From c164f4fb6be4dcdf452e4276127a2cfabc32c33f Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Sat, 29 Dec 2018 14:32:27 -0800 Subject: 4889 - playing with kinda-safe pointers --- subx/apps/handle | Bin 0 -> 7639 bytes subx/apps/handle.subx | 211 ++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 211 insertions(+) create mode 100644 subx/apps/handle create mode 100644 subx/apps/handle.subx (limited to 'subx') diff --git a/subx/apps/handle b/subx/apps/handle new file mode 100644 index 00000000..ea73b522 Binary files /dev/null and b/subx/apps/handle differ diff --git a/subx/apps/handle.subx b/subx/apps/handle.subx new file mode 100644 index 00000000..eda89945 --- /dev/null +++ b/subx/apps/handle.subx @@ -0,0 +1,211 @@ +# A sketch of Mu-style handles or kinda-safe pointers, that add a modicum of +# checking to dynamically allocated memory. +# +# This approach avoids using 'allocate' directly in favor of two primitives: +# - 'new', which allocates some space (the 'payload'), stores the address +# along with an opaque 'alloc id' in a 'handle', and prepends the same +# alloc id to the payload. +# - 'lookup', which checks that the alloc id at the start of a handle matches +# the alloc id at the start of the payload before returning the address. +# +# Layout of a handle: +# offset 0: alloc id +# offset 4: address + +== 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 + +# main: + e8/call run-tests/disp32 # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'. + # syscall(exit, Num-test-failures) + 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures to EBX + b8/copy-to-EAX 1/imm32/exit + cd/syscall 0x80/imm8 + +new: # ad : (address allocation-descriptor), n : int, out : (address handle) + # . prolog + 55/push-EBP + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # . save registers + 50/push-EAX + 51/push-ECX + 52/push-EDX + # ECX = n+4 + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 1/r32/ECX 0xc/disp8 . # copy *(EBP+12) to ECX + 81 0/subop/add 3/mod/direct 1/rm32/ECX . . . . . 4/imm32 # add to ECX + # EAX = allocate(ad, ECX) + # . . push args + 51/push-ECX + ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 8/disp8 . # push *(EBP+8) + # . . call + e8/call allocate/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP + # EDX = out + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 2/r32/EDX 0x10/disp8 . # copy *(EBP+16) to EDX + # out->address = EAX + 89/copy 1/mod/*+disp8 2/rm32/EDX . . . 0/r32/EAX 4/disp8 . # copy EAX to *(EDX+4) + # if (EAX == 0) out->alloc_id = 0, return + 81 7/subop/compare 3/mod/direct 0/rm32/EAX . . . . . 0/imm32 # compare EAX + 75/jump-if-not-equal $new:continue/disp8 + c7 0/subop/copy 0/mod/indirect 2/rm32/EDX . . . . . 0/imm32 # copy to *EDX + eb/jump $new:end/disp8 +$new:continue: + # otherwise: + # ECX = *Next-alloc-id + 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 1/r32/ECX Next-alloc-id/disp32 # copy *Next-alloc-id to ECX + # *EAX = *Next-alloc-id/ECX + 89/copy 0/mod/indirect 0/rm32/EAX . . . 1/r32/ECX . . # copy ECX to *EAX + # out->alloc_id = *Next-alloc-id + 89/copy 0/mod/indirect 2/rm32/EDX . . . 1/r32/ECX . . # copy ECX to *EDX + # increment *Next-alloc-id + ff 0/subop/increment 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 # increment *Next-alloc-id +$new:end: + # . restore registers + 5a/pop-to-EDX + 59/pop-to-ECX + 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 + +test-new: # - this test uses the bottom of the stack segment as scratch space + # . prolog + 55/push-EBP + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # *Next-alloc-id = 0x34 + c7 0/subop/copy 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 0x34/imm32 # copy to *Next-alloc-id + # var ad/EAX : (address allocation-descriptor) = {0x0b000000, 0x0b00000a} + 68/push 0x0b00000a/imm32/limit + 68/push 0x0b000000/imm32/curr + 89/copy 3/mod/direct 0/rm32/EAX . . . 