flat assembler
Message board for the users of flat assembler.
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chastitywhiterose 19 Oct 2025, 05:19
Chastity's Hexadecimal Tool
This program reads or writes bytes of a file. Read Usage Type 1: (hexdump entire file) ./chastehex file Read Usage Type 2: (read one byte from this address) ./chastehex file address Write Usage: (write one or more bytes to this address) ./chastehex file address byte This works for any file as long as the file already exists to begin with. As usual, back up your files first to avoid losing any data! The purpose of this program is to be able to edit one or more bytes of a file without having to install or load up a graphical hex editor. This also allows for scripting the commands to arbitrarily modify files whenever needed. Code: ;Linux 32-bit Assembly source for chastehex ;A special tool originally written in C but translated to Assembly by hand ;See the original at: https://github.com/chastitywhiterose/chastehex ;assemble with: ; fasm chastehex.asm ; chmod +x chastehex format ELF executable entry main ;the main function of our assembly function, just as if I were writing C. main: mov ebx,1 ;ebx must be 1 to write to standard output ;radix will be 16 because this whole program is about hexadecimal mov [radix],16 ; can choose radix for integer input/output! mov [int_newline],0 ;disable automatic printing of newlines after putint ;we will be manually printing spaces or newlines depending on context ;mov eax,argc_string ;call putstring pop eax ;call putint mov [argc],eax ;save the argument count for later pop eax mov [progname],eax ; save the name of the program ;call putstring dec [argc] ;before we try to get the first argument as a file, we must check if it exists mov eax,[argc] ;call putint ;call putline cmp [argc],0 jnz arg_open_file help_start: mov eax,help call putstring help_end: jmp zero_args arg_open_file: pop eax mov [filename],eax ; save the name of the file we will open to read ;call putstring dec [argc] mov ecx, 2 ; open file in read and write mode mov ebx, [filename] ; filename we created above mov eax, 5 ; invoke SYS_OPEN (kernel opcode 5) int 80h ; call the kernel mov [filedesc],eax ; save the file descriptor number for later use mov [file_offset],0 ;assume the offset is 0,beginning of file mov ebx,1 ;call putint ;show the return of the open call cmp eax,0 jb zero_args ;if eax less than zero error occurred ;check next arg ;mov eax,argc_string ;call putstring mov eax,[argc] ;call putint cmp eax,0 ;if there are no more args after filename, just hexdump it jnz next_arg_address ;but if there are more, jump to the next argument to process it as address hexdump: first_read_bytes_row: mov edx, 0x10 ;number of bytes to read mov ecx, byte_array ;address to store the bytes mov ebx, [filedesc] ;move the opened file descriptor into EBX mov eax, 3 ;invoke SYS_READ (kernel opcode 3) int 80h ;call the kernel mov [bytes_read],eax mov ebx,1 ;switch back ebx to 1 for stdout ; call putint cmp [bytes_read],1 jl file_error ;if less than one bytes read, there is an error jmp file_success file_error: mov eax,[filename] ;call putstring mov eax,[file_offset] mov [int_newline],' ' mov [int_width],8 call putint mov eax,end_of_file_string call putstring call putline jmp zero_args ; this point is reached if file was read from successfully file_success: ;mov eax,[filename] ;call putstring ;mov eax,file_opened_string ;call putstring mov eax,byte_array ;call putstring next_row_of_bytes: mov ebx,1 call print_bytes_row call read_bytes_row add [file_offset],0x10 cmp [bytes_read],1 jl zero_args ;if less than one bytes read, there is an error jmp next_row_of_bytes jmp zero_args ;end program here ; address argument section next_arg_address: ;if there is at least one more arg pop eax ;pop the argument into eax and process it as a hex number dec [argc] call strint ;call putint ; use the hex number as an address to seek to in the file mov edx, 0 ; whence argument (SEEK_SET) mov ecx, eax ; move the file cursor to this address mov ebx, [filedesc] ; move the opened file descriptor