91 lines
4.5 KiB
Plaintext
91 lines
4.5 KiB
Plaintext
# Create a new segment (pool of memory for allocating chunks from) in the form
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# of an *allocation descriptor* that can be passed to the memory allocator
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# (defined in a later layer).
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#
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# Currently an allocation descriptor consists of just the bounds of the pool of
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# available memory:
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#
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# curr : address
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# end : address
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#
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# This isn't enough information to reclaim individual allocations. We can't
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# support arbitrary reclamation yet.
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== code
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# instruction effective address register displacement immediate
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# . op subop mod rm32 base index scale r32
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# . 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
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Entry: # manual test
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# var ad/ecx : (ref allocation-descriptor)
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68/push 0/imm32/limit
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68/push 0/imm32/curr
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89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx
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# new-segment(0x1000, ad)
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# . . push args
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51/push-ecx
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68/push 0x1000/imm32
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# . . call
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e8/call new-segment/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
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# var eax : (addr _) = ad->curr
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8b/copy 0/mod/indirect 1/rm32/ecx . . . 0/r32/eax . . # copy *ecx to eax
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# write to *eax to check that we have access to the newly-allocated segment
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c7 0/subop/copy 0/mod/direct 0/rm32/eax . . . . . 0x34/imm32 # copy to *eax
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# syscall(exit, eax)
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89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx
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b8/copy-to-eax 1/imm32/exit
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cd/syscall 0x80/imm8
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new-segment: # len : int, ad : (ref allocation-descriptor)
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# . prologue
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55/push-ebp
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89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
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# . save registers
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50/push-eax
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53/push-ebx
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# copy len to _mmap-new-segment->len
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/eax 8/disp8 . # copy *(ebp+8) to eax
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89/copy 0/mod/indirect 5/rm32/.disp32 . . 0/r32/eax $_mmap-new-segment:len/disp32 # copy eax to *$_mmap-new-segment:len
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# mmap(_mmap-new-segment)
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bb/copy-to-ebx _mmap-new-segment/imm32
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b8/copy-to-eax 0x5a/imm32/mmap
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cd/syscall 0x80/imm8
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# copy {eax, eax+len} to *ad
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# . ebx = ad
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 3/r32/ebx 0xc/disp8 . # copy *(ebp+12) to ebx
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# . *ebx = eax
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89/copy 0/mod/indirect 3/rm32/ebx . . . 0/r32/eax . . # copy eax to *ebx
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# . *(ebx+4) = eax+len
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03/add 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/eax 8/disp8 . # add *(ebp+8) to eax
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89/copy 1/mod/*+disp8 3/rm32/ebx . . . 0/r32/eax 4/disp8 . # copy eax to *(ebx+4)
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$new-segment:end:
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# . restore registers
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5b/pop-to-ebx
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58/pop-to-eax
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# . epilogue
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89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
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5d/pop-to-ebp
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c3/return
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== data
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# various constants used here were found in the Linux sources (search for file mman-common.h)
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_mmap-new-segment: # (ref mmap_arg_struct)
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# addr
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0/imm32
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$_mmap-new-segment:len:
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# len
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0/imm32
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# protection flags
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3/imm32 # PROT_READ | PROT_WRITE
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# sharing flags
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0x22/imm32 # MAP_PRIVATE | MAP_ANONYMOUS
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# fd
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-1/imm32 # since MAP_ANONYMOUS is specified
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# offset
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0/imm32 # since MAP_ANONYMOUS is specified
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# . . vim:nowrap:textwidth=0
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