.text
.global main
// code for main
main:
push %r13
push %r14
push %r15
pushq $2
call show
pop %r15
pop %r14
pop %r13
mov $0,%rax
ret
// code for show
show:
popq x
pushq x
popq gen
lea genfmt_(%rip),%rdi
movq gen(%rip),%rsi
.extern printf
call printf
ret
.data
gen: .quad 0
genfmt_: .byte '%','u',10,0
x: .quad 0
The title pretty much sums it up. I have no idea why this is generating a segmentation fault error. From my understanding the stack pointer is aligned when I push r15,r14,r13 I then keep it aligned before calling print f. I'm new to assembly so any help is appreciated!
show:
popq x
is an obvious bug. The first thing on the stack on entry to a function is a return address. You're going to have a problem when you try to ret since you've clobbered the return address.
Also, the standard calling convention / ABI for 64bit code passes args in registers, so you're not passing sensible args to printf. (You can pass args between your own asm functions however you like, as long as you don't want to call them from C.)
See the x86 tag wiki for more docs on calling conventions. Also for info on using a debugger, which would have let you ask a better question (by showing which instruction generated the segfault, and what address it was trying to access.)