429 lines
23 KiB
Plaintext
429 lines
23 KiB
Plaintext
# A sketch of Mu-style handles or kinda-safe pointers, that add a modicum of
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# checking to dynamically allocated memory.
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#
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# This approach avoids using 'allocate' directly in favor of two primitives:
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# - 'new', which allocates some space (the 'payload'), stores the address
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# along with an opaque 'alloc id' in a 'handle', and prepends the same
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# alloc id to the payload.
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# - 'lookup', which checks that the alloc id at the start of a handle matches
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# the alloc id at the start of the payload before returning the address.
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#
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# Layout of a handle:
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# offset 0: alloc id
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# offset 4: address
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#
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# To run:
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# $ ./subx translate init.linux 0*.subx apps/handle.subx -o apps/handle
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# $ ./subx run apps/handle
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# Expected result is a successful lookup followed by a hard abort:
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# lookup succeeded
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# lookup failed
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# (This file is a prototype. The 'tests' in it aren't real; failures are
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# expected.)
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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:
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# initialize heap
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# . Heap = new-segment(Heap-size)
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# . . push args
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68/push Heap/imm32
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ff 6/subop/push 0/mod/indirect 5/rm32/.disp32 . . . Heap-size/disp32 # push *Heap-size
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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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e8/call run-tests/disp32 # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'.
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$handle-main:end:
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# syscall(exit, Num-test-failures)
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8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/ebx Num-test-failures/disp32 # copy *Num-test-failures 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: # ad : (addr allocation-descriptor), n : int, out : (handle _)
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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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51/push-ecx
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52/push-edx
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# ecx = n+4
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 1/r32/ecx 0xc/disp8 . # copy *(ebp+12) to ecx
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81 0/subop/add 3/mod/direct 1/rm32/ecx . . . . . 4/imm32 # add to ecx
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# var eax : (handle _) = allocate(ad, ecx)
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# . . push args
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51/push-ecx
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ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8)
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# . . call
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e8/call allocate/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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# edx = out
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 2/r32/edx 0x10/disp8 . # copy *(ebp+16) to edx
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# out->address = eax
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89/copy 1/mod/*+disp8 2/rm32/edx . . . 0/r32/eax 4/disp8 . # copy eax to *(edx+4)
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# if (eax == 0) out->alloc_id = 0, return
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3d/compare-eax-and 0/imm32
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75/jump-if-not-equal $new:continue/disp8
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c7 0/subop/copy 0/mod/indirect 2/rm32/edx . . . . . 0/imm32 # copy to *edx
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eb/jump $new:end/disp8
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$new:continue:
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# otherwise:
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# ecx = *Next-alloc-id
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8b/copy 0/mod/indirect 5/rm32/.disp32 . . 1/r32/ecx Next-alloc-id/disp32 # copy *Next-alloc-id to ecx
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# *eax = *Next-alloc-id/ecx
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89/copy 0/mod/indirect 0/rm32/eax . . . 1/r32/ecx . . # copy ecx to *eax
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# out->alloc_id = *Next-alloc-id
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89/copy 0/mod/indirect 2/rm32/edx . . . 1/r32/ecx . . # copy ecx to *edx
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# increment *Next-alloc-id
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ff 0/subop/increment 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 # increment *Next-alloc-id
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$new:end:
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# . restore registers
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5a/pop-to-edx
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59/pop-to-ecx
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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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test-new:
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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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# var heap/edx : (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 2/rm32/edx . . . 4/r32/esp . . # copy esp to edx
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# heap = new-segment(512)
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# . . push args
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52/push-edx
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68/push 0x200/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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# *Next-alloc-id = 0x34
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c7 0/subop/copy 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 0x34/imm32 # copy to *Next-alloc-id
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# var handle/ecx : (ref handle)
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68/push 0/imm32/address
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68/push 0/imm32/alloc-id
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89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx
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# new(heap, 2, handle/ecx)
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# . . push args
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51/push-ecx
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68/push 2/imm32/size
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52/push-edx
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# . . call
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e8/call new/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# check-ints-equal(handle->alloc_id, 0x34, msg)
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# . . push args
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68/push "F - test-new: alloc id of handle"/imm32
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68/push 0x34/imm32
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ff 6/subop/push 0/mod/indirect 1/rm32/ecx . . . . . . # push *ecx
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# check-ints-equal(*handle->address, 0x34, msg)
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# . . push args
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68/push "F - test-new: alloc id of payload"/imm32
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68/push 0x34/imm32
