413 lines
22 KiB
Plaintext
413 lines
22 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 (from the subx directory):
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# $ ./subx translate *.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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# no Entry; the standard library runs all tests by default
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new: # ad : (address allocation-descriptor), n : int, out : (address handle)
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# . prolog
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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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# EAX = 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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# . epilog
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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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# . prolog
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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 : (address allocation-descriptor) = {0, 0}
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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 = {0, 0}
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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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# . epilog
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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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# . prolog
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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 : (address 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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# . epilog
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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 : (address T)
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# . prolog
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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 $lookup:abort/disp8
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#? # add 4 to EAX
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#? 05/add-to-EAX 4/imm32
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# - }
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# . epilog
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89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
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5d/pop-to-EBP
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c3/return
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$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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# . prolog
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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 : (address allocation-descriptor) = {0, 0}
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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 = {0, 0}
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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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# . epilog
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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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# . prolog
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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 : (address allocation-descriptor) = {0, 0}
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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 = {0, 0}
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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 = {0, 0}
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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
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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
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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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# 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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# . epilog
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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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# Monotonically increasing counter for calls to 'new'
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Next-alloc-id:
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1/imm32
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# . . vim:nowrap:textwidth=0
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