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, 126 insertions, 0 deletions

diff --git a/linux/bootstrap/029syscalls.cc b/linux/bootstrap/029syscalls.cc
new file mode 100644
index 00000000..84a6af34
--- /dev/null
+++ b/linux/bootstrap/029syscalls.cc
@@ -0,0 +1,126 @@
+:(before "End Initialize Op Names")
+put_new(Name, "cd", "software interrupt (int)");
+
+:(before "End Single-Byte Opcodes")
+case 0xcd: {  // int imm8 (software interrupt)
+  trace(Callstack_depth+1, "run") << "syscall" << end();
+  uint8_t code = next();
+  if (code != 0x80) {
+    raise << "Unimplemented interrupt code " << HEXBYTE << code << '\n' << end();
+    raise << "  Only `int 80h` supported for now.\n" << end();
+    break;
+  }
+  process_int80();
+  break;
+}
+
+:(code)
+void process_int80() {
+  switch (Reg[EAX].u) {
+  case 1:
+    exit(/*exit code*/Reg[EBX].u);
+    break;
+  case 3:
+    trace(Callstack_depth+1, "run") << "read: " << Reg[EBX].u << ' ' << Reg[ECX].u << ' ' << Reg[EDX].u << end();
+    Reg[EAX].i = read(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u);
+    trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << "read: " << strerror(errno) << '\n' << end();
+    break;
+  case 4:
+    trace(Callstack_depth+1, "run") << "write: " << Reg[EBX].u << ' ' << Reg[ECX].u << ' ' << Reg[EDX].u << end();
+    trace(Callstack_depth+1, "run") << Reg[ECX].u << " => " << mem_addr_string(Reg[ECX].u, Reg[EDX].u) << end();
+    Reg[EAX].i = write(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u);
+    trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << "write: " << strerror(errno) << '\n' << end();
+    break;
+  case 5: {
+    check_flags(ECX);
+    check_mode(EDX);
+    trace(Callstack_depth+1, "run") << "open: " << Reg[EBX].u << ' ' << Reg[ECX].u << end();
+    trace(Callstack_depth+1, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
+    Reg[EAX].i = open(/*filename*/mem_addr_kernel_string(Reg[EBX].u), /*flags*/Reg[ECX].u, /*mode*/0640);
+    trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << "open: " << strerror(errno) << '\n' << end();
+    break;
+  }
+  case 6:
+    trace(Callstack_depth+1, "run") << "close: " << Reg[EBX].u << end();
+    Reg[EAX].i = close(/*file descriptor*/Reg[EBX].u);
+    trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << "close: " << strerror(errno) << '\n' << end();
+    break;
+  case 8:
+    check_mode(ECX);
+    trace(Callstack_depth+1, "run") << "creat: " << Reg[EBX].u << end();
+    trace(Callstack_depth+1, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
+    Reg[EAX].i = creat(/*filename*/mem_addr_kernel_string(Reg[EBX].u), /*mode*/0640);
+    trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << "creat: " << strerror(errno) << '\n' << end();
+    break;
+  case 10:
+    trace(Callstack_depth+1, "run") << "unlink: " << Reg[EBX].u << end();
+    trace(Callstack_depth+1, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
+    Reg[EAX].i = unlink(/*filename*/mem_addr_kernel_string(Reg[EBX].u));
+    trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << "unlink: " << strerror(errno) << '\n' << end();
+    break;
+  case 38:
+    trace(Callstack_depth+1, "run") << "rename: " << Reg[EBX].u << " -> " << Reg[ECX].u << end();
+    trace(Callstack_depth+1, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
+    trace(Callstack_depth+1, "run") << Reg[ECX].u << " => " << mem_addr_kernel_string(Reg[ECX].u) << end();
+    Reg[EAX].i = rename(/*old filename*/mem_addr_kernel_string(Reg[EBX].u), /*new filename*/mem_addr_kernel_string(Reg[ECX].u));
+    trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << "rename: " << strerror(errno) << '\n' << end();
+    break;
+  case 90:  // mmap: allocate memory outside existing segment allocations
+    trace(Callstack_depth+1, "run") << "mmap: allocate new segment" << end();
+    // Ignore most arguments for now: address hint, protection flags, sharing flags, fd, offset.
+    // We only support anonymous maps.
+    Reg[EAX].u = new_segment(/*length*/read_mem_u32(Reg[EBX].u+0x4));
+    trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].u << end();
+    break;
+  case 0xa2:  // nanosleep
+    cerr << "not sleeping\n";
+    break;
+  default:
+    raise << HEXWORD << EIP << ": unimplemented syscall " << Reg[EAX].u << '\n' << end();
+  }
+}
+
+// SubX is oblivious to file permissions, directories, symbolic links, terminals, and much else besides.
+// Also ignoring any concurrency considerations for now.
+void check_flags(int reg) {
+  uint32_t flags = Reg[reg].u;
+  if (flags != ((flags & O_RDONLY) | (flags & O_WRONLY))) {
+    cerr << HEXWORD << EIP << ": most POSIX flags to the open() syscall are not supported. Just O_RDONLY and O_WRONLY for now. Zero concurrent access support.\n";
+    exit(1);
+  }
+  if ((flags & O_RDONLY) && (flags & O_WRONLY)) {
+    cerr << HEXWORD << EIP << ": can't open a file for both reading and writing at once. See http://man7.org/linux/man-pages/man2/open.2.html.\n";
+    exit(1);
+  }
+}
+
+void check_mode(int reg) {
+  if (Reg[reg].u != 0600) {
+    cerr << HEXWORD << EIP << ": SubX is oblivious to file permissions; register " << reg << " must be 0x180.\n";
+    exit(1);
+  }
+}
+
+:(before "End Globals")
+// Very primitive/fixed/insecure mmap segments for now.
+uint32_t Segments_allocated_above = END_HEAP;
+:(code)
+// always allocate multiples of the segment size
+uint32_t new_segment(uint32_t length) {
+  assert(length > 0);
+  uint32_t result = (Segments_allocated_above - length) & 0xff000000;  // same number of zeroes as SEGMENT_ALIGNMENT
+  if (result <= START_HEAP) {
+    raise << "Allocated too many segments; the VM ran out of memory. "
+          << "Maybe SEGMENT_ALIGNMENT can be smaller?\n" << die();
+  }
+  Mem.push_back(vma(result, result+length));
+  Segments_allocated_above = result;
+  return result;
+}