Teach GDB that wchar_t is a built-in type in C++ mode

GDB is currently not aware that wchar_t is a built-in type in C++
mode.  This is usually not a problem because the debug info describes
the type, so when you have a program loaded, you don't notice this.
However, if you try expressions involving wchar_t before a program is
loaded, gdb errors out:

 (gdb) p (wchar_t)-1
 No symbol table is loaded.  Use the "file" command.
 (gdb) p L"hello"
 No type named wchar_t.
 (gdb) ptype L"hello"
 No type named wchar_t.

This commit teaches gdb about the type.  After:

 (gdb) p (wchar_t)-1
 $1 = -1 L'\xffffffff'
 (gdb) p L"hello"
 $2 = L"hello"
 (gdb) ptype L"hello"
 type = wchar_t [6]

Unlike char16_t/char32_t, unfortunately, the underlying type of
wchar_t is implementation dependent, both size and signness.  So this
requires adding a couple new gdbarch hooks.

I grepped the GCC code base for WCHAR_TYPE and WCHAR_TYPE_SIZE, and it
seems to me that the majority of the ABIs have a 4-byte signed
wchar_t, so that's what I made the default for GDB too.  And then I
looked for which ports have a 16-bit and/or unsigned wchar_t, and made
GDB follow suit.

gdb/ChangeLog:
2017-04-12  Pedro Alves  <palves@redhat.com>

	PR gdb/21323
	* c-lang.c (cplus_primitive_types) <cplus_primitive_type_wchar_t>:
	New enum value.
	(cplus_language_arch_info): Register cplus_primitive_type_wchar_t.
	* gdbtypes.h (struct builtin_type) <builtin_wchar>: New field.
	* gdbtypes.c (gdbtypes_post_init): Create the "wchar_t" type.
	* gdbarch.sh (wchar_bit, wchar_signed): New per-arch values.
	* gdbarch.h, gdbarch.c: Regenerate.
	* aarch64-tdep.c (aarch64_gdbarch_init): Override
	gdbarch_wchar_bit and gdbarch_wchar_signed.
	* alpha-tdep.c (alpha_gdbarch_init): Likewise.
	* arm-tdep.c (arm_gdbarch_init): Likewise.
	* avr-tdep.c (avr_gdbarch_init): Likewise.
	* h8300-tdep.c (h8300_gdbarch_init): Likewise.
	* i386-nto-tdep.c (i386nto_init_abi): Likewise.
	* i386-tdep.c (i386_go32_init_abi): Likewise.
	* m32r-tdep.c (m32r_gdbarch_init): Likewise.
	* moxie-tdep.c (moxie_gdbarch_init): Likewise.
	* nds32-tdep.c (nds32_gdbarch_init): Likewise.
	* rs6000-aix-tdep.c (rs6000_aix_init_osabi): Likewise.
	* sh-tdep.c (sh_gdbarch_init): Likewise.
	* sparc-tdep.c (sparc32_gdbarch_init): Likewise.
	* sparc64-tdep.c (sparc64_init_abi): Likewise.
	* windows-tdep.c (windows_init_abi): Likewise.
	* xstormy16-tdep.c (xstormy16_gdbarch_init): Likewise.

gdb/testsuite/ChangeLog:
2017-04-12  Pedro Alves  <palves@redhat.com>

	PR gdb/21323
	* gdb.cp/wide_char_types.c: Include <wchar.h>.
	(wchar): New global.
	* gdb.cp/wide_char_types.exp (wide_char_types_program)
	(do_test_wide_char, wide_char_types_no_program, top level): Add
	wchar_t testing.

1 files changed, 48 insertions, 0 deletions

diff --git a/gdb/gdbarch.c b/gdb/gdbarch.c
index 319a890..5664325 100644
--- a/gdb/gdbarch.c
+++ b/gdb/gdbarch.c
@@ -184,6 +184,8 @@ struct gdbarch
   const struct floatformat ** double_format;
   int long_double_bit;
   const struct floatformat ** long_double_format;
+  int wchar_bit;
+  int wchar_signed;
   gdbarch_floatformat_for_type_ftype *floatformat_for_type;
   int ptr_bit;
   int addr_bit;
@@ -389,6 +391,8 @@ gdbarch_alloc (const struct gdbarch_info *info,
   gdbarch->float_bit = 4*TARGET_CHAR_BIT;
   gdbarch->double_bit = 8*TARGET_CHAR_BIT;
   gdbarch->long_double_bit = 8*TARGET_CHAR_BIT;
+  gdbarch->wchar_bit = 4*TARGET_CHAR_BIT;
+  gdbarch->wchar_signed = -1;
   gdbarch->floatformat_for_type = default_floatformat_for_type;
   gdbarch->ptr_bit = gdbarch->int_bit;
   gdbarch->char_signed = -1;
@@ -533,6 +537,9 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of long_double_bit, invalid_p == 0 */
   if (gdbarch->long_double_format == 0)
     gdbarch->long_double_format = floatformats_ieee_double;
+  /* Skip verify of wchar_bit, invalid_p == 0 */
+  if (gdbarch->wchar_signed == -1)
+    gdbarch->wchar_signed = 1;
   /* Skip verify of floatformat_for_type, invalid_p == 0 */
   /* Skip verify of ptr_bit, invalid_p == 0 */
   if (gdbarch->addr_bit == 0)
@@ -1457,6 +1464,12 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
                       "gdbarch_dump: vtable_function_descriptors = %s\n",
                       plongest (gdbarch->vtable_function_descriptors));
   fprintf_unfiltered (file,
+                      "gdbarch_dump: wchar_bit = %s\n",
+                      plongest (gdbarch->wchar_bit));
+  fprintf_unfiltered (file,
+                      "gdbarch_dump: wchar_signed = %s\n",
+                      plongest (gdbarch->wchar_signed));
+  fprintf_unfiltered (file,
                       "gdbarch_dump: gdbarch_write_pc_p() = %d\n",
                       gdbarch_write_pc_p (gdbarch));
   fprintf_unfiltered (file,
@@ -1757,6 +1770,41 @@ set_gdbarch_long_double_format (struct gdbarch *gdbarch,
   gdbarch->long_double_format = long_double_format;
 }
 
+int
+gdbarch_wchar_bit (struct gdbarch *gdbarch)
+{
+  gdb_assert (gdbarch != NULL);
+  /* Skip verify of wchar_bit, invalid_p == 0 */
+  if (gdbarch_debug >= 2)
+    fprintf_unfiltered (gdb_stdlog, "gdbarch_wchar_bit called\n");
+  return gdbarch->wchar_bit;
+}
+
+void
+set_gdbarch_wchar_bit (struct gdbarch *gdbarch,
+                       int wchar_bit)
+{
+  gdbarch->wchar_bit = wchar_bit;
+}
+
+int
+gdbarch_wchar_signed (struct gdbarch *gdbarch)
+{
+  gdb_assert (gdbarch != NULL);
+  /* Check variable changed from pre-default.  */
+  gdb_assert (gdbarch->wchar_signed != -1);
+  if (gdbarch_debug >= 2)
+    fprintf_unfiltered (gdb_stdlog, "gdbarch_wchar_signed called\n");
+  return gdbarch->wchar_signed;
+}
+
+void
+set_gdbarch_wchar_signed (struct gdbarch *gdbarch,
+                          int wchar_signed)
+{
+  gdbarch->wchar_signed = wchar_signed;
+}
+
 const struct floatformat **
 gdbarch_floatformat_for_type (struct gdbarch *gdbarch, const char *name, int length)
 {