strlen的汇编 [英] strlen in assembly
问题描述
我做了我自己实现strlen的汇编,但它不会返回正确的值。它返回字符串的长度+ 4,因此。我不明白为什么..我希望任何你...
大会来源:
I made my own implementation of strlen in assembly, but it doesn't return the correct value. It returns the string length + 4. Consequently. I don't see why.. and I hope any of you do...
Assembly source:
section .text
[GLOBAL stringlen:] ; C function
stringlen:
push ebp
mov ebp, esp ; setup the stack frame
mov ecx, [ebp+8]
xor eax, eax ; loop counter
startLoop:
xor edx, edx
mov edx, [ecx+eax]
inc eax
cmp edx, 0x0 ; null byte
jne startLoop
end:
pop ebp
ret
和主程序:
#include <stdio.h>
extern int stringlen(char *);
int main(void)
{
printf("%d", stringlen("h"));
return 0;
}
感谢
推荐答案
您没有访问字节数(字),但双字。所以,你的code是不是找一个终止零,它正在寻找连续4零。请注意,不会总是返回正确的值+4,这取决于你的字符串后,存储器包含。
You are not accessing bytes (characters), but doublewords. So your code is not looking for a single terminating zero, it is looking for 4 consecutive zeroes. Note that won't always return correct value +4, it depends on what the memory after your string contains.
要解决,你应该使用字节访问,例如通过改变 EDX
到 DL
。
To fix, you should use byte accesses, for example by changing edx
to dl
.
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