Linux上でテキストファイルから文字列を取り込み、文字列内のすべての文字を1ずつシフトし、printf
に出力する32ビットx86 NASMプログラムを作成しようとしています。コンソール。シフトをするのに使われるループ.rot132
とprintf
を除いて、ほとんど全てが機能します。 .rot132
が呼び出されるたびに、segmentation_fault(コアダンプ)が返されます。私はいつmovを行うと思いますかecx, [eax]
何らかのエラーが発生します。どうすればこの部分を克服できますか?アセンブリ言語を変更する入力文字列エラー
;;sddddddddddddddddgsd
[SECTION .data] ; Section containing initialized data
WriteCode db "w",0
OpenCode db "r",0
Filename db "text.txt",0
fileFmt: dd "%c\n",10,0
fileFmt1: dd "%s",10,0
[SECTION .bss] ; Section containing uninitialized data
TextLenght EQU 72 ; Define length of a line of text data
Text resb TextLenght ; Reserve space for disk-based help text line
BUFSIZE EQU 64 ; Define length of text line buffer
Buff resb BUFSIZE+5 ; Reserve space for a line of text
[SECTION .text] ; Section containing code
;; These externals are all from the glibc standard C library:
extern fopen
extern fclose
extern fgets
extern fprintf
extern printf
extern sscanf
extern time
global main ; Required so linker can find entry point
main:
diskhelp:
mov ebx, Filename ; push file name to ebx
push OpenCode ; Push pointer to open-for-read code “r“
push ebx ; Pointer to name of help file is passed in ebx
call fopen ; Attempt to open the file for reading
add esp,8 ; Clean up the stack
cmp eax,0 ; fopen returns null if attempted open failed
jne .disk ; Read help info from disk file...
ret
.disk: mov ebx,eax ; Save handle of opened file in ebx
.rdln: push ebx ; Push file handle on the stack
push dword TextLenght ; Limit line length of text read
push Text ; Push address of text line buffer
call fgets ; Read a line of text from the file
add esp,12 ; Clean up the stack
;cmp eax,0 ; A returned null indicates error or EOF
;jle .rot13 ; If we get 0 in eax, close up & return
;push Text ; Push address of help line on the stack
;call printf ; Call printf to display help line
;add esp,4 ; Clean up the stack
.rot131: ; initial shift and test, this work
mov edx, 0 ; our counter
mov eax, Text ; move string into eax
mov ecx, [eax]; move first char in string into ecx
add ecx, 1 ; shift the char up by 1
push ecx ; push to print
push fileFmt
call printf
add esp, 8 ; clear the stack
inc edx ; increase the counter
.rot132:
inc eax ; shift address of eax into next char
mov ecx, [eax] ; move the char into ecx, replace old char; error ??
add ecx, 1 ; shift the char by 1
push ecx ; print
push fileFmt
call printf
add esp, 8 ; clear the stack
inc edx ;incrase counter
cmp edx,4 ; stop loop after edx = 4
jne .rot132
push ebx ; Push the handle of the file to be closed
call fclose ; Closes the file whose handle is on the stack
add esp,4 ; Clean up the stack
ret ; Go home
GDBデバッグ:.rot132を分解:
0x08048559 <+0>: inc %eax
0x0804855a <+1>: mov (%eax),%ecx
0x0804855c <+3>: add $0x1,%ecx
0x0804855f <+6>: push %ecx
0x08048560 <+7>: push $0x804a035
0x08048565 <+12>: call 0x80483b0 <[email protected]>
0x0804856a <+17>: add $0x8,%esp
0x0804856d <+20>: inc %edx
0x0804856e <+21>: cmp $0x4,%edx
0x08048571 <+24>: jne 0x8048559 <rot132>
0x08048573 <+26>: push %ebx
0x08048574 <+27>: call 0x80483d0 <[email protected]>
0x08048579 <+32>: add $0x4,%esp
0x0804857c <+35>: ret
0x0804857d <+36>: xchg %ax,%ax
0x0804857f <+38>: nop
デバッガでは、エラーが発生したときに表示される内容は何ですか? –
あなたはどのOSを使用していますか? Linux/OSX/BSD/Windows? –
申し訳ありませんが、現在Linuxでnasm x86を使用しています。 –