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.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
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