into EBX mov eax, 19 ; invoke SYS_LSEEK (kernel opcode 19) int 80h ; call the kernel mov [file_offset],ecx ; move the new offset ;check the number of args still remaining mov eax,argc_string ;call putstring mov eax,[argc] ;call putint ;display number of args left ;call putline cmp eax,0 jnz next_arg_write ; if there are still arguments, skip this read section and enter writing mode read_one_byte: mov edx, 1 ;number of bytes to read mov ecx, byte_array ;address to store the bytes mov ebx, [filedesc] ;move the opened file descriptor into EBX mov eax, 3 ;invoke SYS_READ (kernel opcode 3) int 80h ;call the kernel ;eax will have the number of bytes read after system call cmp eax,1 jz print_byte_info ;if exactly 1 byte was read, proceed to print info ;otherwise, print an EOF message for this address mov eax,[file_offset] mov [int_width],8 call putint call putspace mov eax,end_of_file_string call putstring call putline jmp zero_args ;go to end of program mov eax,end_of_file_string call putstring ;print the address and the byte at that address print_byte_info: mov eax,[file_offset] mov [int_width],8 call putint call putspace mov eax,0 mov al,[byte_array] mov [int_width],2 call putint call putline ;;;;;;;;;; ;this section interprets the rest of the args as bytes to write next_arg_write: cmp [argc],0 jz zero_args pop eax dec [argc] call strint ;try to convert string to a hex number ;write that number as a byte value to the file mov [temp_byte],al mov eax,4 ;invoke SYS_WRITE (kernel opcode 4 on 32 bit systems) mov ebx,[filedesc] ;write to the file (not STDOUT) mov ecx,temp_byte ;pointer to temporary byte address mov edx,1 ;write 1 byte int 80h ;system call to write the message mov eax,[file_offset] inc [file_offset] mov [int_width],8 call putint call putspace mov eax,0 mov al,[temp_byte] mov [int_width],2 call putint call putline ;don't use these except for debugging ;call putstring ;mov eax,int_newline ;call putstring jmp next_arg_write zero_args: ;this is the end of the program ;we close the open file and then use the exit call mov eax, 6 ; invoke SYS_CLOSE (kernel opcode 6) mov ebx,[filedesc] ;file number to close int 80h ; call the kernel mov eax, 1 ; invoke SYS_EXIT (kernel opcode 1) mov ebx, 0 ; return 0 status on exit - 'No Errors' int 80h ;variables for managing arguments argc dd 0 argx dd 0 progname dd 0 ; name of the program filename dd 0 ; name of the file to be opened filedesc dd 0 ; file descriptor bytes_read dd 0 file_offset dd 0 temp_byte db 0 argc_string db 'argc=',0 argx_string db 'argx=',0 file_opened_string db ' was successfully opened!',0Ah,0 file_failed_string db ' could not be opened!',0Ah,0 end_of_file_string db 'EOF',0 help db 'Welcome to chastehex! The tool for reading and writing bytes of a file!',0Ah db 'To hexdump an entire file:',0Ah,9,'chastehex file',0Ah db 'To read a single byte at an address:',0Ah,9,'chastehex file address',0Ah db 'To write a single byte at an address:',0Ah,9,'chastehex file address value',0Ah db 'The file must exist before you launch the program.',0Ah db 'This design was to prevent accidentally opening a mistyped filename.',0Ah,0 ; this is where I keep my string variables main_string db "This is Chastity's 32-bit Assembly Hex Dumper/Editor.",0Ah,0 test_input_string db '11000',0 ;where we will store data from the file byte_array db 32 dup '?',0 print_bytes_row: mov eax,[file_offset] mov [int_width],8 call putint call putspace mov esi,byte_array next_hex: push esi mov ecx,0 mov cl,[esi] mov eax,ecx mov [int_width],2 call putint call putspace pop esi inc esi dec [bytes_read] cmp [bytes_read],0 jnz next_hex call putline ret read_bytes_row: mov edx, 0x10 ; number of bytes to read - one for each letter of the file contents mov ecx, byte_array ; move the memory address of our file contents variable into ecx mov ebx, [filedesc] ; move the opened file descriptor into EBX mov eax, 3 ; invoke SYS_READ (kernel opcode 3) int 80h ; call the kernel mov [bytes_read],eax ret ; These are my string and integer output routines. ; function to print zero terminated string pointed to by register eax