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8b/copy 1/mod/*+disp8 1/rm32/ecx . . . 2/r32/edx 4/disp8 . # copy *(ecx+4) to edx
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ff 6/subop/push 0/mod/indirect 2/rm32/edx . . . . . . # push *edx
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# check-ints-equal(*Next-alloc-id, 0x35)
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# . . push args
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68/push "F - test-new: next alloc id"/imm32
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68/push 0x35/imm32
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ff 6/subop/push 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 # copy to *Next-alloc-id
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# clean up
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# . *Next-alloc-id = 1
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c7 0/subop/copy 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 1/imm32 # copy to *Next-alloc-id
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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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_pending-test-new-failure:
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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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# . *Next-alloc-id = 0x34
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c7 0/subop/copy 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 0x34/imm32 # copy to *Next-alloc-id
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# define an allocation-descriptor with no space left
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# . var ad/eax : (ref allocation-descriptor) = {0x10, 0x10}
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68/push 0x10/imm32/limit
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68/push 0x10/imm32/curr
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89/copy 3/mod/direct 0/rm32/eax . . . 4/r32/esp . . # copy esp to eax
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# . var handle/ecx = {random, random}
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68/push 1234/imm32/address
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68/push 5678/imm32/alloc-id
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89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx
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# try to allocate
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# . new(ad, 2, handle/ecx)
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# . . push args
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51/push-ecx
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68/push 2/imm32/size
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50/push-eax
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# . . call
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e8/call new/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# handle should be cleared
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# . check-ints-equal(handle->alloc_id, 0, msg)
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# . . push args
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68/push "F - test-new-failure: alloc id of handle"/imm32
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68/push 0/imm32
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ff 6/subop/push 0/mod/indirect 1/rm32/ecx . . . . . . # push *ecx
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# . check-ints-equal(handle->address, 0, msg)
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# . . push args
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68/push "F - test-new-failure: address of handle"/imm32
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68/push 0/imm32
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ff 6/subop/push 1/mod/*+disp8 1/rm32/ecx . . . . 4/disp8 . # push *(ecx+4)
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# Next-alloc-id should be unmodified
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# . check-ints-equal(*Next-alloc-id, 0x34)
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# . . push args
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68/push "F - test-new-failure: next alloc id"/imm32
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68/push 0x34/imm32
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ff 6/subop/push 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 # copy to *Next-alloc-id
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# clean up
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# . *Next-alloc-id = 1
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c7 0/subop/copy 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 1/imm32 # copy to *Next-alloc-id
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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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lookup: # h : (handle T) -> eax : (addr T)
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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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# - as a proof of concept for future inlining, uses no general-purpose registers besides the output (eax)
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# eax = handle
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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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# - inline {
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# push handle->alloc_id
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ff 6/subop/push 0/mod/indirect 0/rm32/eax . . . . . . # push *eax
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# eax = handle->address (payload)
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8b/copy 1/mod/*+disp8 0/rm32/eax . . . . 4/disp8 . # copy *(eax+4) to eax
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# push handle->address
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50/push-eax
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# eax = payload->alloc_id
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8b/copy 0/mod/indirect 0/rm32/eax . . . . . . # copy *eax to eax
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# if (eax != handle->alloc_id) abort
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39/compare 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 0/r32/eax 4/disp8 . # compare *(esp+4) and eax
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75/jump-if-not-equal $lookup:abort/disp8
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# eax = pop handle->address
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58/pop-to-eax
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# discard handle->alloc_id
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
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# add 4
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05/add-to-eax 4/imm32
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# - }
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# - alternative consuming a second register {
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#? # ecx = handle->alloc_id
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#? 8b/copy 0/mod/indirect 0/rm32/eax . . . 1/r32/ecx . . # copy *eax to ecx
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#? # eax = handle->address (payload)
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#? 8b/copy 1/mod/*+disp8 0/rm32/eax . . . 0/r32/eax 4/disp8 . # copy *(eax+4) to eax
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#? # if (ecx != *eax) abort
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#? 39/compare 0/mod/indirect 0/rm32/eax . . . 1/r32/ecx . . # compare *eax and ecx
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#? 75/jump-if-not-equal $lookup:abort/disp8
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#? # add 4 to eax
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#? 05/add-to-eax 4/imm32
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# - }
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# . epilogue
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89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
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5d/pop-to-ebp
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c3/return
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$lookup:abort:
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# . _write(2/stderr, msg)
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# . . push args
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68/push "lookup failed\n"/imm32
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68/push 2/imm32/stderr
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# . . call
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e8/call _write/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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# . syscall(exit, 1)
