as: add support for Sym1-Sym2 expressions

erlang/apps/as/src/assemble.erl

@@ -1,7 +1,7 @@
 %%% -*- erlang-indent-level: 2 -*-
 %%%
 %%% sections assembler for pdp10-elf as
-%%% Copyright (C) 2013-2020  Mikael Pettersson
+%%% Copyright (C) 2013-2023  Mikael Pettersson
 %%%
 %%% This file is part of pdp10-tools.
 %%%
@@ -183,16 +183,48 @@ exprs_values([Expr | Exprs], Tunit, SectionName, Dot, Size, Context, AccValues,
   {ok, {Value, Relocs}} = expr_value(Expr, Tunit, SectionName, Dot, Context),
   exprs_values(Exprs, Tunit, SectionName, Dot + Size, Size, Context, [Value | AccValues], Relocs ++ AccRelocs).
 
-expr_value(Expr, Tunit, SectionName, Dot, Context) ->
-  #expr{symbol = Name, offset = Offset, modifier = Modifier} = Expr,
-  case Name of
-    false -> make_abs(Context, Modifier, Offset);
-    "." -> make_rel(Context, Modifier, Dot, SectionName, Dot + Offset);
-    _ ->
-      case tunit:get_symbol(Tunit, Name) of
-        #symbol{section = abs, st_value = Value} when Value =/= false ->
-          make_abs(Context, Modifier, Value + Offset);
-        _ -> make_rel(Context, Modifier, Dot, Name, Offset)
+expr_value(Expr, Tunit, DotSection, Dot, Context) ->
+  #expr{modifier = Modifier} = Expr,
+  case expr_value(Expr, Tunit, DotSection, Dot) of
+    {Symbol, Offset} -> make_rel(Context, Modifier, Dot, Symbol, Offset);
+    Value -> make_abs(Context, Modifier, Value)
+  end.
+
+%% An expression can evaluate to:
+%% - Value when is_integer(Value)
+%% - {Symbol, Addend} when is_string(Symbol), is_integer(Addend)
+expr_value(Expr, Tunit, DotSection, Dot) ->
+  #expr{operand1 = Opnd1, operator = Op, operand2 = Opnd2} = Expr,
+  case {Op, operand_value(Opnd1, Tunit, DotSection, Dot), operand_value(Opnd2, Tunit, DotSection, Dot)} of
+    {'+', false, Value2} -> Value2;
+    {'+', {Sect1, Off1}, Value2} when is_integer(Value2) -> {Sect1, Off1 + Value2};
+    {'+', Value1, {Sect2, Off2}} when is_integer(Value1) -> {Sect2, Off2 + Value1};
+    {'+', Value1, Value2} when is_integer(Value1), is_integer(Value2) -> Value1 + Value2;
+    {'-', false, Value2} when is_integer(Value2) -> -Value2;
+    {'-', {Sect, Off1}, {Sect, Off2}} -> Off1 - Off2;
+    {'-', {Sect1, Off1}, Value2} when is_integer(Value2) -> {Sect1, Off1 - Value2};
+    {'-', Value1, Value2} when is_integer(Value1), is_integer(Value2) -> Value1 - Value2
+  end.
+
+%% An operand can evaluate to:
+%% - false
+%%   if the operand is absent
+%% - Value when is_integer(Value)
+%%   if the operand is an integer or an absolute symbol
+%% - {Section, Offset} when is_string(Section), is_integer(Offset)
+%%   if the operand is a label defined in the current translation unit
+%% - {Symbol, 0} when is_string(Symbol)
+%%   if the operand is an undefined symbol
+operand_value(Operand, Tunit, DotSection, Dot) ->
+  case Operand of
+    false -> false;
+    Value when is_integer(Value) -> Value;
+    "." -> {DotSection, Dot};
+    Symbol when is_list(Symbol) ->
+      case tunit:get_symbol(Tunit, Symbol) of
+        #symbol{section = abs, st_value = Value} when Value =/= false -> Value;
+        #symbol{section = Section, st_value = Value} when Value =/= false -> {Section, Value};
+        _ -> {Symbol, 0}
       end
   end.
 

erlang/apps/as/src/input.erl

@@ -1,7 +1,7 @@
 %%% -*- erlang-indent-level: 2 -*-
 %%%
 %%% input processing phase for pdp10-elf as
-%%% Copyright (C) 2013-2020  Mikael Pettersson
+%%% Copyright (C) 2013-2023  Mikael Pettersson
 %%%
 %%% This file is part of pdp10-tools.
 %%%
@@ -634,18 +634,19 @@ insn_fixup(Tunit, Insn) ->
   Insn#s_insn{address = expr_fixup(Tunit, Address)}.
 
