# write: like _write, but also support in-memory output streams (`ostream`s) # in addition to file descriptors. # # Our first dependency-injected and testable primitive. We can pass it either # a file descriptor or an address to an output stream or ostream. If a file # descriptor is passed in, we _write to it using the right syscall. If a 'fake # file descriptor' or ostream is passed in, we append to the output stream. # This lets us redirect output in tests and check it later. # # We assume our data segment will never begin at an address shorter than # 0x08000000, so any smaller arguments are assumed to be real file descriptors. # # An ostream looks like this: # write: int # index at which writes go # data: (array byte) # prefixed by length as usual == data # In-memory ostream for tests to write() to. # Also illustrates the layout of ostreams. Test-ostream: # current write 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 test-write-appends/disp32 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 write: # f : fd or (address stream), s : (address array byte) -> # 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 # if (f < 0x08000000) _write(f, s), return # f can't be a user-mode address, so treat it as a kernel file descriptor 81 7/subop/compare 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . . 8/disp8 0x08000000/imm32 # compare *(EBP+8) 7f/jump-if-greater $write:else/disp8 # push args ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . . 0xc/disp8 . # push *(EBP+12) ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . . 8/disp8 . # push *(EBP+8) # call e8/call _write/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP eb/jump $write:end/disp8 $write:else: # otherwise, treat 'f' as a stream to append to # # pseudocode: # destend = &f.data[t.length] # oldw = f.write # if s.length == 0 return # f.write += s.length # dest = &f.data[oldw] # srcend = &s.data[s.length] # src = &s.data[0] # while true: # if src >= srcend break # if dest >= destend break # for now silently ignore filled up ostream buffer # *dest = *src # ++src # ++dest # # 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) # f # EBX = *(EBP+12) # s # ECX = *(EAX+4) # f.length # ECX = EAX+8+ECX # destend = &f.data[f.length] # ESI = *EAX # oldw = f.write # EDX = *EBX # s.length # *EAX = *EAX + EDX # update f.write (allowed to go past f.length) # # do this here just because it's convenient # EAX = EAX+8+ESI # dest = &f.data[oldw] # ESI = EBX+4+EDX # srcend = &s.data[s.length] # EBX = EBX+4 # src = &s.data[0] # # EAX = f 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 = s 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none 3/r32/EBX 0xc/disp8 . # copy *(EBP+12) to EBX # ECX = f.length 8b/copy 1/mod/*+disp8 0/rm32/EAX . . . 1/r32/ECX 4/disp8 . # copy *(EAX+4) to ECX # ECX/destend = &f.data[f.length] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 0/base/EAX 1/index/ECX . 1/r32/ECX 8/disp8 . # copy EAX+ECX+8 to ECX # ESI/oldw = f.write 8b/copy 0/mod/indirect 0/rm32/EAX . . . 6/r32/ESI . . # copy *EAX to ESI # EDX = s.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 $write:end/disp8 # f.write += s.length 01/add 0/mod/indirect 0/rm32/EAX . . . 2/r32/EDX . . # add EDX to *EAX # EAX/dest = &f.data[oldw] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 0/base/EAX 6/index/ESI . 0/r32/EAX 8/disp8 . # copy EAX+ESI+8 to EAX # ESI/srcend = &s.data[s.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 = &s.data[0] 81 0/subop/add 3/mod/direct 3/rm32/EBX . . . . . 4/imm32 # add to EBX # while (true) $write: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 $write:end/disp8 # if EAX/dest >= ECX/destend break (for now silently ignore filled up ostream buffer) 39/compare 3/mod/direct 0/rm32/EAX . . . 1/r32/ECX . . # compare EAX with ECX 7d/jump-if-greater-or-equal $write:end/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 $write:loop/disp8 $write: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-ostream: # f : (address ostream) # 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 = f 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 = f.length 8b/copy 1/mod/*+disp8 0/rm32/EAX . . . 1/r32/ECX 4/disp8 . # copy *(EAX+4) to ECX # ECX = &f.data[f.length] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 0/base/EAX 1/index/ECX . 1/r32/ECX 8/disp8 . # copy EAX+ECX+8 to ECX # f.write = 0 c7/copy 0/mod/direct 0/rm32/EAX . . . . . 0/imm32 # copy to *EAX # EAX = f.data 81 0/subop/add 3/mod/direct 0/rm32/EAX . . . . . 8/imm32 # add to EAX # while (true) $clear-ostream: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-ostream: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-ostream:loop/disp8 $clear-ostream: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-write-single: # clear-ostream(Test-ostream) # push args 68/push Test-ostream/imm32 # call e8/call clear-ostream/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # write(Test-ostream, "Ab") # push args 68/push "Ab"/imm32 68/push Test-ostream/imm32 # call e8/call write/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # check-ints-equal(*Test-ostream.data, 41/A 62/b 00 00, msg) # push args 68/push "F - test-write-single"/imm32 68/push 0x006241/imm32/Ab # push *Test-ostream.data b8/copy-to-EAX Test-ostream/imm32 ff 6/subop/push 1/mod/*+disp8 0/rm32/EAX . . . . 8/disp8 . # push *(EAX+8) # 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-write-appends: # clear-ostream(Test-ostream) # push args 68/push Test-ostream/imm32 # call e8/call clear-ostream/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # write(Test-ostream, "C") # push args 68/push "C"/imm32 68/push Test-ostream/imm32 # call e8/call write/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # write(Test-ostream, "D") # push args 68/push "D"/imm32 68/push Test-ostream/imm32 # call e8/call write/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # check-ints-equal(*Test-ostream.data, 43/C 44/D 00 00, msg) # push args 68/push "F - test-write-appends"/imm32 68/push 0x00004443/imm32/C-D # push *Test-ostream.data b8/copy-to-EAX Test-ostream/imm32 ff 6/subop/push 1/mod/*+disp8 0/rm32/EAX . . . . 8/disp8 . # push *(EAX+8) # 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