Handle biased types

In Ada, the programmer can request that a range type with a non-zero
base be stored in the minimal number of bits required for the range.
This is done by biasing the values; so, for example, a range of -7..-4
may be stored as two bits with a bias of -7.

This patch implements this for gdb.  It is done by adding a bias to
struct range_bounds and then adjusting a few spots to handle this.

The test case is written to use -fgnat-encodings=minimal, but a future
compiler patch will change the compiler to emit DW_AT_GNU_bias with
-fgnat-encodings=gdb.  It seemed good to get the gdb patch in first.

Tested on x86-64 Fedora 29; plus a variety of targets using AdaCore's
internal test suite.

gdb/ChangeLog
2019-09-03  Tom Tromey  <tromey@adacore.com>

	* ada-valprint.c (ada_val_print_num): Don't recurse for range
	types.
	(has_negatives): Unbias a range type bound.
	* dwarf2read.c (read_subrange_type): Handle DW_AT_GNU_bias.
	* gdbtypes.c (operator==): Handle new field.
	(create_range_type): Add "bias" parameter.
	(create_static_range_type, resolve_dynamic_range): Update.
	* gdbtypes.h (struct range_bounds) <bias>: New member.
	(create_range_type): Add bias parameter.
	* printcmd.c (print_scalar_formatted): Unbias range types.
	* value.c (unpack_long): Unbias range types.
	(pack_long): Bias range types.

gdb/testsuite/ChangeLog
2019-09-03  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/bias.exp: New file.
	* gdb.ada/bias/bias.adb: New file.
	* gdb.ada/print_chars.exp: Add regression test.
	* gdb.ada/print_chars/foo.adb (My_Character): New type.
	(MC): New variable.

1 files changed, 13 insertions, 5 deletions

diff --git a/gdb/value.c b/gdb/value.c
index 9103d8f..d58a964 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -2751,10 +2751,16 @@ unpack_long (struct type *type, const gdb_byte *valaddr)
     case TYPE_CODE_CHAR:
     case TYPE_CODE_RANGE:
     case TYPE_CODE_MEMBERPTR:
-      if (nosign)
-	return extract_unsigned_integer (valaddr, len, byte_order);
-      else
-	return extract_signed_integer (valaddr, len, byte_order);
+      {
+	LONGEST result;
+	if (nosign)
+	  result = extract_unsigned_integer (valaddr, len, byte_order);
+	else
+	  result = extract_signed_integer (valaddr, len, byte_order);
+	if (code == TYPE_CODE_RANGE)
+	  result += TYPE_RANGE_DATA (type)->bias;
+	return result;
+      }
 
     case TYPE_CODE_FLT:
     case TYPE_CODE_DECFLOAT:
@@ -3315,12 +3321,14 @@ pack_long (gdb_byte *buf, struct type *type, LONGEST num)
 
   switch (TYPE_CODE (type))
     {
+    case TYPE_CODE_RANGE:
+      num -= TYPE_RANGE_DATA (type)->bias;
+      /* Fall through.  */
     case TYPE_CODE_INT:
     case TYPE_CODE_CHAR:
     case TYPE_CODE_ENUM:
     case TYPE_CODE_FLAGS:
     case TYPE_CODE_BOOL:
-    case TYPE_CODE_RANGE:
     case TYPE_CODE_MEMBERPTR:
       store_signed_integer (buf, len, byte_order, num);
       break;