about summary refs log tree commit diff stats
path: root/subx/056write.subx
diff options
context:
space:
mode:
Diffstat (limited to 'subx/056write.subx')
-rw-r--r--subx/056write.subx251
1 files changed, 251 insertions, 0 deletions
diff --git a/subx/056write.subx b/subx/056write.subx
new file mode 100644
index 00000000..46cc985b
--- /dev/null
+++ b/subx/056write.subx
@@ -0,0 +1,251 @@
+# 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) -> <void>
+  # 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  .           .           8/disp8         .                 # push *(EBP+8)
+  ff          6/subop/push        1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           .           0xc/disp8       .                 # push *(EBP+12)
+    # 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[f.write]
+  #   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  $write:end/disp8
+  # f.write += s.length
+  01/add                          0/mod/indirect  0/rm32/EAX    .           .             .           2/r32/EDX   .               .                 # add EDX to *EAX
+  # EAX/dest = &f.data[oldw]
+  8d/copy-address                 1/mod/*+disp8   4/rm32/sib    0/base/EAX  6/index/ESI   .           0/r32/EAX   8/disp8         .                 # copy EAX+ESI+8 to EAX
+  # ESI/srcend = &s.data[s.length]
+  8d/copy-address                 1/mod/*+disp8   4/rm32/sib    3/base/EBX  2/index/EDX   .           6/r32/ESI   4/disp8         .                 # copy EBX+EDX+4 to ESI
+  # EBX/src = &s.data
+  81          0/subop/add         3/mod/direct    3/rm32/EBX    .           .             .           .           .               4/imm32           # add to EBX
+  # while (true)
+$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