stdout dd 1 ; variable for standard output so that it can theoretically be redirected putstring: push eax push ebx push ecx push edx mov edx,eax ; copy eax to edx as well. Now both registers have the address of the main_string putstring_strlen_start: ; this loop finds the lenge of the string as part of the putstring function cmp [edx],byte 0 ; compare byte at address edx with 0 jz strlen_end ; if comparison was zero, jump to loop end because we have found the length inc edx jmp putstring_strlen_start strlen_end: sub edx,eax ; edx will now have correct number of bytes when we use it for the system write call mov ecx,eax ; pointer/address of string to write mov eax, 4 ; invoke SYS_WRITE (kernel opcode 4 on 32 bit systems) mov ebx,[stdout] ; write to the STDOUT file int 80h ; system call to write the message pop edx pop ecx pop ebx pop eax ret ; this is the end of the putstring function return to calling location ;this is the location in memory where digits are written to by the putint function int_string db 32 dup '?' ;enough bytes to hold maximum size 32-bit binary integer ; this is the end of the integer string optional line feed and terminating zero ; clever use of this label can change the ending to be a different character when needed int_newline db 0Ah,0 radix dd 2 ;radix or base for integer output. 2=binary, 8=octal, 10=decimal, 16=hexadecimal int_width dd 8 ;this function creates a string of the integer in eax ;it uses the above radix variable to determine base from 2 to 36 ;it then loads eax with the address of the string ;this means that it can be used with the putstring function intstr: mov ebp,int_newline-1 ;find address of lowest digit(just before the newline 0Ah) mov ecx,1 digits_start: mov edx,0; mov esi,[radix] ;radix is from memory location just before this function div esi cmp edx,10 jb decimal_digit jge hexadecimal_digit decimal_digit: ;we go here if it is only a digit 0 to 9 add edx,'0' jmp save_digit hexadecimal_digit: sub edx,10 add edx,'A' save_digit: mov [ebp],dl cmp eax,0 jz intstr_end dec ebp inc ecx jmp digits_start intstr_end: prefix_zeros: cmp ecx,[int_width] jnb end_zeros dec ebp mov [ebp],byte '0' inc ecx jmp prefix_zeros end_zeros: mov eax,ebp ; now that the digits have been written to the string, display it! ret ; function to print string form of whatever integer is in eax ; The radix determines which number base the string form takes. ; Anything from 2 to 36 is a valid radix ; in practice though, only bases 2,8,10,and 16 will make sense to other programmers ; this function does not process anything by itself but calls the combination of my other ; functions in the order I intended them to be used. putint: push eax push ebx push ecx push edx call intstr call putstring pop edx pop ecx pop ebx pop eax ret ;this function converts a string pointed to by eax into an integer returned in eax instead ;it is a little complicated because it has to account for whether the character in ;a string is a decimal digit 0 to 9, or an alphabet character for bases higher than ten ;it also checks for both uppercase and lowercase letters for bases 11 to 36 ;finally, it checks if that letter makes sense for the base. ;For example, G to Z cannot be used in hexadecimal, only A to F can ;The purpose of writing this function was to be able to accept user input as integers strint: mov esi,eax ;copy string address from eax to esi because eax will be replaced soon! mov eax,0 read_strint: mov ecx,0 ; zero ecx so only lower 8 bits are used mov cl,[esi] inc esi cmp cl,0 ; compare byte at address edx with 0 jz strint_end ; if comparison was zero, this is the end of string ;if char is below '0' or above '9', it is outside the range of these and is not a digit cmp cl,'0' jb not_digit cmp cl,'9' ja not_digit ;but if it is a digit, then correct and process the character is_digit: sub cl,'0' jmp process_char not_digit: ;it isn't a digit, but it could be perhaps and alphabet character ;which is a digit in a higher base ;if char is below 'A' or above 'Z', it is outside the range of these and is not capital letter cmp cl,'A' jb