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bb/copy-to-ebx 1/imm32/exit-status
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b8/copy-to-eax 1/imm32/exit
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cd/syscall 0x80/imm8
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test-lookup-success:
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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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# var heap/ebx : (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 3/rm32/ebx . . . 4/r32/esp . . # copy esp to ebx
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# heap = new-segment(512)
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# . . push args
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53/push-ebx
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68/push 0x200/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 handle/ecx : (ref handle)
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68/push 0/imm32/address
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68/push 0/imm32/alloc-id
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89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx
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# var old_top/edx = heap->curr
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8b/copy 0/mod/indirect 3/rm32/ebx . . . 2/r32/edx . . # copy *ebx to edx
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# new(heap, 2, handle)
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# . . push args
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51/push-ecx
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68/push 2/imm32/size
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53/push-ebx
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# . . call
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e8/call new/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# eax = lookup(handle)
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# . . push args
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51/push-ecx
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# . . call
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e8/call lookup/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
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# eax contains old top of heap, except skipping the alloc id in the payload
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# . check-ints-equal(eax, old_top+4, msg)
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# . . push args
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68/push "F - test-lookup-success"/imm32
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81 0/subop/add 3/mod/direct 2/rm32/edx . . . . . 4/imm32 # add to edx
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52/push-edx
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50/push-eax
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# clean up
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# . *Next-alloc-id = 1
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c7 0/subop/copy 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 1/imm32 # copy to *Next-alloc-id
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# write(2/stderr, "lookup succeeded\n")
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# . . push args
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68/push "lookup succeeded\n"/imm32
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68/push 2/imm32/stderr
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# . . call
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e8/call write/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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# . restore registers
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5a/pop-to-edx
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59/pop-to-ecx
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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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test-lookup-failure:
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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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# var heap/esi : (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 6/rm32/esi . . . 4/r32/esp . . # copy esp to esi
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# heap = new-segment(512)
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# . . push args
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56/push-esi
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68/push 0x200/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 h1/ecx : (ref handle)
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68/push 0/imm32/address
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68/push 0/imm32/alloc-id
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89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx
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# var old_top/ebx = heap->curr
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8b/copy 0/mod/indirect 6/rm32/esi . . . 3/r32/ebx . . # copy *esi to ebx
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# first allocation, to h1
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# . new(heap, 2, h1)
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# . . push args
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51/push-ecx
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68/push 2/imm32/size
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56/push-esi
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# . . call
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e8/call new/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# reset heap->curr to mimic reclamation
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89/copy 0/mod/indirect 6/rm32/esi . . . 3/r32/ebx . . # copy ebx to *esi
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# second allocation that returns the same address as the first
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# var h2/edx : (ref handle)
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68/push 0/imm32/address
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68/push 0/imm32/alloc-id
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89/copy 3/mod/direct 2/rm32/edx . . . 4/r32/esp . . # copy esp to edx
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# . new(heap, 2, h2)
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# . . push args
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52/push-edx
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68/push 2/imm32/size
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56/push-esi
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# . . call
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e8/call new/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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# check-ints-equal(h1->address, h2->address, msg)
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# . . push args
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68/push "F - test-lookup-failure"/imm32
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ff 6/subop/push 1/mod/*+disp8 2/rm32/ecx . . . . 4/disp8 . # push *(edx+4)
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ff 6/subop/push 1/mod/*+disp8 1/rm32/ecx . . . . 4/disp8 . # push *(ecx+4)
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|
# . . call
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|
e8/call check-ints-equal/disp32
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|
# . . discard args
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|
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
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|
# lookup(h1) should crash
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|
# . . push args
|
|
51/push-ecx
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|
# . . call
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|
e8/call lookup/disp32
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|
# should never get past this point
|
|
# . . discard args
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|
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
|
|
# clean up
|
|
# . *Next-alloc-id = 1
|
|
c7 0/subop/copy 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 1/imm32 # copy to *Next-alloc-id
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|
# . epilogue
|
|
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
|
|
5d/pop-to-ebp
|
|
c3/return
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|
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|
== data
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|
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|
# Monotonically increasing counter for calls to 'new'
|
|
Next-alloc-id: # int
|
|
1/imm32
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# . . vim:nowrap:textwidth=0
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