diff options
| author | Kartik Agaram <vc@akkartik.com> | 2019-07-27 16:01:55 -0700 |
|---|---|---|
| committer | Kartik Agaram <vc@akkartik.com> | 2019-07-27 17:47:59 -0700 |
| commit | 6e1eeeebfb453fa7c871869c19375ce60fbd7413 (patch) | |
| tree | 539c4a3fdf1756ae79770d5c4aaf6366f1d1525e /053new-segment.subx | |
| parent | 8846a7f85cc04b77b2fe8a67b6d317723437b00c (diff) | |
| download | mu-6e1eeeebfb453fa7c871869c19375ce60fbd7413.tar.gz | |
5485 - promote SubX to top-level
Diffstat (limited to '053new-segment.subx')
| -rw-r--r-- | 053new-segment.subx | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/053new-segment.subx b/053new-segment.subx new file mode 100644 index 00000000..83c890ea --- /dev/null +++ b/053new-segment.subx @@ -0,0 +1,90 @@ +# 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 |