not_upper cmp cl,'Z' ja not_upper is_upper: sub cl,'A' add cl,10 jmp process_char not_upper: ;if char is below 'a' or above 'z', it is outside the range of these and is not lowercase letter cmp cl,'a' jb not_lower cmp cl,'z' ja not_lower is_lower: sub cl,'a' add cl,10 jmp process_char not_lower: ;if we have reached this point, result invalid and end function jmp strint_end process_char: cmp ecx,[radix] ;compare char with radix jae strint_end ;if this value is above or equal to radix, it is too high despite being a valid digit/alpha mov edx,0 ;zero edx because it is used in mul sometimes mul [radix] ;mul eax with radix add eax,ecx jmp read_strint ;jump back and continue the loop if nothing has exited it strint_end: ret ;the next utility functions simply print a space or a newline ;these help me save code when printing lots of things for debugging space db ' ',0 line db 0Dh,0Ah,0 putspace: push eax mov eax,space call putstring pop eax ret putline: push eax mov eax,line call putstring pop eax ret
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Mаt Quasar 19 Oct 2025, 07:40
Your source code missing this line?
Code: segment readable executable |
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macomics 19 Oct 2025, 10:02
Mаt Quasar wrote: Your source code missing this line? This segment is created by default for the elf file. |
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Tomasz Grysztar 19 Oct 2025, 10:06
The segment that is created by default also has the WRITEABLE attribute in addition to READABLE and EXECUTABLE, and obviously when you replace it with one that does not have it, the code is going to segfault unless you move all the data (the one you write to, at least) to a separate writable segment.
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macomics 19 Oct 2025, 10:10
Your segment declaration code. I added only the lines of the segments and rearranged the existing ones in the correct order.
Code: $ fasm test.asm flat assembler version 1.73.32 (16384 kilobytes memory, x64) 4 passes, 1700 bytes. ~ $ ./test Welcome to chastehex! The tool for reading and writing bytes of a file! To hexdump an entire file: chastehex file To read a single byte at an address: chastehex file address To write a single byte at an address: chastehex file address value The file must exist before you launch the program. This design was to prevent accidentally opening a mistyped filename. Code: ;Linux 32-bit Assembly source for chastehex ;A special tool originally written in C but translated to Assembly by hand ;See the original at: https://github.com/chastitywhiterose/chastehex ;assemble with: ; fasm chastehex.asm ; chmod +x chastehex format ELF executable segment executable entry main ;the main function of our assembly function, just as if I were writing C. main: mov ebx,1 ;ebx must be 1 to write to standard output ;radix will be 16 because this whole program is about hexadecimal mov [radix],16 ; can choose radix for integer input/output! mov [int_newline],0 ;disable automatic printing of newlines after putint ;we will be manually printing spaces or newlines depending on context ;mov eax,argc_string ;call putstring pop eax ;call putint mov [argc],eax ;save the argument count for later pop eax mov [progname],eax ; save the name of the program ;call putstring dec [argc] ;before we try to get the first argument as a file, we must check if it exists mov eax,[argc] ;call putint ;call putline cmp [argc],0 jnz arg_open_file help_start: mov eax,help call putstring help_end: jmp zero_args arg_open_file: pop eax mov [filename],eax ; save the name of the file we will open to read ;call putstring dec [argc] mov ecx, 2 ; open file in read and write mode mov ebx, [filename] ; filename we created above mov eax, 5 ; invoke SYS_OPEN (kernel opcode 5) int 80h ; call the kernel mov [filedesc],eax ; save the file descriptor number for later use mov [file_offset],0 ;assume the offset is 0,beginning of file mov ebx,1 ;call putint ;show the return of the open call cmp eax,0 jb zero_args ;if eax less than zero error occurred ;check next arg ;mov