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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 : (address allocation-descriptor) = {0, 0}
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
# EAX = 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 : (address allocation-descriptor)
# . prolog
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
# . *EBX = EAX
89/copy 0/mod/indirect 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to *EBX
# . *(EBX+4) = 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
# . epilog
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: # type 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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