[gdb] Print user/includes fields for maint commands

The type struct compunit_symtab contains two fields (disregarding field next)
that express relations with other compunit_symtabs: user and includes.

These fields are currently not printed with "maint info symtabs" and
"maint print symbols".

Fix this such that for "maint info symtabs" we print:
...
   { ((struct compunit_symtab *) 0x23e8450)
     debugformat DWARF 2
     producer (null)
     dirname (null)
     blockvector ((struct blockvector *) 0x23e8590)
+    user ((struct compunit_symtab *) 0x2336280)
+    ( includes
+      ((struct compunit_symtab *) 0x23e85e0)
+      ((struct compunit_symtab *) 0x23e8960)
+    )
         { symtab <unknown> ((struct symtab *) 0x23e85b0)
           fullname (null)
           linetable ((struct linetable *) 0x0)
         }
   }
...

And for "maint print symbols" we print:
...
-Symtab for file <unknown>
+Symtab for file <unknown> at 0x23e85b0
 Read from object file /data/gdb_versions/devel/a.out (0x233ccf0)
 Language: c

 Blockvector:

 block #000, object at 0x23e8530, 0 syms/buckets in 0x0..0x0
   block #001, object at 0x23e84d0 under 0x23e8530, 0 syms/buckets in 0x0..0x0

+Compunit user: 0x2336300
+Compunit include: 0x23e8900
+Compunit include: 0x23dd970
...
Note: for user and includes we don't list the actual compunit_symtab address,
but instead the corresponding symtab address, which allows us to find that
symtab elsewhere in the output (given that we also now print the address of
symtabs).

gdb/ChangeLog:

2020-03-25  Tom de Vries  <tdevries@suse.de>

	* symtab.h (is_main_symtab_of_compunit_symtab): New function.
	* symmisc.c (dump_symtab_1): Print user and includes fields.
	(maintenance_info_symtabs): Same.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2020-03-25  Tom de Vries  <tdevries@suse.de>
+
+	* symtab.h (is_main_symtab_of_compunit_symtab): New function.
+	* symmisc.c (dump_symtab_1): Print user and includes fields.
+	(maintenance_info_symtabs): Same.
+
 2020-03-25  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	PR gdb/25534

gdb/symmisc.c

@@ -279,8 +279,10 @@ dump_symtab_1 (struct symtab *symtab, struct ui_file *outfile)
   const struct block *b;
   int depth;
 
-  fprintf_filtered (outfile, "\nSymtab for file %s\n",
-		    symtab_to_filename_for_display (symtab));
+  fprintf_filtered (outfile, "\nSymtab for file %s at %s\n",
+		    symtab_to_filename_for_display (symtab),
+		    host_address_to_string (symtab));
+
   if (SYMTAB_DIRNAME (symtab) != NULL)
     fprintf_filtered (outfile, "Compilation directory is %s\n",
 		      SYMTAB_DIRNAME (symtab));
@@ -308,7 +310,7 @@ dump_symtab_1 (struct symtab *symtab, struct ui_file *outfile)
     }
   /* Now print the block info, but only for compunit symtabs since we will
      print lots of duplicate info otherwise.  */
-  if (symtab == COMPUNIT_FILETABS (SYMTAB_COMPUNIT (symtab)))
+  if (is_main_symtab_of_compunit_symtab (symtab))
     {
       fprintf_filtered (outfile, "\nBlockvector:\n\n");
       bv = SYMTAB_BLOCKVECTOR (symtab);
@@ -371,6 +373,30 @@ dump_symtab_1 (struct symtab *symtab, struct ui_file *outfile)
 			"\nBlockvector same as owning compunit: %s\n\n",
 			compunit_filename);
     }
+
+  /* Print info about the user of this compunit_symtab, and the
+     compunit_symtabs included by this one. */
+  if (is_main_symtab_of_compunit_symtab (symtab))
+    {
+      struct compunit_symtab *cust = SYMTAB_COMPUNIT (symtab);
+
+      if (cust->user != nullptr)
+	{
+	  const char *addr
+	    = host_address_to_string (COMPUNIT_FILETABS (cust->user));
+	  fprintf_filtered (outfile, "Compunit user: %s\n", addr);
+	}
+      if (cust->includes != nullptr)
+	for (i = 0; ; ++i)
+	  {
+	    struct compunit_symtab *include = cust->includes[i];
+	    if (include == nullptr)
+	      break;
+	    const char *addr
+	      = host_address_to_string (COMPUNIT_FILETABS (include));
+	    fprintf_filtered (outfile, "Compunit include: %s\n", addr);
+	  }
+    }
 }
 
 static void
@@ -809,6 +835,28 @@ maintenance_info_symtabs (const char *regexp, int from_tty)
 					 " ((struct blockvector *) %s)\n",
 					 host_address_to_string
 				         (COMPUNIT_BLOCKVECTOR (cust)));
+			printf_filtered ("    user"
+					 " ((struct compunit_symtab *) %s)\n",
+					 cust->user != nullptr
+					 ? host_address_to_string (cust->user)
+					 : "(null)");
+			if (cust->includes != nullptr)
+			  {
+			    printf_filtered ("    ( includes\n");
+			    for (int i = 0; ; ++i)
+			      {
+				struct compunit_symtab *include
+				  = cust->includes[i];
+				if (include == nullptr)
+				  break;
+				const char *addr
+				  = host_address_to_string (include);
+				printf_filtered ("      (%s %s)\n",
+						 "(struct compunit_symtab *)",
+						 addr);
+			      }
+			    printf_filtered ("    )\n");
+			  }
 			printed_compunit_symtab_start = 1;
 		      }
 

gdb/symtab.h

@@ -1513,6 +1513,13 @@ extern struct symtab *
 
 extern enum language compunit_language (const struct compunit_symtab *cust);
 
+/* Return true if this symtab is the "main" symtab of its compunit_symtab.  */
+
+static inline bool
+is_main_symtab_of_compunit_symtab (struct symtab *symtab)
+{
+  return symtab == COMPUNIT_FILETABS (SYMTAB_COMPUNIT (symtab));
+}
 
 
 /* The virtual function table is now an array of structures which have the