7842 - new directory organization

Baremetal is now the default build target and therefore has its sources
at the top-level. Baremetal programs build using the phase-2 Mu toolchain
that requires a Linux kernel. This phase-2 codebase which used to be at
the top-level is now under the linux/ directory. Finally, the phase-2 toolchain,
while self-hosting, has a way to bootstrap from a C implementation, which
is now stored in linux/bootstrap. The bootstrap C implementation uses some
literate programming tools that are now in linux/bootstrap/tools.

So the whole thing has gotten inverted. Each directory should build one
artifact and include the main sources (along with standard library). Tools
used for building it are relegated to sub-directories, even though those
tools are often useful in their own right, and have had lots of interesting
programs written using them.

A couple of things have gotten dropped in this process:
  - I had old ways to run on just a Linux kernel, or with a Soso kernel.
    No more.
  - I had some old tooling for running a single test at the cursor. I haven't
    used that lately. Maybe I'll bring it back one day.

The reorg isn't done yet. Still to do:
  - redo documentation everywhere. All the README files, all other markdown,
    particularly vocabulary.md.
  - clean up how-to-run comments at the start of programs everywhere
  - rethink what to do with the html/ directory. Do we even want to keep
    supporting it?

In spite of these shortcomings, all the scripts at the top-level, linux/
and linux/bootstrap are working. The names of the scripts also feel reasonable.
This is a good milestone to take stock at.

1 files changed, 74 insertions, 0 deletions

diff --git a/linux/106stream.subx b/linux/106stream.subx
new file mode 100644
index 00000000..84d0580b
--- /dev/null
+++ b/linux/106stream.subx
@@ -0,0 +1,74 @@
+# streams: data structure for operating on arrays in a stateful manner
+#
+# A stream looks like this:
+#   write: int  # index at which writes go
+#   read: int  # index that we've read until
+#   data: (array byte)  # prefixed by size as usual
+#
+# some primitives for operating on streams:
+#   - clear-stream (clears everything but the data size)
+#   - rewind-stream (resets read pointer)
+
+== 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
+
+clear-stream:  # f: (addr stream byte)
+    # . prologue
+    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   5/rm32/ebp    .           .                         0/r32/eax   8/disp8         .                 # copy *(ebp+8) to eax
+    # var count/ecx: int = f->size
+    8b/copy                         1/mod/*+disp8   0/rm32/eax    .           .             .           1/r32/ecx   8/disp8         .                 # copy *(eax+8) to ecx
+    # var max/ecx: (addr byte) = &f->data[f->size]
+    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
+    # f->write = 0
+    c7          0/subop/copy        0/mod/direct    0/rm32/eax    .           .             .           .           .               0/imm32           # copy to *eax
+    # f->read = 0
+    c7          0/subop/copy        1/mod/*+disp8   0/rm32/eax    .           .             .           .           4/disp8         0/imm32           # copy to *(eax+4)
+    # - clear all stream data
+    # - this isn't strictly necessary, and it can slow things down *a lot*, but better safe than sorry.
+    # var curr/eax: (addr byte) = f->data
+    81          0/subop/add         3/mod/direct    0/rm32/eax    .           .             .           .           .               0xc/imm32         # add to eax
+$clear-stream:loop:
+    # if (curr >= max) break
+    39/compare                      3/mod/direct    0/rm32/eax    .           .             .           1/r32/ecx   .               .                 # compare eax with ecx
+    73/jump-if-addr>=  $clear-stream:end/disp8
+    # *curr = 0
+    c6          0/subop/copy-byte   0/mod/direct    0/rm32/eax    .           .             .           .           .               0/imm8            # copy byte to *eax
+    # ++curr
+    40/increment-eax
+    eb/jump  $clear-stream:loop/disp8
+$clear-stream:end:
+    # . restore registers
+    59/pop-to-ecx
+    58/pop-to-eax
+    # . epilogue
+    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
+    5d/pop-to-ebp
+    c3/return
+
+rewind-stream:  # f: (addr stream byte)
+    # . prologue
+    55/push-ebp
+    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
+    # . save registers
+    50/push-eax
+    # eax = f
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .                         0/r32/eax   8/disp8         .                 # copy *(ebp+8) to eax
+    # f->read = 0
+    c7          0/subop/copy        1/mod/*+disp8   0/rm32/eax    .           .             .           .           4/disp8         0/imm32           # copy to *(eax+4)
+$rewind-stream:end:
+    # . restore registers
+    58/pop-to-eax
+    # . epilogue
+    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
+    5d/pop-to-ebp
+    c3/return
+
+# . . vim:nowrap:textwidth=0