Read and print user input with x86 assembly (GNU/Linux)

Question

I\'m learning x86 assembly on GNU/Linux, and I\'m trying to write a program that reads user input from stdin and prints it on stdout.

The following code does work, b

Answer 1

Here's one way of calculating the length of a string in x86 assembly:

lea esi,[string]
mov ecx,-1    ; Start with ecx = -1
xor eax,eax   ; Clear eax
cld           ; Make scasb scan forward 
repne scasb   ; while (ecx != 0) { ecx--; if (*esi++ == al) break; }
; ecx now contains -1 - (strlen(string) + 1) == -strlen(string) - 2
not ecx       ; Inverting ecx gives us -(-strlen(string) - 2) - 1 == strlen(string) + 1 
dec ecx       ; Subtract 1 to get strlen(string)

This assumes that the string is NUL-terminated ('\0'). If the string uses some other terminator you'll have to initialize al to that value before repne scasb.