Allow 'ptype/o' for assembly

PR exp/28359 points out that 'ptype/o' does not work when the current
language is "asm".

I tracked this down to a hard-coded list of languages in typeprint.c.
This patch replaces this list with a method on 'language_defn'
instead.  If all languages are ever updated to have this feature, the
method could be removed; but in the meantime this lets each language
control what happens.

I looked at having each print_type method simply modify the flags
itself, but this doesn't work very well with the feature that disables
method-printing by default (but allows it via a flag).

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28359
Approved-By: Andrew Burgess <aburgess@redhat.com>
Approved-By: Keith Seitz <keiths@redhat.com>

gdb/c-lang.c

@@ -816,6 +816,13 @@ public:
 
   /* See language.h.  */
 
+  bool can_print_type_offsets () const override
+  {
+    return true;
+  }
+
+  /* See language.h.  */
+
   void print_type (struct type *type, const char *varstring,
 		   struct ui_file *stream, int show, int level,
 		   const struct type_print_options *flags) const override
@@ -966,6 +973,13 @@ public:
 
   /* See language.h.  */
 
+  bool can_print_type_offsets () const override
+  {
+    return true;
+  }
+
+  /* See language.h.  */
+
   void print_type (struct type *type, const char *varstring,
 		   struct ui_file *stream, int show, int level,
 		   const struct type_print_options *flags) const override
@@ -1066,6 +1080,13 @@ public:
 
   /* See language.h.  */
 
+  bool can_print_type_offsets () const override
+  {
+    return true;
+  }
+
+  /* See language.h.  */
+
   void print_type (struct type *type, const char *varstring,
 		   struct ui_file *stream, int show, int level,
 		   const struct type_print_options *flags) const override
@@ -1118,6 +1139,13 @@ public:
 
   /* See language.h.  */
 
+  bool can_print_type_offsets () const override
+  {
+    return true;
+  }
+
+  /* See language.h.  */
+
   void print_type (struct type *type, const char *varstring,
 		   struct ui_file *stream, int show, int level,
 		   const struct type_print_options *flags) const override

gdb/d-lang.c

@@ -144,6 +144,13 @@ public:
 
   /* See language.h.  */
 
+  bool can_print_type_offsets () const override
+  {
+    return true;
+  }
+
+  /* See language.h.  */
+
   void print_type (struct type *type, const char *varstring,
 		   struct ui_file *stream, int show, int level,
 		   const struct type_print_options *flags) const override

gdb/language.h

@@ -451,6 +451,13 @@ struct language_defn
     return nullptr;
   }
 
+  /* Return true if this class' implementation of print_type can
+     handle the /o modifier.  */
+  virtual bool can_print_type_offsets () const
+  {
+    return false;
+  }
+
   /* Print TYPE to STREAM using syntax appropriate for this language.
      LEVEL is the depth to indent lines by.  VARSTRING, if not NULL or the
      empty string, is the name of a variable and TYPE should be printed in

gdb/objc-lang.c

@@ -266,6 +266,13 @@ public:
 
   /* See language.h.  */
 
+  bool can_print_type_offsets () const override
+  {
+    return true;
+  }
+
+  /* See language.h.  */
+
   void print_type (struct type *type, const char *varstring,
 		   struct ui_file *stream, int show, int level,
 		   const struct type_print_options *flags) const override

gdb/opencl-lang.c

@@ -953,6 +953,13 @@ public:
 
   /* See language.h.  */
 
+  bool can_print_type_offsets () const override
+  {
+    return true;
+  }
+
+  /* See language.h.  */
+
   void print_type (struct type *type, const char *varstring,
 		   struct ui_file *stream, int show, int level,
 		   const struct type_print_options *flags) const override

gdb/rust-lang.h

@@ -107,6 +107,13 @@ public:
 
   /* See language.h.  */
 
+  bool can_print_type_offsets () const override
+  {
+    return true;
+  }
+
+  /* See language.h.  */
+
   void print_type (struct type *type, const char *varstring,
 		   struct ui_file *stream, int show, int level,
 		   const struct type_print_options *flags) const override;

gdb/testsuite/gdb.base/ptype-offsets.exp

@@ -469,3 +469,16 @@ with_test_prefix "with_hex_default" {
   # restore
   gdb_test_no_output "set print type hex off"
 }
+
+gdb_test_no_output "set language asm"
+gdb_test "ptype/o struct tuv" \
+    [string_to_regexp [multi_line \
+  "/* offset      |    size */  type = struct tuv \{" \
+  "/*      0      |       4 */    int a1;" \
+  "/* XXX  4-byte hole      */" \
+  "/*      8      |       8 */    signed char *a2;" \
+  "/*     16      |       4 */    int a3;" \
+  "/* XXX  4-byte padding   */" \
+  "" \
+  "                               /* total size (bytes):   24 */" \
+  "                             \}"]]

gdb/typeprint.c

@@ -478,9 +478,7 @@ whatis_exp (const char *exp, int show)
 		    /* Filter out languages which don't implement the
 		       feature.  */
 		    if (show > 0
-			&& (current_language->la_language == language_c
+			&& current_language->can_print_type_offsets ())
-			    || current_language->la_language == language_cplus
-			    || current_language->la_language == language_rust))
 		      {
 			flags.print_offsets = 1;
 			flags.print_typedefs = 0;