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.

gdb/ChangeLog

@@ -1,3 +1,13 @@
+2018-03-08  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* 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.
+
 2018-03-07  Alan Hayward  <alan.hayward@arm.com>
 
 	* defs.h: Remove MAX_REGISTER_SIZE.

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;
 }

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

gdb/gdbserver/ChangeLog

@@ -1,3 +1,8 @@
+2018-03-08  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* linux-low.c (linux_qxfer_libraries_svr4): Use
+	xml_escape_text_append.
+
 2018-03-08  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* linux-low.c (linux_qxfer_libraries_svr4): Use std::string.

gdb/gdbserver/linux-low.c

@@ -7136,12 +7136,12 @@ linux_qxfer_libraries_svr4 (const char *annex, unsigned char *readbuf,
 		  header_done = 1;
 		}
 
-	      std::string name = xml_escape_text ((char *) libname);
-	      string_appendf (document,
-			      "<library name=\"%s\" lm=\"0x%lx\" "
+	      string_appendf (document, "<library name=\"");
+	      xml_escape_text_append (&document, (char *) libname);
+	      string_appendf (document, "\" lm=\"0x%lx\" "
 			      "l_addr=\"0x%lx\" l_ld=\"0x%lx\"/>",
-			      name.c_str (), (unsigned long) lm_addr,
-			      (unsigned long) l_addr, (unsigned long) l_ld);
+			      (unsigned long) lm_addr, (unsigned long) l_addr,
+			      (unsigned long) l_ld);
 	    }
 	}
 

gdb/unittests/xml-utils-selftests.c

@@ -33,6 +33,18 @@ static void test_xml_escape_text ()
   SELF_CHECK (actual_output == expected_output);
 }
 
+static void test_xml_escape_text_append ()
+{
+  /* Make sure that we do indeed append.  */
+  std::string actual_output = "foo<xml>";
+  const char *input = "<this isn't=\"xml\"> &";
+  const char *expected_output
+    = "foo<xml>&lt;this isn&apos;t=&quot;xml&quot;&gt; &amp;";
+  xml_escape_text_append (&actual_output, input);
+
+  SELF_CHECK (actual_output == expected_output);
+}
+
 }
 }
 
@@ -41,4 +53,6 @@ _initialize_xml_utils ()
 {
   selftests::register_test ("xml_escape_text",
 			    selftests::xml_utils::test_xml_escape_text);
+  selftests::register_test ("xml_escape_text_append",
+			    selftests::xml_utils::test_xml_escape_text_append);
 }