Make target_read_alloc & al return vectors

This patch started by changing target_read_alloc_1 to return a
byte_vector, to avoid manual memory management (in target_read_alloc_1
and in the callers).  To communicate failures to the callers, it
actually returns a gdb::optional<gdb::byte_vector>.

Adjusting target_read_stralloc was a bit more tricky, since it wants to
return a buffer of char, and not gdb_byte.  Since you can't just cast a
gdb::byte_vector into a gdb::def_vector<char>, I made
target_read_alloc_1 templated, so both versions (that return vectors of
gdb_byte and char) are generated.  Since target_read_stralloc now
returns a gdb::char_vector instead of a gdb::unique_xmalloc_ptr<char>, a
few callers need to be adjusted.

gdb/ChangeLog:

	* common/byte-vector.h (char_vector): New type.
	* target.h (target_read_alloc): Return
	gdb::optional<byte_vector>.
	(target_read_stralloc): Return gdb::optional<char_vector>.
	(target_get_osdata): Return gdb::optional<char_vector>.
	* target.c (target_read_alloc_1): Templatize.  Replacement
	manual memory management with vector.
	(target_read_alloc): Change return type, adjust.
	(target_read_stralloc): Change return type, adjust.
	(target_get_osdata): Change return type, adjust.
	* auxv.c (struct auxv_info) <length>: Remove.
	<data>: Change type to gdb::optional<byte_vector>.
	(auxv_inferior_data_cleanup): Free auxv_info with delete.
	(get_auxv_inferior_data): Allocate auxv_info with new, adjust.
	(target_auxv_search): Adjust.
	(fprint_target_auxv): Adjust.
	* avr-tdep.c (avr_io_reg_read_command): Adjust.
	* linux-tdep.c (linux_spu_make_corefile_notes): Adjust.
	(linux_make_corefile_notes): Adjust.
	* osdata.c (get_osdata): Adjust.
	* remote.c (remote_get_threads_with_qxfer): Adjust.
	(remote_memory_map): Adjust.
	(remote_traceframe_info): Adjust.
	(btrace_read_config): Adjust.
	(remote_read_btrace): Adjust.
	(remote_pid_to_exec_file): Adjust.
	* solib-aix.c (solib_aix_get_library_list): Adjust.
	* solib-dsbt.c (decode_loadmap): Don't free buf.
	(dsbt_get_initial_loadmaps): Adjust.
	* solib-svr4.c (svr4_current_sos_via_xfer_libraries): Adjust.
	* solib-target.c (solib_target_current_sos): Adjust.
	* tracepoint.c (sdata_make_value): Adjust.
	* xml-support.c (xinclude_start_include): Adjust.
	(xml_fetch_content_from_file): Adjust.
	* xml-support.h (xml_fetch_another): Change return type.
	(xml_fetch_content_from_file): Change return type.
	* xml-syscall.c (xml_init_syscalls_info): Adjust.
	* xml-tdesc.c (file_read_description_xml): Adjust.
	(fetch_available_features_from_target): Change return type.
	(target_fetch_description_xml): Adjust.
	(target_read_description_xml): Adjust.

gdb/linux-tdep.c

@@ -1420,47 +1420,41 @@ linux_spu_make_corefile_notes (bfd *obfd, char *note_data, int *note_size)
    };
 
   enum bfd_endian byte_order = gdbarch_byte_order (target_gdbarch ());
-  gdb_byte *spu_ids;
-  LONGEST i, j, size;
 
   /* Determine list of SPU ids.  */
-  size = target_read_alloc (&current_target, TARGET_OBJECT_SPU,
-			    NULL, &spu_ids);
+  gdb::optional<gdb::byte_vector>
+    spu_ids = target_read_alloc (&current_target, TARGET_OBJECT_SPU, NULL);
+
+  if (!spu_ids)
+    return nullptr;
 
   /* Generate corefile notes for each SPU file.  */
-  for (i = 0; i < size; i += 4)
+  for (size_t i = 0; i < spu_ids->size (); i += 4)
     {
-      int fd = extract_unsigned_integer (spu_ids + i, 4, byte_order);
+      int fd = extract_unsigned_integer (spu_ids->data () + i, 4, byte_order);
 
-      for (j = 0; j < sizeof (spu_files) / sizeof (spu_files[0]); j++)
+      for (size_t j = 0; j < sizeof (spu_files) / sizeof (spu_files[0]); j++)
 	{
 	  char annex[32], note_name[32];
-	  gdb_byte *spu_data;
-	  LONGEST spu_len;
 
 	  xsnprintf (annex, sizeof annex, "%d/%s", fd, spu_files[j]);
-	  spu_len = target_read_alloc (&current_target, TARGET_OBJECT_SPU,
-				       annex, &spu_data);
-	  if (spu_len > 0)
+	  gdb::optional<gdb::byte_vector> spu_data
+	    = target_read_alloc (&current_target, TARGET_OBJECT_SPU, annex);
+
+	  if (spu_data && !spu_data->empty ())
 	    {
 	      xsnprintf (note_name, sizeof note_name, "SPU/%s", annex);
 	      note_data = elfcore_write_note (obfd, note_data, note_size,
 					      note_name, NT_SPU,
-					      spu_data, spu_len);
-	      xfree (spu_data);
+					      spu_data->data (),
+					      spu_data->size ());
 
 	      if (!note_data)
-		{
-		  xfree (spu_ids);
-		  return NULL;
-		}
+		return nullptr;
 	    }
 	}
     }
 
-  if (size > 0)
-    xfree (spu_ids);
-
   return note_data;
 }
 
@@ -1911,8 +1905,6 @@ linux_make_corefile_notes (struct gdbarch *gdbarch, bfd *obfd, int *note_size)
   struct linux_corefile_thread_data thread_args;
   struct elf_internal_linux_prpsinfo prpsinfo;
   char *note_data = NULL;
-  gdb_byte *auxv;
-  int auxv_len;
   struct thread_info *curr_thr, *signalled_thr, *thr;
 
   if (! gdbarch_iterate_over_regset_sections_p (gdbarch))
@@ -1977,13 +1969,13 @@ linux_make_corefile_notes (struct gdbarch *gdbarch, bfd *obfd, int *note_size)
     return NULL;
 
   /* Auxillary vector.  */
-  auxv_len = target_read_alloc (&current_target, TARGET_OBJECT_AUXV,
-				NULL, &auxv);
-  if (auxv_len > 0)
+  gdb::optional<gdb::byte_vector> auxv =
+    target_read_alloc (&current_target, TARGET_OBJECT_AUXV, NULL);
+  if (auxv && !auxv->empty ())
     {
       note_data = elfcore_write_note (obfd, note_data, note_size,
-				      "CORE", NT_AUXV, auxv, auxv_len);
-      xfree (auxv);
+				      "CORE", NT_AUXV, auxv->data (),
+				      auxv->size ());
 
       if (!note_data)
 	return NULL;