I’m trying to simply read a floating point value and print it using assembly x86 64. So, the value for the variable price, which I’m using as the buffer for the c function scanf doesn’t change when I try to print it.
It’ll print the value it was initially set to, so in the case of the code bellow, it prints 0.0, so the scanf function doesn’t properly change the value for price.
To generate the executable, I’m using the command nasm -f elf64 test.asm && gcc -no-pie test.o -o test.
What am I doing wrong?
section .data
price dq 0.0
fmt db "%.1f", 0
section .text
global main
extern printf, scanf
main:
push rbp
mov rbp, rsp
mov rdi, fmt ;scanf first arg, format string
mov rsi, price ;scanf second argument, this variable is supposed to change
mov rax, 0
call scanf
movq xmm0, [precoTinta] ;in float point mode xmm0 holds the value to be printed
mov rdi, fmt
mov rax, 1 ;rax has to be set 1 to float point mode
call printf
leave
ret
>Solution :
The %f formatting specifier calls for a float, not a double. Either use %lf for double precision or adjust price to be a single precision float.