xml-support.c: Use std::string for growing string buffer

This main idea behind this patch is this change to xml-support.c:scope_level

  -  /* Body text accumulation.  This is an owning pointer.  */
  -  struct obstack *body;
  +  /* Body text accumulation.  */
  +  std::string body;

... which allows simplifying other parts of the code.

In target_fetch_description_xml, we want to distinguish between
returning "success + empty std::string" and "no success", and
gdb::optional is a natural fit for that.

gdb/ChangeLog:
2017-04-18  Pedro Alves  <palves@redhat.com>

	* tracefile-tfile.c (tfile_write_tdesc): Adjust to use
	gdb::optional<std::string>.
	* xml-support.c: Include <string>.
	(scope_level::scope_level(scope_level &&))
	(scope_level::~scope_level): Delete.
	(scope_level::body): Now a std::string.
	(gdb_xml_body_text, gdb_xml_end_element): Adjust.
	(xinclude_parsing_data::xinclude_parsing_data): Add 'output'
	parameter.
	(xinclude_parsing_data::~xinclude_parsing_data): Delete.
	(xinclude_parsing_data::output): Now a std::string reference.
	(xinclude_start_include): Adjust.
	(xml_xinclude_default): Adjust.
	(xml_process_xincludes): Add 'output' parameter, and return bool.
	* xml-support.h (xml_process_xincludes): Add 'output' parameter,
	and return bool.
	* xml-tdesc.c: Include <unordered_map> and <string>.
	(tdesc_xml_cache): Delete.
	(tdesc_xml_cache_s): Delete.
	(xml_cache): Now an std::unordered_map.
	(tdesc_parse_xml): Adjust to use std::string and unordered_map.
	(target_fetch_description_xml): Change return type to
	gdb::optional<std::string>, and adjust.
	* xml-tdesc.h: Include "common/gdb_optional.h" and <string>.
	(target_fetch_description_xml): Change return type to
	gdb::optional<std::string>.

1 files changed, 7 insertions, 7 deletions

diff --git a/gdb/tracefile-tfile.c b/gdb/tracefile-tfile.c
index 5d63c16..255bbc9 100644
--- a/gdb/tracefile-tfile.c
+++ b/gdb/tracefile-tfile.c
@@ -275,17 +275,19 @@ tfile_write_tdesc (struct trace_file_writer *self)
 {
   struct tfile_trace_file_writer *writer
     = (struct tfile_trace_file_writer *) self;
-  char *tdesc = target_fetch_description_xml (&current_target);
-  char *ptr = tdesc;
-  char *next;
 
-  if (tdesc == NULL)
+  gdb::optional<std::string> tdesc
+    = target_fetch_description_xml (&current_target);
+
+  if (!tdesc)
     return;
 
+  const char *ptr = tdesc->c_str ();
+
   /* Write tdesc line by line, prefixing each line with "tdesc ".  */
   while (ptr != NULL)
     {
-      next = strchr (ptr, '\n');
+      const char *next = strchr (ptr, '\n');
       if (next != NULL)
 	{
 	  fprintf (writer->fp, "tdesc %.*s\n", (int) (next - ptr), ptr);
@@ -299,8 +301,6 @@ tfile_write_tdesc (struct trace_file_writer *self)
 	}
       ptr = next;
     }
-
-  xfree (tdesc);
 }
 
 /* This is the implementation of trace_file_write_ops method