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: 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 #? e8/call syscall_exit/disp32 39 40 new-segment: # len: int, ad: (addr allocation-descriptor) 41 # . prologue 42 55/push-ebp 43 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 44 # . save registers 45 50/push-eax 46 53/push-ebx 47 # copy len to _mmap-new-segment->len 48 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/eax 8/disp8 . # copy *(ebp+8) to eax 49 89/copy 0/mod/indirect 5/rm32/.disp32 . . 0/r32/eax $_mmap-new-segment:len/disp32 # copy eax to *$_mmap-new-segment:len 50 # mmap(_mmap-new-segment) 51 bb/copy-to-ebx _mmap-new-segment/imm32 52 e8/call syscall_mmap/disp32 53 # copy {eax, eax+len} to *ad 54 # . ebx = ad 55 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 3/r32/ebx 0xc/disp8 . # copy *(ebp+12) to ebx 56 # . ad->curr = eax 57 89/copy 0/mod/indirect 3/rm32/ebx . . . 0/r32/eax . . # copy eax to *ebx 58 # . ad->end = eax+len 59 03/add 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/eax 8/disp8 . # add *(ebp+8) to eax 60 89/copy 1/mod/*+disp8 3/rm32/ebx . . . 0/r32/eax 4/disp8 . # copy eax to *(ebx+4) 61 $new-segment:end: 62 # . restore registers 63 5b/pop-to-ebx 64 58/pop-to-eax 65 # . epilogue 66 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 67 5d/pop-to-ebp 68 c3/return 69 70 == data 71 72 # various constants used here were found in the Linux sources (search for file mman-common.h) 73 _mmap-new-segment: # mmap_arg_struct 74 # addr 75 0/imm32 76 $_mmap-new-segment:len: 77 # len 78 0/imm32 79 # protection flags 80 3/imm32 # PROT_READ | PROT_WRITE 81 # sharing flags 82 0x22/imm32 # MAP_PRIVATE | MAP_ANONYMOUS 83 # fd 84 -1/imm32 # since MAP_ANONYMOUS is specified 85 # offset 86 0/imm32 # since MAP_ANONYMOUS is specified 87 88 # . . vim:nowrap:textwidth=0