eax,argc_string ;call putstring mov eax,[argc] ;call putint cmp eax,0 ;if there are no more args after filename, just hexdump it jnz next_arg_address ;but if there are more, jump to the next argument to process it as address hexdump: first_read_bytes_row: mov edx, 0x10 ;number of bytes to read mov ecx, byte_array ;address to store the bytes mov ebx, [filedesc] ;move the opened file descriptor into EBX mov eax, 3 ;invoke SYS_READ (kernel opcode 3) int 80h ;call the kernel mov [bytes_read],eax mov ebx,1 ;switch back ebx to 1 for stdout ; call putint cmp [bytes_read],1 jl file_error ;if less than one bytes read, there is an error jmp file_success file_error: mov eax,[filename] ;call putstring mov eax,[file_offset] mov [int_newline],' ' mov [int_width],8 call putint mov eax,end_of_file_string call putstring call putline jmp zero_args ; this point is reached if file was read from successfully file_success: ;mov eax,[filename] ;call putstring ;mov eax,file_opened_string ;call putstring mov eax,byte_array ;call putstring next_row_of_bytes: mov ebx,1 call print_bytes_row call read_bytes_row add [file_offset],0x10 cmp [bytes_read],1 jl zero_args ;if less than one bytes read, there is an error jmp next_row_of_bytes jmp zero_args ;end program here ; address argument section next_arg_address: ;if there is at least one more arg pop eax ;pop the argument into eax and process it as a hex number dec [argc] call strint ;call putint ; use the hex number as an address to seek to in the file mov edx, 0 ; whence argument (SEEK_SET) mov ecx, eax ; move the file cursor to this address mov ebx, [filedesc] ; move the opened file descriptor into EBX mov eax, 19 ; invoke SYS_LSEEK (kernel opcode 19) int 80h ; call the kernel mov [file_offset],ecx ; move the new offset ;check the number of args still remaining mov eax,argc_string ;call putstring mov eax,[argc] ;call putint ;display number of args left ;call putline cmp eax,0 jnz next_arg_write ; if there are still arguments, skip this read section and enter writing mode read_one_byte: mov edx, 1 ;number of bytes to read mov ecx, byte_array ;address to store the bytes mov ebx, [filedesc] ;move the opened file descriptor into EBX mov eax, 3 ;invoke SYS_READ (kernel opcode 3) int 80h ;call the kernel ;eax will have the number of bytes read after system call cmp eax,1 jz print_byte_info ;if exactly 1 byte was read, proceed to print info ;otherwise, print an EOF message for this address mov eax,[file_offset] mov [int_width],8 call putint call putspace mov eax,end_of_file_string call putstring call putline jmp zero_args ;go to end of program mov eax,end_of_file_string call putstring ;print the address and the byte at that address print_byte_info: mov eax,[file_offset] mov [int_width],8 call putint call putspace mov eax,0 mov al,[byte_array] mov [int_width],2 call putint call putline ;;;;;;;;;; ;this section interprets the rest of the args as bytes to write next_arg_write: cmp [argc],0 jz zero_args pop eax dec [argc] call strint ;try to convert string to a hex number ;write that number as a byte value to the file mov [temp_byte],al mov eax,4 ;invoke SYS_WRITE (kernel opcode 4 on 32 bit systems) mov ebx,[filedesc] ;write to the file (not STDOUT) mov ecx,temp_byte ;pointer to temporary byte address mov edx,1 ;write 1 byte int 80h ;system call to write the message mov eax,[file_offset] inc [file_offset] mov [int_width],8 call putint call putspace mov eax,0 mov al,[temp_byte] mov [int_width],2 call putint call putline ;don't use these except for debugging ;call putstring ;mov eax,int_newline ;call putstring jmp next_arg_write zero_args: ;this is the end of the program ;we close the open file and then use the exit call mov eax, 6 ; invoke SYS_CLOSE (kernel opcode 6) mov ebx,[filedesc] ;file number to close int 80h ; call the kernel mov eax, 1 ; invoke SYS_EXIT (kernel opcode 1) mov ebx, 0 ; return 0 status on exit - 'No Errors' int 80h print_bytes_row: mov eax,[file_offset] mov [int_width],8 call putint call putspace mov esi,byte_array next_hex: push esi mov ecx,0 mov cl,[esi] mov eax,ecx mov [int_width],2 call putint