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, 43 insertions, 0 deletions

diff --git a/linux/ex12.subx b/linux/ex12.subx
new file mode 100644
index 00000000..0c0d4315
--- /dev/null
+++ b/linux/ex12.subx
@@ -0,0 +1,43 @@
+# Example showing mmap syscall.
+# Create a new segment using mmap, save the address, write to it.
+#
+# To run:
+#   $ ./bootstrap translate init.linux apps/ex12.subx -o apps/ex12
+#   $ ./bootstrap run apps/ex12
+# You shouldn't get a segmentation fault.
+
+== 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:
+    # mmap(Mmap-new-segment->len)
+    bb/copy-to-ebx  Mmap-new-segment/imm32
+    e8/call  syscall_mmap/disp32
+
+    # write to *eax to check that we have access to the newly-allocated segment
+    c7          0/subop/copy        0/mod/direct    0/rm32/eax    .           .             .           .           .               0x34/imm32        # copy to *eax
+
+    # exit(eax)
+    89/copy                         3/mod/direct    3/rm32/ebx    .           .             .           0/r32/eax   .               .                 # copy eax to ebx
+    e8/call  syscall_exit/disp32
+
+== data
+
+# various constants used here were found in the Linux sources (search for file mman-common.h)
+Mmap-new-segment:  # type mmap_arg_struct
+    # addr
+    0/imm32
+    # len
+    0x100/imm32
+    # protection flags
+    3/imm32  # PROT_READ | PROT_WRITE
+    # sharing flags
+    0x22/imm32  # MAP_PRIVATE | MAP_ANONYMOUS
+    # fd
+    -1/imm32  # since MAP_ANONYMOUS is specified
+    # offset
+    0/imm32  # since MAP_ANONYMOUS is specified
+
+# . . vim:nowrap:textwidth=0