# helpers for emitting traces to a trace stream, and for tests to check the trace stream # # A trace stream looks like this: # read : int # index that we've read until # write : int # index at which writes go # data : (array byte) # prefixed by length as usual # In a real trace the data will be in a special segment set aside for the purpose. # # primitives for operating on traces: # - initialize-trace-stream (update global variable) # - trace: stream, string # - die: stream (exit(1) if using real trace) # - check-trace-contains: stream, string/line, string/message (scans only from stream's read pointer, prints message to stderr on failure, updates stream's read pointer) # - rewind-reads: stream (resets read pointer) # - scan-to-next-line: stream (advance read pointer past next newline) # # Traces are very fundamental, so many of the helpers we create here won't be # used elsewhere; we'll switch to more bounds-checked variants. But here we get # bounds-checking for free; we allocate a completely disjoint segment for trace # data, and overflowing it will generate a page fault. == data # We'll save the address of the trace segment here. Trace-stream: 00 00 00 00 # Fake trace-stream for tests. # Also illustrates the layout of the real trace-stream (segment). Test-trace-stream: # current write index 00 00 00 00 # current read index 00 00 00 00 # length (= 8) 08 00 00 00 # data 00 00 00 00 00 00 00 00 # 8 bytes == code # instruction effective address operand 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: (manual test if this is the last file loaded) 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 . . 1/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures to EBX b8/copy-to-EAX 1/imm32 cd/syscall 0x80/imm8 # Allocate a new segment for the trace stream, initialize its length, and save its address to Trace-stream. # The Trace-stream segment will consist of variable-length lines separated by newlines (0x0a) initialize-trace-stream: # EAX = new-segment(0x1000) # push arg 68/push 0x1000/imm32/N # call e8/call new-segment/disp32 # discard arg 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # copy EAX to *Trace-stream 89/copy 0/mod/indirect 5/rm32/.disp32 . . 0/r32/EAX Trace-stream/disp32 # copy EAX to *Trace-stream # Trace-stream.length = 0x1000/N - 12 c7 0/copy 1/mod/*+disp8 0/rm32/EAX . . . . 8/disp8 0xff4/imm32 # copy 0xff4 to *(EAX+8) c3/return # Append to the given trace stream. trace: # t : (address trace-stream), line : string # 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 53/push-EBX 56/push-ESI # EAX = t 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none 0/r32/EAX 8/disp8 . # copy *(EBP+8) to EAX # EBX = line 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none 3/r32/EBX 0xc/disp8 . # copy *(EBP+12) to EBX # append line to t.data from t.write # # pseudocode: # destend = &t.data[t.length] # oldw = t.write # if line.length == 0 return # t.write += line.length + 1 # for newline # dest = &t.data[oldw] # srcend = &line.data[line.length] # src = &line.data[0] # while true: # if src >= srcend break # if dest >= destend break # for now silently ignore filled up trace buffer # *dest = *src # ++src # ++dest # if dest >= destend return # *dest = 10/newline # # key registers to set up for the loop: # EAX/dest, ECX/destend, EBX/src, ESI/srcend # we save EDX for byte operations (has to be one of the first 4 registers) # # register setup before the loop: # EAX = *(EBP+8) # t # EBX = *(EBP+12) # line # ECX = *(EAX+8) # t.length # ECX = EAX+12+ECX # destend = &t.data[t.length] # ESI = *EAX # oldw = t.write # EDX = *EBX # line.length # *EAX = *EAX + EDX # update t.write (allowed to go past t.length) # # do this here just because it's convenient # ++ *EAX # for the newline # EAX = EAX+12+ESI # dest = &t.data[t.write] # ESI = EBX+4+EDX # srcend = &line.data[line.length] # EBX = EBX+4 # src = &line.data[0] # # EAX/t and EBX/line are already initialized # ECX = t.length 8b/copy 1/mod/*+disp8 0/rm32/EAX . . . 1/r32/ECX 8/disp8 . # copy *(EAX+8) to ECX # ECX/destend = &t.data[t.length] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 0/base/EAX 1/index/ECX . 1/r32/ECX 0xc/disp8 . # copy EAX+ECX+12 to ECX # ESI/oldw = t.write 8b/copy 0/mod/indirect 0/rm32/EAX . . . 6/r32/ESI . . # copy *EAX to ESI # EDX = line.length 8b/copy 0/mod/indirect 3/rm32/EBX . . . 2/r32/EDX . . # copy *EBX to EDX # if EDX == 0 return 81 7/subop/compare 3/mod/direct 2/rm32/EDX . . . . . 0/imm32 # compare EDX 74/jump-if-equal $trace:end/disp8 # t.write += line.length 01/add 0/mod/indirect 0/rm32/EAX . . . 2/r32/EDX . . # add EDX to *EAX # t.write++ (for the newline we'll append below) 81 0/subop/add 0/mod/indirect 0/rm32/EAX . . . . . 1/imm32 # add to *EAX # EAX/dest = &t.data[oldw] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 0/base/EAX 6/index/ESI . 0/r32/EAX 0xc/disp8 . # copy EAX+ESI+12 to EAX # ESI/srcend = &line.data[line.length] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 3/base/EBX 2/index/EDX . 