call putspace pop esi inc esi dec [bytes_read] cmp [bytes_read],0 jnz next_hex call putline ret read_bytes_row: mov edx, 0x10 ; number of bytes to read - one for each letter of the file contents mov ecx, byte_array ; move the memory address of our file contents variable into ecx mov ebx, [filedesc] ; move the opened file descriptor into EBX mov eax, 3 ; invoke SYS_READ (kernel opcode 3) int 80h ; call the kernel mov [bytes_read],eax ret ; These are my string and integer output routines. ; function to print zero terminated string pointed to by register eax putstring: push eax push ebx push ecx push edx mov edx,eax ; copy eax to edx as well. Now both registers have the address of the main_string putstring_strlen_start: ; this loop finds the lenge of the string as part of the putstring function cmp [edx],byte 0 ; compare byte at address edx with 0 jz strlen_end ; if comparison was zero, jump to loop end because we have found the length inc edx jmp putstring_strlen_start strlen_end: sub edx,eax ; edx will now have correct number of bytes when we use it for the system write call mov ecx,eax ; pointer/address of string to write mov eax, 4 ; invoke SYS_WRITE (kernel opcode 4 on 32 bit systems) mov ebx,[stdout] ; write to the STDOUT file int 80h ; system call to write the message pop edx pop ecx pop ebx pop eax ret ; this is the end of the putstring function return to calling location ;this function creates a string of the integer in eax ;it uses the above radix variable to determine base from 2 to 36 ;it then loads eax with the address of the string ;this means that it can be used with the putstring function intstr: mov ebp,int_newline-1 ;find address of lowest digit(just before the newline 0Ah) mov ecx,1 digits_start: mov edx,0; mov esi,[radix] ;radix is from memory location just before this function div esi cmp edx,10 jb decimal_digit jge hexadecimal_digit decimal_digit: ;we go here if it is only a digit 0 to 9 add edx,'0' jmp save_digit hexadecimal_digit: sub edx,10 add edx,'A' save_digit: mov [ebp],dl cmp eax,0 jz intstr_end dec ebp inc ecx jmp digits_start intstr_end: prefix_zeros: cmp ecx,[int_width] jnb end_zeros dec ebp mov [ebp],byte '0' inc ecx jmp prefix_zeros end_zeros: mov eax,ebp ; now that the digits have been written to the string, display it! ret ; function to print string form of whatever integer is in eax ; The radix determines which number base the string form takes. ; Anything from 2 to 36 is a valid radix ; in practice though, only bases 2,8,10,and 16 will make sense to other programmers ; this function does not process anything by itself but calls the combination of my other ; functions in the order I intended them to be used. putint: push eax push ebx push ecx push edx call intstr call putstring pop edx pop ecx pop ebx pop eax ret ;this function converts a string pointed to by eax into an integer returned in eax instead ;it is a little complicated because it has to account for whether the character in ;a string is a decimal digit 0 to 9, or an alphabet character for bases higher than ten ;it also checks for both uppercase and lowercase letters for bases 11 to 36 ;finally, it checks if that letter makes sense for the base. ;For example, G to Z cannot be used in hexadecimal, only A to F can ;The purpose of writing this function was to be able to accept user input as integers strint: mov esi,eax ;copy string address from eax to esi because eax will be replaced soon! mov eax,0 read_strint: mov ecx,0 ; zero ecx so only lower 8 bits are used mov cl,[esi] inc esi cmp cl,0 ; compare byte at address edx with 0 jz strint_end ; if comparison was zero, this is the end of string ;if char is below '0' or above '9', it is outside the range of these and is not a digit cmp cl,'0' jb not_digit cmp cl,'9' ja not_digit ;but if it is a digit, then correct and process the character is_digit: sub cl,'0' jmp process_char not_digit: ;it isn't a digit, but it could be perhaps and alphabet character ;which is a digit in a higher base ;if char is below 'A' or above 'Z', it is outside the range of these and is not capital letter cmp