os/arch/i686/interrupts/syscall.s

.extern _syscall

.section .bss, "aw", @nobits
.align 16
syscall_stack_bottom:
.skip (1 << 16) # 16 KiB
syscall_stack_top:

.section .text
.global syscall
syscall:
mov $0x10, %edx
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs

mov %esp, %edx

mov $syscall_stack_top, %esp
push 0x10(%edx)
push 0x0C(%edx)
push 0x08(%edx)
push 0x04(%edx)
push 0x00(%edx)

push %ecx
push %ebx
push %eax

call _syscall

pop %eax
pop %ebx
pop %ecx
iret