some hacky checks for common errors

They're not really baked into the regular compilation process; I have to
remember to run them if I see strange behavior.

linux/bootstrap/033check_operands.cc

@@ -145,6 +145,10 @@ void init_permitted_arguments() {
   put(Permitted_arguments, "99", 0x00);
   // return
   put(Permitted_arguments, "c3", 0x00);
+  // enable/disable interrupts
+  // not really part of SubX; just needed in low-level boot.subx
+  put(Permitted_arguments, "fa", 0x00);
+  put(Permitted_arguments, "fb", 0x00);
 
   //// Class B: just op and disp8
   //  imm32 imm8  disp32 |disp16  disp8 subop modrm

misc_checks

@@ -0,0 +1,22 @@
+#!/bin/sh
+# Hackily check for certain kinds of errors.
+#
+# We still rely exclusively on linux/bootstrap/bootstrap for some static
+# checks on bare SubX code that aren't implemented yet in the self-hosted
+# translator phases.
+#
+# However, boot.subx uses instructions that bootstrap doesn't recognize. So we
+# won't check it.
+
+set -e
+
+cat $* [0-9]*.mu                                      |linux/mu      > a.subx
+
+cat misc_checks.subx mu-init.subx [0-9]*.subx a.subx  |linux/braces  > a.braces
+cat a.braces                                          |linux/calls   > a.calls
+cat a.calls                                           |linux/sigils  > a.sigils
+
+CXXFLAGS=-g linux/bootstrap/bootstrap --debug translate a.sigils -o a.elf
+# Translation will never succeed,
+# but if we get to "missing reference to global" errors, they're expected and
+# we've gotten to the end of what bootstrap can check for us.

misc_checks.subx

@@ -0,0 +1,3 @@
+== code 0x00000000
+
+== data 0x80000000