lets say i have the following assembly lines
movl $-1, %edi
movl $1, %edx
What exactly am I storing into %edi/%edx registers.
Basically if I were to convert this code into a C program, would I be initalizing some variables to -1 and 1 because that's how I see it and that's where I think I'm getting confused.
I understand that immediate = "some constant" but what does that mean?
There are four ways to load something into a register:
Immediate value - in AT&T assembler, that's using a $number, and it loads that particular value (number) into the register. Note that number doesn't have to be a numeric value, it could be, for example, movl $printf, %eax - this would load the address of the function printf into register eax.
From another register, movl %eax, %edx - we now have eax value copied into edx.
From a fixed memory location, movl myvar, %eax - the contents of myvar is in eax.
From a memory location in another register, movl (%eax), %edx - now, edx has whatever 32-bit value is at the address in eax. Of course, assuming it's actually a "good" memory location - if not, we have a segfault.
If this was C code, the code may loook a bit like this:
1)
int x = 42;
int (*printfunc)(const char *fmt, ...) = printf;
2)
int x = 1;
int y = 2;
...,
x = y; // movl %eax, %edx
3)
int x = myvar;
4)
int x = *myptr;
Edit:
Almost everything that is a "source" for a move instruction can also be a source for arithmetic operations, such as add $3, %eax will be the equivalent in C of x += 3;.