6/r32/ESI 4/disp8 . # copy EBX+EDX+4 to ESI # EBX/src = &line.data 81 0/subop/add 3/mod/direct 3/rm32/EBX . . . . . 4/imm32 # add to EBX # while (true) $trace:loop: # if EBX/src >= ESI/srcend break 39/compare 3/mod/direct 3/rm32/EBX . . . 6/r32/ESI . . # compare EBX with ESI 7d/jump-if-greater-or-equal $trace:break/disp8 # if EAX/dest >= ECX/destend break (for now silently ignore filled up trace buffer) 39/compare 3/mod/direct 0/rm32/EAX . . . 1/r32/ECX . . # compare EAX with ECX 7d/jump-if-greater-or-equal $trace:break/disp8 # copy one byte 8a/copy-byte 0/mod/indirect 3/rm32/EBX . . . 2/r32/DL . . # copy byte at *EBX to DL 88/copy-byte 0/mod/indirect 0/rm32/EAX . . . 2/r32/DL . . # copy byte at DL to *EAX # updates 40/increment-EAX 43/increment-EBX eb/jump $trace:loop/disp8 $trace:break: # finally, append a newline # if EAX/dest >= ECX/destend return 39/compare 3/mod/direct 0/rm32/EAX . . . 1/r32/ECX . . # compare EAX with ECX 7d/jump-if-greater-or-equal $trace:end/disp8 # append ba/copy-to-EDX 0x0a/imm32 88/copy-byte 0/mod/indirect 0/rm32/EAX . . . 2/r32/DL . . # copy byte at DL to *EAX $trace:end: # restore registers 5e/pop-to-ESI 5b/pop-to-EBX 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 clear-trace-stream: # t : (address trace-stream) # 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 # EAX = t 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none 0/r32/EAX 8/disp8 . # copy *(EBP+8) to EAX # ECX = t.length 8b/copy 1/mod/*+disp8 0/rm32/EAX . . . 1/r32/ECX 8/disp8 . # copy *(EAX+8) to ECX # ECX = &t.data[t.length] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 0/base/EAX 1/index/ECX . 1/r32/ECX 0xc/disp8 . # copy EAX+ECX+12 to ECX # t.write = 0 c7/copy 0/mod/direct 0/rm32/EAX . . . . . 0/imm32 # copy to *EAX # t.read = 0 c7/copy 1/mod/*+disp8 0/rm32/EAX . . . . 4/disp8 0/imm32 # copy to *(EAX+4) # EAX = t.data 81 0/subop/add 3/mod/direct 0/rm32/EAX . . . . . 0xc/imm32 # add to EAX # while (true) $clear-trace-stream:loop: # if EAX >= ECX break 39/compare 3/mod/direct 0/rm32/EAX . . . 1/r32/ECX . . # compare EAX with ECX 7d/jump-if-greater-or-equal $clear-trace-stream:end/disp8 # *EAX = 0 c7/copy 0/mod/direct 0/rm32/EAX . . . . . 0/imm32 # copy to *EAX # EAX += 4 81 0/subop/add 3/mod/direct 0/rm32/EAX . . . . . 4/imm32 # add to EAX eb/jump $clear-trace-stream:loop/disp8 $clear-trace-stream:end: # restore registers 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-trace-single: # clear-trace-stream(Test-trace-stream) # push args 68/push Test-trace-stream/imm32 # call e8/call clear-trace-stream/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # trace(Test-trace-stream, "Ab") # push args 68/push "Ab"/imm32 68/push Test-trace-stream/imm32 # call e8/call trace/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # check-ints-equal(*Test-trace-stream.data, 41/A 62/b 0a/newline 00, msg) # push args 68/push "F - test-trace-single"/imm32 68/push 0x0a6241/imm32/Ab-newline # push *Test-trace-stream.data b8/copy-to-EAX Test-trace-stream/imm32 ff 6/subop/push 1/mod/*+disp8 0/rm32/EAX . . . . 0xc/disp8 . # push *(EAX+12) # call e8/call check-ints-equal/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP # end c3/return test-trace-appends: # clear-trace-stream(Test-trace-stream) # push args 68/push Test-trace-stream/imm32 # call e8/call clear-trace-stream/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # trace(Test-trace-stream, "C") # push args 68/push "C"/imm32 68/push Test-trace-stream/imm32 # call e8/call trace/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # trace(Test-trace-stream, "D") # push args 68/push "D"/imm32 68/push Test-trace-stream/imm32 # call e8/call trace/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # check-ints-equal(*Test-trace-stream.data, 43/C 0a/newline 44/D 0a/newline, msg) # push args 68/push "F - test-trace-appends"/imm32 68/push 0x0a440a43/imm32/C-newline-D-newline # push *Test-trace-stream.data b8/copy-to-EAX Test-trace-stream/imm32 ff 6/subop/push 1/mod/*+disp8 0/rm32/EAX . . . . 0xc/disp8 . # push *(EAX+12) # call e8/call check-ints-equal/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP # end c3/return test-trace-empty-line: # clear-trace-stream(Test-trace-stream) # push args 68/push Test-trace-stream/imm32 # call e8/call clear-trace-stream/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # trace(Test-trace-stream, "") # push args 68/push ""/imm32 68/push Test-trace-stream/imm32 # call e8/call trace/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # check-ints-equal(*Test-trace-stream.data, 0, msg) # push args 68/push "F - test-trace-empty-line"/imm32 68/push 0/imm32 # push *Test-trace-stream.data b8/copy-to-EAX Test-trace-stream/imm32 ff 6/subop/push 1/mod/*+disp8 0/rm32/EAX . . . . 0xc/disp8 . # push *(EAX+12) # call e8/call check-ints-equal/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP # end c3/return # vim:nowrap:textwidth=0