
add esp, 4
call print_nl
dec ecx
jmp print_loop
invalid_reps:
push error_msg
call print_string
add esp, 4
call print_nl
jmp validate_reps
end_loop:
; Exit program cleanly using the exit system call
mov eax, 1 ; SYS_exit
xor ebx, ebx ; Status code 0
int 0x80
read_char_loop:
lea edi, [name]
mov ecx, 128
read_next_char:
call read_char
cmp al, 10
je end_read_char
mov [edi], al
inc edi
loop read_next_char
end_read_char:
mov byte [edi], 0
ret
After running a debugger I believe the segmentation fault is happening within the print_string function which is related to the manipulation of the stack and memory access.
Also "asm_io.inc" is this code below:
extern read_int, print_int, print_string
extern read_char, print_char, print_nl
extern sub_dump_regs, sub_dump_mem, sub_dump_math, sub_dump_stack
%macro dump_regs 1
push dword %1
call sub_dump_regs
%endmacro
;
; usage: dump_mem label, start-address, # paragraphs
%macro dump_mem 3
push dword %1
push dword %2
push dword %3
call sub_dump_mem
%endmacro
%macro dump_math 1
push dword %1
call sub_dump_math
%endmacro
%macro dump_stack 3
push dword %3
push dword %2
push dword %1
call sub_dump_stack
%endmacro
I was given that code and also a code called asm_io.asm which has all of the definitions for the functions and also a c code file like the one below:
int __attribute__((cdecl)) asm_main( void );
int main() {
int ret_status;
ret_status = asm_main();
return ret_status;
}
print_string:
enter 0,0
pusha
pushf
push eax
push dword string_format
call _printf
pop ecx
pop ecx
popf
popa
leave
ret
- What command line do you use to compile and link this code? What OS are you using? – Employed Russian Commented Nov 21, 2024 at 15:57
1 Answer
Reset to default 3You pushed the argument to the stack:
push name_prompt
call print_string
whereas print_string is looking for it inside EAX:
push eax
push dword string_format ; assuming a "%s" constant for printf
call _printf
Suggested fix: pass the address of your string in EAX.
Also it seems to me that the function restores the stack after itself, so you should double-check that add esp, 4 is actually needed.
If there is an explanation on how the IO library you are using expects its arguments to be passed, you should look at it again.
本文标签： x86Assembly code not working need help finding the issueStack Overflow
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