4535 - support for global variable names

1 files changed, 111 insertions, 0 deletions

diff --git a/subx/036global_variables.cc b/subx/036global_variables.cc
new file mode 100644
index 00000000..7a6463e0
--- /dev/null
+++ b/subx/036global_variables.cc
@@ -0,0 +1,111 @@
+//: Global variables.
+//:
+//: Global variables are just labels in the data segment.
+//: However, they can only be used in imm32 and not disp32 operands. And they
+//: can't be used with jump and call instructions.
+//:
+//: This layer much the same structure as rewriting labels.
+
+:(scenario global_variable)
+% Mem_offset = CODE_START;
+% Mem.resize(0x2000);
+== code
+b9/copy x/imm32  # copy to ECX
+== data
+x:
+00 00 00 00
++transform: global variable 'x' is at address 0x08049079
+
+:(before "End Level-2 Transforms")
+Transform.push_back(rewrite_global_variables);
+:(code)
+void rewrite_global_variables(program& p) {
+  trace(99, "transform") << "-- rewrite global variables" << end();
+  map<string, uint32_t> address;
+  compute_addresses_for_global_variables(p, address);
+  if (trace_contains_errors()) return;
+  drop_global_variables(p);
+  replace_global_variables_with_addresses(p, address);
+}
+
+void compute_addresses_for_global_variables(const program& p, map<string, uint32_t>& address) {
+  for (int i = /*skip code segment*/1;  i < SIZE(p.segments);  ++i)
+    compute_addresses_for_global_variables(p.segments.at(i), address);
+}
+
+void compute_addresses_for_global_variables(const segment& s, map<string, uint32_t>& address) {
+  int current_address = s.start;
+  for (int i = 0;  i < SIZE(s.lines);  ++i) {
+    const line& inst = s.lines.at(i);
+    for (int j = 0;  j < SIZE(inst.words);  ++j) {
+      const word& curr = inst.words.at(j);
+      if (*curr.data.rbegin() != ':') {
+        ++current_address;
+      }
+      else {
+        string variable = drop_last(curr.data);
+        // ensure variables look sufficiently different from raw hex
+        check_valid_name(variable);
+        if (trace_contains_errors()) return;
+        if (j > 0)
+          raise << "'" << to_string(inst) << "': global variable names can only be the first word in a line.\n" << end();
+        put(address, variable, current_address);
+        trace(99, "transform") << "global variable '" << variable << "' is at address 0x" << HEXWORD << current_address << end();
+        // no modifying current_address; global variable definitions won't be in the final binary
+      }
+    }
+  }
+}
+
+void drop_global_variables(program& p) {
+  for (int i = /*skip code segment*/1;  i < SIZE(p.segments);  ++i)
+    drop_labels(p.segments.at(i));
+}
+
+void replace_global_variables_with_addresses(program& p, const map<string, uint32_t>& address) {
+  if (p.segments.empty()) return;
+  segment& code = p.segments.at(0);
+  for (int i = 0;  i < SIZE(code.lines);  ++i) {
+    line& inst = code.lines.at(i);
+    line new_inst;
+    for (int j = 0;  j < SIZE(inst.words);  ++j) {
+      const word& curr = inst.words.at(j);
+      if (contains_key(address, curr.data)) {
+        uint32_t value = get(address, curr.data);
+        if (!has_metadata(curr, "imm32"))
+          raise << "'" << to_string(inst) << "': data variables should always be in '/imm32' operands\n" << end();
+        emit_hex_bytes(new_inst, value, 4);
+      }
+      else {
+        new_inst.words.push_back(curr);
+      }
+    }
+    inst.words.swap(new_inst.words);
+    trace(99, "transform") << "instruction after transform: '" << data_to_string(inst) << "'" << end();
+  }
+}
+
+:(scenario global_variable_disallowed_in_jump)
+% Mem_offset = CODE_START;
+% Hide_errors = true;
+== code
+eb/jump x/disp8
+== data
+x:
+00 00 00 00
++error: 'eb/jump x/disp8': data variables should always be in '/imm32' operands
+# sub-optimal error message; should be
+#? +error: can't jump to data (variable 'x')
+
+:(scenario global_variable_disallowed_in_call)
+% Mem_offset = CODE_START;
+% Hide_errors = true;
+== code
+e8/call x/disp32
+== data
+x:
+00 00 00 00
++error: 'e8/call x/disp32': data variables should always be in '/imm32' operands
+# sub-optimal error message; should be
+#? +error: can't call a data variable ('x')
+# also, what about function pointers?