 expr_fixup(Tunit, Expr) ->
-  case Expr of
-    #expr{symbol = {Number, Direction}} ->
-      LabelSerial = local_label_serial(Tunit, Number),
-      ReferenceSerial =
-        case Direction of
-          $b -> LabelSerial;
-          $f -> LabelSerial + 1
-        end,
-      Name = local_label_name(Number, ReferenceSerial),
-      Expr#expr{symbol = Name};
-    _ -> Expr
-  end.
+  #expr{operand1 = Operand1, operand2 = Operand2} = Expr,
+  Expr#expr{operand1 = operand_fixup(Tunit, Operand1),
+            operand2 = operand_fixup(Tunit, Operand2)}.
+
+operand_fixup(Tunit, {Number, Direction}) ->
+  LabelSerial = local_label_serial(Tunit, Number),
+  ReferenceSerial =
+    case Direction of
+      $b -> LabelSerial;
+      $f -> LabelSerial + 1
+    end,
+  local_label_name(Number, ReferenceSerial);
+operand_fixup(_Tunit, Operand) -> Operand.
 
 %% Initialization --------------------------------------------------------------
 

erlang/apps/as/src/parse.erl

@@ -1,7 +1,7 @@
 %%% -*- erlang-indent-level: 2 -*-
 %%%
 %%% parser for pdp10-elf as
-%%% Copyright (C) 2013-2020  Mikael Pettersson
+%%% Copyright (C) 2013-2023  Mikael Pettersson
 %%%
 %%% This file is part of pdp10-tools.
 %%%
@@ -605,8 +605,10 @@ section_name(ScanState) ->
 %%
 %% <plain_expr> ::= "(" <plain_expr> ")"
 %%                | "-"? <uinteger>
-%%                | (<symbol> | <local_label>) (("+" | "-") <uinteger>)?
+%%                | <symbol_or_label> (("+" | "-") <uinteger>)?
+%%                | <symbol_or_label> "-" <symbol_or_label>
 %%
+%% <symbol_or_label> := <symbol> | <local_label>
 %% <modifier> ::= "w" | "b" | "h"
 %%
 %% Note: <modifier> describes how the value should be represented, which also
@@ -709,6 +711,10 @@ do_expr_offset(ScanState, Symbol, IsMinus, Modifier) ->
   case scan:token(ScanState) of
     {ok, {_Location, {?T_UINTEGER, UInt}}} ->
       {ok, mk_symbol_expr(Symbol, if IsMinus -> -UInt; true -> UInt end, Modifier)};
+    {ok, {_Location, {?T_LOCAL_LABEL, Number, Direction}}} when IsMinus ->
+      {ok, mk_diff_expr(Symbol, _Symbol2 = {Number, Direction}, Modifier)};
+    {ok, {_Location, {?T_SYMBOL, Symbol2}}} when IsMinus ->
+      {ok, mk_diff_expr(Symbol, Symbol2, Modifier)};
     ScanRes -> badtok("expected <uinteger> after <sign>", ScanRes)
   end.
 
@@ -720,9 +726,10 @@ symbol_modifier(Symbol) ->
     _      -> error
   end.
 
-mk_integer_expr(Value, Modifier) -> #expr{symbol = false, offset = Value, modifier = Modifier}.
-mk_symbol_expr(Symbol, Modifier) -> #expr{symbol = Symbol, offset = 0, modifier = Modifier}.
-mk_symbol_expr(Symbol, Offset, Modifier) -> #expr{symbol = Symbol, offset = Offset, modifier = Modifier}.
+mk_integer_expr(Value, Modifier) -> #expr{operand1 = false, operator = '+', operand2 = Value, modifier = Modifier}.
+mk_symbol_expr(Symbol, Modifier) -> #expr{operand1 = false, operator = '+', operand2 = Symbol, modifier = Modifier}.
+mk_symbol_expr(Symbol, Offset, Modifier) -> #expr{operand1 = Symbol, operator = '+', operand2 = Offset, modifier = Modifier}.
+mk_diff_expr(Symbol1, Symbol2, Modifier) -> #expr{operand1 = Symbol1, operator = '-', operand2 = Symbol2, modifier = Modifier}.
 
 %% String Lists ----------------------------------------------------------------
 

erlang/apps/as/src/tunit.hrl

@@ -1,7 +1,7 @@
 %%% -*- erlang-indent-level: 2 -*-
 %%%
 %%% translation unit declarations for pdp10-elf as.
-%%% Copyright (C) 2013-2020  Mikael Pettersson
+%%% Copyright (C) 2013-2023  Mikael Pettersson
 %%%
 %%% This file is part of pdp10-tools.
 %%%
@@ -23,9 +23,13 @@
 
 %% An expression occurring in a statement. (TODO: extend)
 
+-type operand() :: string()                     % label or symbol, may be "."
+                 | {non_neg_integer(), $b | $f} % local label, eliminated before assembly
+                 | integer().
 -record(expr,
-        { symbol :: false | string() | {non_neg_integer(), $b | $f}
-        , offset :: integer()
+        { operand1 :: operand() | false
+        , operator :: '+' | '-'
+        , operand2 :: operand()
         , modifier :: false | w | b | h
         }).
 -type expr() :: #expr{}.