cl,'A' jb not_upper cmp cl,'Z' ja not_upper is_upper: sub cl,'A' add cl,10 jmp process_char not_upper: ;if char is below 'a' or above 'z', it is outside the range of these and is not lowercase letter cmp cl,'a' jb not_lower cmp cl,'z' ja not_lower is_lower: sub cl,'a' add cl,10 jmp process_char not_lower: ;if we have reached this point, result invalid and end function jmp strint_end process_char: cmp ecx,[radix] ;compare char with radix jae strint_end ;if this value is above or equal to radix, it is too high despite being a valid digit/alpha mov edx,0 ;zero edx because it is used in mul sometimes mul [radix] ;mul eax with radix add eax,ecx jmp read_strint ;jump back and continue the loop if nothing has exited it strint_end: ret putspace: push eax mov eax,space call putstring pop eax ret putline: push eax mov eax,line call putstring pop eax ret segment writeable stdout dd 1 ; variable for standard output so that it can theoretically be redirected ;this is the location in memory where digits are written to by the putint function int_string db 32 dup '?' ;enough bytes to hold maximum size 32-bit binary integer ; this is the end of the integer string optional line feed and terminating zero ; clever use of this label can change the ending to be a different character when needed int_newline db 0Ah,0 radix dd 2 ;radix or base for integer output. 2=binary, 8=octal, 10=decimal, 16=hexadecimal int_width dd 8 ;variables for managing arguments argc dd 0 argx dd 0 progname dd 0 ; name of the program filename dd 0 ; name of the file to be opened filedesc dd 0 ; file descriptor bytes_read dd 0 file_offset dd 0 temp_byte db 0 argc_string db 'argc=',0 argx_string db 'argx=',0 file_opened_string db ' was successfully opened!',0Ah,0 file_failed_string db ' could not be opened!',0Ah,0 end_of_file_string db 'EOF',0 help db 'Welcome to chastehex! The tool for reading and writing bytes of a file!',0Ah db 'To hexdump an entire file:',0Ah,9,'chastehex file',0Ah db 'To read a single byte at an address:',0Ah,9,'chastehex file address',0Ah db 'To write a single byte at an address:',0Ah,9,'chastehex file address value',0Ah db 'The file must exist before you launch the program.',0Ah db 'This design was to prevent accidentally opening a mistyped filename.',0Ah,0 ; this is where I keep my string variables main_string db "This is Chastity's 32-bit Assembly Hex Dumper/Editor.",0Ah,0 test_input_string db '11000',0 ;where we will store data from the file byte_array db 32 dup '?',0 ;the next utility functions simply print a space or a newline ;these help me save code when printing lots of things for debugging space db ' ',0 line db 0Dh,0Ah,0 |
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chastitywhiterose 19 Oct 2025, 11:39
I see what you did there. I really do need to learn about the segments but it always assembled and ran for me fine the way I had it. I use this as my makefile
Code: main-fasm: fasm main.asm chmod +x main ./main Originally I had the functions in separate files based on category with each data element being between functions. Each variable was placed before the function which first uses is. But I can see how the rearranged version you made of my code might be more readable to other people. This is the largest project I have ever attempted in Assembly so a little organization is good! |
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chastitywhiterose 19 Oct 2025, 11:42
Tomasz Grysztar wrote: The segment that is created by default also has the WRITEABLE attribute in addition to READABLE and EXECUTABLE, and obviously when you replace it with one that does not have it, the code is going to segfault unless you move all the data (the one you write to, at least) to a separate writable segment. That makes sense. The reason I always use FASM is because it doesn't force me into declaring segments. Do you think different segments are good or did you write FASM to make the default segment readable,writeable, and executable because you didn't want to have to deal with that complexity? |
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