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.ifndef _gc_s_file
_gc_s_file:
.section .bss
_write_region_start:
# begin of the active memory area
cell 0
_write_region_end:
# end of the active memory area (%rsp kinda starts here and goes down
# towars the start)
cell 0
_gc_trigger:
# point in memory where the gc will trigger (we don't necessarily wait for the write region to fill up!)
cell 0
_gc_last_size:
# how much data we evacuated last time
cell 0
_gc_min_alloc:
# minimum possible allocation
cell 0 # tunable constant
_gc_grow_ratio:
# 256th's of the minimal amount of memory increment compared to the
# last time. New minimal amount is compared as:
# (ratio * last size) >> 8
cell 0 # tunable constant
_gc_shrink_ratio:
# 256th's of the ratio of post-gc still-free to-space that should be considered for discarding
cell 0
_gc_region_start:
# in GC, this region is being evacuated and will eventually disappear
cell 0
_gc_region_end:
# end of the disappear region
cell 0
_gc_backup_thunk:
# backup of %rsi so that we can use the register for other nonsense
cell 0
_gc_backup_cont:
# backup of %rbp for same reason
cell 0
.section .text
.macro needs_alloc amount
mov %rsp, %rax
sub _write_region_start, %rax
cmp \amount, %rax
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
#add _gc_region_end, %r14
#sub _gc_region_start, %r14
# check if the desired size isn't greater because of the last gc use
mov _gc_last_size, %rax
mulq _gc_grow_ratio
shr $8, %rax
add _gc_min_alloc, %rax
cmp %r14, %rax
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
cmova %rax, %r14
and $0xfffffffffffffff8, %r14 #align
alloc_goes_mmap:
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_init:
mov %rsi, %r13
movq $0x100000, _gc_min_alloc # must be higher than 2x the biggest thunk possible
movq $0x180, _gc_grow_ratio
movq $0x40, _gc_shrink_ratio
mov $0, %rsp # fake original rsp for first alloc run
mov $_uskel_gc_init_cont, %rsi
jmp _uskel_alloc
_uskel_gc_init_cont:
mov _write_region_start, %rax
mov %rax, _gc_trigger
jmp *%r13
_uskel_gc:
# save what we did before ending up here
mov %rbp, _gc_backup_thunk
mov %rsi, _gc_backup_cont
# first we need a new memory area
mov _write_region_start, %rbx
mov _write_region_end, %rcx
mov %rbx, _gc_region_start
mov %rcx, _gc_region_end
mov $_uskel_gc_evacuate, %rsi
jmp _uskel_alloc
_uskel_gc_evacuate:
# point the writer to the new memory area
mov _write_region_end, %rsp
mov %rsp, %r8 # % r8 is the "last thing that was scavenged"
# start by evacuating the thunk and cont
mov _gc_backup_thunk, %rbp
mov $_uskel_gc_evacuate_cont_thunk, %rsi
jmp _gc_evacuate
_uskel_gc_evacuate_cont_thunk:
mov %rbp, _gc_backup_thunk
mov _gc_backup_cont, %rbp
mov $_uskel_gc_evacuate_cont_cont, %rsi
jmp _gc_evacuate
_uskel_gc_evacuate_cont_cont:
mov %rbp, _gc_backup_cont
# scavenge everything
_uskel_gc_scavenge:
# start at what we wrote last
mov %rsp, %rbp # rbp is the iterator (conveniently)
mov %rsp, %r9 # % r9 stores where we started with this evacuate round
# if the thing is already scavenged, we didn't write anything, mark done.
cmp %rbp, %r8
jbe _uskel_gc_scavenge_end
_uskel_gc_scavenge1:
# if all ok, scavenge one thing (moving %rbp) and recheck
mov (%rbp), %rax
jmp *-020(%rax) # scavenge position in infotable
_gc_scavenge_ret:
cmp %rbp, %r8
ja _uskel_gc_scavenge1
# everything above r9 is now scavenged, continue with next round
mov %r9, %r8 # we started at r9, so that is now "done"
jmp _uskel_gc_scavenge
_uskel_gc_scavenge_end:
# deallocate the old memory region
mov $11, %rax # munmap
mov _gc_region_end, %rsi
mov _gc_region_start, %rdi # addr = gc start
sub %rdi, %rsi # len = gc end - gc start
syscall
# recalculate the gc trigger point
mov %rsp, %rax
sub _write_region_start, %rax
mulq _gc_shrink_ratio
shr $8, %rax
add _write_region_start, %rax
mov %rax, _gc_trigger
# save how much data we actually had at this point
mov _write_region_end, %rax
sub %rsp, %rax
mov %rax, _gc_last_size
# restore what we were doing
mov _gc_backup_thunk, %rbp
mov _gc_backup_cont, %rsi
enter_rbp # for simplicity just restart the thunk
_gc_evacuate:
# check if we are really out of the target region
cmp _write_region_start, %rbp
jb _gc_evacuate_go
cmp _write_region_end, %rbp
jae _gc_evacuate_go
_gc_evacuate_skip:
# if not, let's just jump to cont and leave %rbp as result
jmp *%rsi
_gc_evacuate_go:
# if we should evacuate, jump to the evac routine
mov %rbp, %r10
mov (%rbp), %rax
jmp *-030(%rax)
_gc_evacuate_ret:
# install the indirection
movq $IND_code, 000(%r10)
mov %rbp, 010(%r10)
jmp *%rsi
.endif #_gc_s_file
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