.ifndef _gc_s_file
_gc_s_file:

.macro prealloc name amount
	mov %rsp,%rax
	sub _write_region_start, %rax
	cmp $amount, %rax #TODO check direction
	jb _uskel_gc
.endm

_uskel_alloc:
	mov %rsi, %r15 # %rsi is the return address; back it up

	# calculate the desired size to %r14
	mov _gc_min_alloc, %r14

	# check if the desired size isn't greater because of the last gc use
	mov _gc_last_size, %rax
	mul _gc_min_expect_ratio, %rax
	shr 8, %rax
	cmp %r14, %rax #TODO check direction
	cmova %rax, %r14

	# check if we don't need even more space because we need to evacuate stuff
	mov _gc_region_end, %rax
	sub %rsp, %rax # trick -- if we counted from gc region start, allocated memory could never shrink
	cmp %r14, %rax #TODO direction
	cmova %rax, %r14
	#TODO add functionality to trigger the gc's a bit earlier than when
	# they hit _write_region_start, to allow for faster compaction.
	# maybe _write_region_trigger = 25%ish between _write_region_start and %rsp ?

	mov $9, %rax # mmap
	mov $0, %rdi # addr = NULL
	mov %r14, %rsi # len = %r14
	mov $0b11, %rdx # prot = PROT_READ 0b1 | PROT_WRITE 0b10
	mov $0x22, %r10 # flags = MAP_PRIVATE 0x2 | MAP_ANONYMOUS 0x20
	mov $-1, %r8 # fd = -1
	mov $0, %r9 # off = 0
	syscall

	# store the results
	mov %rax, _write_region_start
	add %r14, %rax
	mov %rax, _write_region_end
	mov %rax, %rsp # initialize writing into the new region

	jmp *%r15

_uskel_gc:
	mov %rbp, _gc_backup_thunk
	mov %rsi, _gc_backup_cont
	# first we need a new memory area
	mov _write_region_start, _gc_region_start
	mov _write_region_end, _gc_region_end
	mov $_uskel_gc_evacuate, %r15
	jmp _uskel_alloc
	_uskel_gc_evacuate:
	# we may also need a scavenging queue! Or can that be solved by walking the write region?
	# plan:
	# evacuate thunk and cont, save them right away in _gc_backup_thunk and _cont
	# scavenge from the top of the gc region, evacuating stuff en route
	# (this is a little more complex because we grow down, so we have to
	# scavenge up from %rsp to the last known scavenged position)
	# finish when scavenge doesn't have anything more to scavenge

	# save how much data we actually had at this point
	mov _write_region_end, _gc_last_size
	sub %rsp, _gc_last_size

	enter_rbp # restart the thunk for simplicity

.endif #_gc_s_file