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, 40 insertions, 0 deletions

diff --git a/linux/ex5.subx b/linux/ex5.subx
new file mode 100644
index 00000000..a2b0eeba
--- /dev/null
+++ b/linux/ex5.subx
@@ -0,0 +1,40 @@
+# Read a character from stdin, save it to a local on the stack, write it to stdout.
+#
+# To run:
+#   $ ./bootstrap translate init.linux apps/ex5.subx -o apps/ex5
+#   $ ./bootstrap run apps/ex5
+
+== 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
+
+Entry:
+
+    # allocate x on the stack
+    81          5/subop/subtract    3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # subtract from esp
+
+    # read(stdin, x, 1)
+    # . fd = 0 (stdin)
+    bb/copy-to-ebx  0/imm32
+    # . data = x (location to write result to)
+    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    4/base/esp  4/index/none              1/r32/ecx   4/disp8         .                 # copy esp+4 to ecx
+    # . size = 1 character
+    ba/copy-to-edx  1/imm32
+    # . syscall
+    e8/call  syscall_read/disp32
+
+    # syscall(write, stdout, x, 1)
+    # . fd = 1 (stdout)
+    bb/copy-to-ebx  1/imm32
+    # . data = x (location to read from)
+    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    4/base/esp  4/index/none              1/r32/ecx   4/disp8         .                 # copy esp+4 to ecx
+    # . size = 1 character
+    ba/copy-to-edx  1/imm32
+    # . syscall
+    e8/call  syscall_write/disp32
+
+    # exit(ebx)
+    e8/call  syscall_exit/disp32
+
+# . . vim:nowrap:textwidth=0