So I have to do this project for school that consists of reading a file in brainfuck and interpret it as assembly. The code works if I save the file path as a String inside the .data section, but what I want to have it so it gets the file path as an argument when starting the code in the terminal.
I have tried popping 3 times(since the stack should be number of args/ addres of program/ first arg), and then setting %rdi to the value at the adress of the 3rd popped item, but it returns "./interpreter" instead of the file path
This is the code that works:
.data
filePath: .asciz "brainF.b"
fileRead: .asicz "r"
.text
.global main
main:
call fileReader #moves filePath to %rdi, fileRead to %rsi, calls fopen and reads the file
#code that grabs the read string and interprets it
but what I want is:
.data
fileRead: .asciz "r"
.text
.global main
main:
#get 1st argument from terminal(file path) and store it in %rdi
call fileReader #moves fileRead to %rsi, calls fopen and reads the file
and here's how I have to compile and link(this part can't be changed, that's how my teacher wants me to do it):
gcc -o interpreter interpreter.s
./interpreter brainF.b
The 64 bit calling convention passes first 6 function arguments in registers, so argc is in rdi and argv is in rsi. The first command line argument is argv[1] so to access that you need to load 8(%rsi):
.globl main
main:
subq $8, %rsp # align stack
movq 8(%rsi), %rsi # fetch argv[1]
leaq fmt(%rip), %rdi # format string
xorl %eax, %eax # no xmm used
call printf # print
xorl %eax, %eax # zero return value
addq $8, %rsp # restore stack
ret # done
.data
fmt: .string "First argument is %s\n"
$ ./a.out foo bar
First argument is foo
Of course you should check argc to see if you received enough arguments.