我正在编写一个子例程来使用堆栈将十进制数字简单地重新打印为字符串，但没有得到我期望的值。当我通过调试器运行它时，我发现我无法将 esi 的值获取到 al。我怀疑我不被允许以我现在的方式使用 esi，但我不确定是否可以通过其他方式做到这一点。此外，我不允许将存储在 edx 中的元素压入堆栈。
子程序代码:
%define STDIN 0
%define STDOUT 1
%define SYSCALL_EXIT 1
%define SYSCALL_READ 3
%define SYSCALL_WRITE 4
%define BUFLEN 256
SECTION .bss ; uninitialized data section
src_str: resb BUFLEN ; buffer for backwards number
dec_str: resb BUFLEN ; number will be converted and put in this buffer
rlen: resb 4 ; length
SECTION .text ; code begins here
global prt_dec
; Begin subroutine
prt_dec:
push eax
push ebx
push ecx
push edx
push esi
push edi
mov eax, [esp + 28] ; store the decimal number 4 bytes each for each push, plus the eip
mov esi, src_str ; point esi to the backwards string buffer
mov edi, dec_str ; point edi to the new buffer
mov ebx, 10 ; stores the constant 10 in ebx
div_loop:
mov edx, 0 ; clear out edx
div ebx ; divide the number by 10
add edx, '0' ; convert from decimal to char
mov [esi], edx ; store char in output buffer
inc esi ; move to next spot in output buffer
inc ecx ; keep track of how many chars are added
cmp eax, 0 ; is there anything left to divide into?
jne div_loop ; if so, continue the loop
output_loop:
add esi, ecx ; move 1 element beyond the end of the buffer
mov al, [esi - 1] ; move the last element in the buffer into al
mov [edi], al ; move it into the first position of the converted output buffer
inc edi ; move to the next position of the converted output buffer
dec ecx ; decrement to move backwards through the output buffer
cmp ecx, 0 ; if it doesn't equal 0, continue loop
jne output_loop
print:
mov eax, SYSCALL_WRITE ; write out string
mov ebx, STDOUT
mov ecx, dec_str
mov edx, 0
mov edx, rlen
int 080h
pop_end:
pop edi ; move the saved values back into their original registers
pop esi
pop edx
pop ecx
pop ebx
pop eax
ret
; End subroutine
司机:
%define STDIN 0
%define STDOUT 1
%define SYSCALL_EXIT 1
%define SYSCALL_READ 3
%define SYSCALL_WRITE 4
SECTION .data ; initialized data section
lf: db 10 ; just a linefeed
msg1: db " plus "
len1 equ $ - msg1
msg2: db " minus "
len2 equ $ - msg2
msg3: db " equals "
len3 equ $ - msg3
SECTION .text ; Code section.
global _start ; let loader see entry point
extern prt_dec
_start:
mov ebx, 17
mov edx, 214123
mov edi, 2223187809
mov ebp, 1555544444
push dword 24
call prt_dec
add esp, 4
call prt_lf
push dword 0xFFFFFFFF
call prt_dec
add esp, 4
call prt_lf
push 3413151
call prt_dec
add esp, 4
call prt_lf
push ebx
call prt_dec
add esp, 4
call prt_lf
push edx
call prt_dec
add esp, 4
call prt_lf
push edi
call prt_dec
add esp, 4
call prt_lf
push ebp
call prt_dec
add esp, 4
call prt_lf
push 2
call prt_dec
add esp, 4
mov eax, SYSCALL_WRITE ; write message
mov ebx, STDOUT
mov ecx, msg1
mov edx, len1
int 080h
push 3
call prt_dec
add esp, 4
mov eax, SYSCALL_WRITE ; write message
mov ebx, STDOUT
mov ecx, msg3
mov edx, len3
int 080h
push 5
call prt_dec
add esp, 4
call prt_lf
push 7
call prt_dec
add esp, 4
mov eax, SYSCALL_WRITE ; write message
mov ebx, STDOUT
mov ecx, msg2
mov edx, len2
int 080h
push 4
call prt_dec
add esp, 4
mov eax, SYSCALL_WRITE ; write message
mov ebx, STDOUT
mov ecx, msg3
mov edx, len3
int 080h
push 3
call prt_dec
add esp, 4
call prt_lf
; final exit
;
exit: mov EAX, SYSCALL_EXIT ; exit function
mov EBX, 0 ; exit code, 0=normal
int 080h ; ask kernel to take over
; A subroutine to print a LF, all registers are preserved
prt_lf:
push eax
push ebx
push ecx
push edx
mov eax, SYSCALL_WRITE ; write message
mov ebx, STDOUT
mov ecx, lf
mov edx, 1 ; LF is a single character
int 080h
pop edx
pop ecx
pop ebx
pop eax
ret
最佳答案
我想到的修复(星号表示我确实触及的行)，希望从评论中可以清楚地看到我做了什么:
...
div_loop:
* xor edx, edx ; clear out edx
div ebx ; divide the number by 10
* add dl, '0' ; convert from decimal to char
* mov [esi], dl ; store char in output buffer
inc esi ; move to next spot in output buffer
inc ecx ; keep track of how many chars are added
* test eax,eax ; is there anything left to divide into?
* jnz div_loop ; if so, continue the loop
* ; (jnz is same instruction as jne, but in this context I like "zero" more)
* mov [rlen], ecx ; store number of characters into variable
output_loop:
* ; esi already points beyond last digit, as product of div_loop (removed add)
* dec esi ; point to last/previous digit
mov al, [esi] ; move the char from the div_loop buffer into al
mov [edi], al ; move it into the first position of the converted output buffer
inc edi ; move to the next position of the converted output buffer
dec ecx ; decrement to move backwards through the output buffer
* jnz output_loop ; if it doesn't equal 0, continue loop
print:
mov eax, SYSCALL_WRITE ; write out string
mov ebx, STDOUT
mov ecx, dec_str
* mov edx, [rlen] ; read the number of digits from variable
int 080h
...
关于linux - 组装 NASM x86 - 简单堆栈项目，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39923446/