diff options
Diffstat (limited to 'linux/104new-segment.subx')
| -rw-r--r-- | linux/104new-segment.subx | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/linux/104new-segment.subx b/linux/104new-segment.subx new file mode 100644 index 00000000..4c249abe --- /dev/null +++ b/linux/104new-segment.subx @@ -0,0 +1,88 @@ +# 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 + e8/call syscall_exit/disp32 + +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 + e8/call syscall_mmap/disp32 + # 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 |