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# Create a new segment (pool of memory for allocating chunks from) in the form
# of an *allocation descriptor* that can be passed to the memory allocator
# (defined in a later layer).
#
# Currently an allocation descriptor consists of just the bounds of the pool of
# available memory:
#
# curr: address
# end: address
#
# This isn't enough information to reclaim individual allocations. We can't
# support arbitrary reclamation yet.
== code
# instruction effective address register displacement immediate
# . op subop mod rm32 base index scale r32
# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes
Entry: # manual test
# var ad/ecx: allocation-descriptor
68/push 0/imm32/limit
68/push 0/imm32/curr
89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx
# new-segment(0x1000, ad)
# . . push args
51/push-ecx
68/push 0x1000/imm32
# . . call
e8/call new-segment/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
# var eax: (addr _) = ad->curr
8b/copy 0/mod/indirect 1/rm32/ecx . . . 0/r32/eax . . # copy *ecx to eax
# write to *eax to check that we have access to the newly-allocated segment
c7 0/subop/copy 0/mod/direct 0/rm32/eax . . . . . 0x34/imm32 # copy to *eax
# syscall(exit, eax)
89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx
b8/copy-to-eax 1/imm32/exit
cd/syscall 0x80/imm8
new-segment: # len: int, ad: (addr allocation-descriptor)
# . prologue
55/push-ebp
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# . save registers
50/push-eax
53/push-ebx
# copy len to _mmap-new-segment->len
8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/eax 8/disp8 . # copy *(ebp+8) to eax
89/copy 0/mod/indirect 5/rm32/.disp32 . . 0/r32/eax $_mmap-new-segment:len/disp32 # copy eax to *$_mmap-new-segment:len
# mmap(_mmap-new-segment)
bb/copy-to-ebx _mmap-new-segment/imm32
b8/copy-to-eax 0x5a/imm32/mmap
cd/syscall 0x80/imm8
# copy {eax, eax+len} to *ad
# . ebx = ad
8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 3/r32/ebx 0xc/disp8 . # copy *(ebp+12) to ebx
# . ad->curr = eax
89/copy 0/mod/indirect 3/rm32/ebx . . . 0/r32/eax . . # copy eax to *ebx
# . ad->end = eax+len
03/add 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/eax 8/disp8 . # add *(ebp+8) to eax
89/copy 1/mod/*+disp8 3/rm32/ebx . . . 0/r32/eax 4/disp8 . # copy eax to *(ebx+4)
$new-segment:end:
# . restore registers
5b/pop-to-ebx
58/pop-to-eax
# . epilogue
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
5d/pop-to-ebp
c3/return
== data
# various constants used here were found in the Linux sources (search for file mman-common.h)
_mmap-new-segment: # mmap_arg_struct
# addr
0/imm32
$_mmap-new-segment:len:
# len
0/imm32
# protection flags
3/imm32 # PROT_READ | PROT_WRITE
# sharing flags
0x22/imm32 # MAP_PRIVATE | MAP_ANONYMOUS
# fd
-1/imm32 # since MAP_ANONYMOUS is specified
# offset
0/imm32 # since MAP_ANONYMOUS is specified
# . . vim:nowrap:textwidth=0
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