1 # Create a new segment (pool of memory for allocating chunks from) in the form 2 # of an *allocation descriptor* that can be passed to the memory allocator 3 # (defined in a later layer). 4 # 5 # Currently an allocation descriptor consists of just the bounds of the pool of 6 # available memory: 7 # 8 # curr : address 9 # end : address 10 # 11 # This isn't enough information to reclaim individual allocations. We can't 12 # support arbitrary reclamation yet. 13 14 == code 15 # instruction effective address register displacement immediate 16 # . op subop mod rm32 base index scale r32 17 # . 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 18 19 Entry: # manual test 20 # var ad/ecx : (ref allocation-descriptor) 21 68/push 0/imm32/limit 22 68/push 0/imm32/curr 23 89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx 24 # new-segment(0x1000, ad) 25 # . . push args 26 51/push-ecx 27 68/push 0x1000/imm32 28 # . . call 29 e8/call new-segment/disp32 30 # . . discard args 31 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 32 # var eax : (addr _) = ad->curr 33 8b/copy 0/mod/indirect 1/rm32/ecx . . . 0/r32/eax . . # copy *ecx to eax 34 # write to *eax to check that we have access to the newly-allocated segment 35 c7 0/subop/copy 0/mod/direct 0/rm32/eax . . . . . 0x34/imm32 # copy to *eax 36 # syscall(exit, eax) 37 89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx 38 b8/copy-to-eax 1/imm32/exit 39 cd/syscall 0x80/imm8 40 41 new-segment: # len : int, ad : (ref allocation-descriptor) 42 # . prologue 43 55/push-ebp 44 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 45 # . save registers 46 50/push-eax 47 53/push-ebx 48 # copy len to _mmap-new-segment->len 49 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/eax 8/disp8 . # copy *(ebp+8) to eax 50 89/copy 0/mod/indirect 5/rm32/.disp32 . . 0/r32/eax $_mmap-new-segment:len/disp32 # copy eax to *$_mmap-new-segment:len 51 # mmap(_mmap-new-segment) 52 bb/copy-to-ebx _mmap-new-segment/imm32 53 b8/copy-to-eax 0x5a/imm32/mmap 54 cd/syscall 0x80/imm8 55 # copy {eax, eax+len} to *ad 56 # . ebx = ad 57 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 3/r32/ebx 0xc/disp8 . # copy *(ebp+12) to ebx 58 # . *ebx = eax 59 89/copy 0/mod/indirect 3/rm32/ebx . . . 0/r32/eax . . # copy eax to *ebx 60 # . *(ebx+4) = eax+len 61 03/add 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/eax 8/disp8 . # add *(ebp+8) to eax 62 89/copy 1/mod/*+disp8 3/rm32/ebx . . . 0/r32/eax 4/disp8 . # copy eax to *(ebx+4) 63 $new-segment:end: 64 # . restore registers 65 5b/pop-to-ebx 66 58/pop-to-eax 67 # . epilogue 68 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 69 5d/pop-to-ebp 70 c3/return 71 72 == data 73 74 # various constants used here were found in the Linux sources (search for file mman-common.h) 75 _mmap-new-segment: # (ref mmap_arg_struct) 76 # addr 77 0/imm32 78 $_mmap-new-segment:len: 79 # len 80 0/imm32 81 # protection flags 82 3/imm32 # PROT_READ | PROT_WRITE 83 # sharing flags 84 0x22/imm32 # MAP_PRIVATE | MAP_ANONYMOUS 85 # fd 86 -1/imm32 # since MAP_ANONYMOUS is specified 87 # offset 88 0/imm32 # since MAP_ANONYMOUS is specified 89 90 # . . vim:nowrap:textwidth=0