4/r32/ESP . . # copy ESP to EAX + # var handle/ECX = {0, 0} + 68/push 0/imm32/address + 68/push 0/imm32/alloc-id + 89/copy 3/mod/direct 1/rm32/ECX . . . 4/r32/ESP . . # copy ESP to ECX + # new(ad, 2, handle/ECX) + # . . push args + 51/push-ECX + 68/push 2/imm32/size + 50/push-EAX + # . . call + e8/call new/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + # check-ints-equal(handle->alloc_id, 0x34, msg) + # . . push args + 68/push "F - test-new: alloc id of handle"/imm32 + 68/push 0x34/imm32 + ff 6/subop/push 0/mod/indirect 1/rm32/ECX . . . . . . # push *ECX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + # check-ints-equal(handle->address, 0x0b000000, msg) + # . . push args + 68/push "F - test-new: address of handle"/imm32 + 68/push 0x0b000000/imm32 + ff 6/subop/push 1/mod/*+disp8 1/rm32/ECX . . . . 4/disp8 . # push *(ECX+4) + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + # check-ints-equal(*handle->address, 0x34, msg) + # . . push args + 68/push "F - test-new: alloc id of payload"/imm32 + 68/push 0x34/imm32 + 8b/copy 1/mod/*+disp8 1/rm32/ECX . . . 2/r32/EDX 4/disp8 . # copy *(ECX+4) to EDX + ff 6/subop/push 0/mod/indirect 2/rm32/EDX . . . . . . # push *EDX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + # check-ints-equal(*Next-alloc-id, 0x35) + # . . push args + 68/push "F - test-new: next alloc id"/imm32 + 68/push 0x35/imm32 + ff 6/subop/push 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 # copy to *Next-alloc-id + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + # clean up + # . *Next-alloc-id = 1 + c7 0/subop/copy 0/mod/direct 0/rm32/EAX . . . . . 1/imm32 # copy to *EAX + # . epilog + 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP + 5d/pop-to-EBP + c3/return + +test-new-failure: + # . prolog + 55/push-EBP + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # . *Next-alloc-id = 0x34 + c7 0/subop/copy 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 0x34/imm32 # copy to *Next-alloc-id + # define an allocation-descriptor with no space left + # . var ad/EAX : (address allocation-descriptor) = {0x10, 0x10} + 68/push 0x10/imm32/limit + 68/push 0x10/imm32/curr + 89/copy 3/mod/direct 0/rm32/EAX . . . 4/r32/ESP . . # copy ESP to EAX + # . var handle/ECX = {random, random} + 68/push 1234/imm32/address + 68/push 5678/imm32/alloc-id + 89/copy 3/mod/direct 1/rm32/ECX . . . 4/r32/ESP . . # copy ESP to ECX + # try to allocate + # . new(ad, 2, handle/ECX) + # . . push args + 51/push-ECX + 68/push 2/imm32/size + 50/push-EAX + # . . call + e8/call new/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + # handle should be cleared + # . check-ints-equal(handle->alloc_id, 0, msg) + # . . push args + 68/push "F - test-new-failure: alloc id of handle"/imm32 + 68/push 0/imm32 + ff 6/subop/push 0/mod/indirect 1/rm32/ECX . . . . . . # push *ECX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + # . check-ints-equal(handle->address, 0, msg) + # . . push args + 68/push "F - test-new-failure: address of handle"/imm32 + 68/push 0/imm32 + ff 6/subop/push 1/mod/*+disp8 1/rm32/ECX . . . . 4/disp8 . # push *(ECX+4) + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + # Next-alloc-id should be unmodified + # . check-ints-equal(*Next-alloc-id, 0x34) + # . . push args + 68/push "F - test-new-failure: next alloc id"/imm32 + 68/push 0x34/imm32 + ff 6/subop/push 0/mod/indirect 5/rm32/.disp32 . . . Next-alloc-id/disp32 # copy to *Next-alloc-id + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + # clean up + # . *Next-alloc-id = 1 + c7 0/subop/copy 0/mod/direct 0/rm32/EAX . . . . . 1/imm32 # copy 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 + +# Monotonically increasing counter for calls to 'new' +Next-alloc-id: + 01 00 00 00 # 1 + +# . . vim:nowrap:textwidth=0 -- cgit 1.4.1-2-gfad0