Add xml_escape_text_append and use it

[This patch should go on top of "linux_qxfer_libraries_svr4: Use
 std::string", I should have sent them together as a series.]

I noticed that linux_qxfer_libraries_svr4 used xml_escape_text, which
returns an std::string.  That string is then copied into a larger
buffer.  It would be more efficient if we had a version of
xml_escape_text which appended to an existing string instead of
returning a new one.  This is what this patch does.

I manually verified that the output of linux_qxfer_libraries_svr4 didn't
change before/after the patch.

gdb/ChangeLog:

	* common/xml-utils.c (xml_escape_text): Move code to...
	(xml_escape_text_append): ... this new function.
	* common/xml-utils.h (xml_escape_text_append): New declaration.
	* unittests/xml-utils-selftests.c (test_xml_escape_text_append):
	New function.
	(_initialize_xml_utils): register test_xml_escape_text_append as
	a selftest.

gdb/gdbserver/ChangeLog:

	* linux-low.c (linux_qxfer_libraries_svr4): Use
	xml_escape_text_append.

2 files changed, 24 insertions, 12 deletions

diff --git a/gdb/common/xml-utils.c b/gdb/common/xml-utils.c
index aba1722..3e1c2bf 100644
--- a/gdb/common/xml-utils.c
+++ b/gdb/common/xml-utils.c
@@ -20,37 +20,44 @@
 #include "common-defs.h"
 #include "xml-utils.h"
 
-/* Return a string with special characters from TEXT replaced by entity
-   references.  */
+/* See xml-utils.h.  */
 
 std::string
 xml_escape_text (const char *text)
 {
   std::string result;
 
+  xml_escape_text_append (&result, text);
+
+  return result;
+}
+
+/* See xml-utils.h.  */
+
+void
+xml_escape_text_append (std::string *result, const char *text)
+{
   /* Expand the result.  */
   for (int i = 0; text[i] != '\0'; i++)
     switch (text[i])
       {
       case '\'':
-	result += "'";
+	*result += "'";
 	break;
       case '\"':
-	result += """;
+	*result += """;
 	break;
       case '&':
-	result += "&";
+	*result += "&";
 	break;
       case '<':
-	result += "&lt;";
+	*result += "&lt;";
 	break;
       case '>':
-	result += "&gt;";
+	*result += "&gt;";
 	break;
       default:
-	result += text[i];
+	*result += text[i];
 	break;
       }
-
-  return result;
 }
diff --git a/gdb/common/xml-utils.h b/gdb/common/xml-utils.h
index b874016..3427ab2 100644
--- a/gdb/common/xml-utils.h
+++ b/gdb/common/xml-utils.h
@@ -20,9 +20,14 @@
 #ifndef XML_UTILS_H
 #define XML_UTILS_H
 
-/* Return a malloc allocated string with special characters from TEXT
-   replaced by entity references.  */
+/* Return a string with special characters from TEXT replaced by entity
+   references.  */
 
 extern std::string xml_escape_text (const char *text);
 
+/* Append TEXT to RESULT, with special characters replaced by entity
+   references.  */
+
+extern void xml_escape_text_append (std::string *result, const char *text);
+
 #endif