diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 2120df6..9c0f6b6 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2017-09-28  Tom Tromey  <tom@tromey.com>
+
+	* Makefile.in (SUBDIR_UNITTESTS_SRCS): Add new file.
+	(SUBDIR_UNITTESTS_OBS): Add new file.
+	* unittests/string-vprintf-selftests.c: New file.
+	* common/common-utils.c (string_vprintf): New function.
+	* common/common-utils.h (string_vprintf): Declare.
+
 2017-09-28  Alexander Shaposhnikov <alexander.v.shaposhnikov@gmail.com> (tiny patch)
 
 	* dwarf2read.c (open_and_init_dwp_file): Protect against dwp_file
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 9004b35..ff86ce9 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -533,6 +533,7 @@ SUBDIR_UNITTESTS_SRCS = \
 	unittests/optional-selftests.c \
 	unittests/ptid-selftests.c \
 	unittests/scoped_restore-selftests.c \
+	unittests/string-vprintf-selftests.c \
 	unittests/xml-utils-selftests.c
 
 SUBDIR_UNITTESTS_OBS = \
@@ -543,6 +544,7 @@ SUBDIR_UNITTESTS_OBS = \
 	optional-selftests.o \
 	ptid-selftests.o \
 	scoped_restore-selftests.o \
+	string-vprintf-selftests.o \
 	xml-utils-selftests.o
 
 # Opcodes currently live in one of two places.  Either they are in the
diff --git a/gdb/common/common-utils.c b/gdb/common/common-utils.c
index 6b10d11..d8c546a 100644
--- a/gdb/common/common-utils.c
+++ b/gdb/common/common-utils.c
@@ -174,6 +174,27 @@ string_printf (const char* fmt, ...)
   return str;
 }
 
+/* See documentation in common-utils.h.  */
+
+std::string
+string_vprintf (const char* fmt, va_list args)
+{
+  va_list vp;
+  size_t size;
+
+  va_copy (vp, args);
+  size = vsnprintf (NULL, 0, fmt, vp);
+  va_end (vp);
+
+  std::string str (size, '\0');
+
+  /* C++11 and later guarantee std::string uses contiguous memory and
+     always includes the terminating '\0'.  */
+  vsprintf (&str[0], fmt, args);
+
+  return str;
+}
+
 char *
 savestring (const char *ptr, size_t len)
 {
diff --git a/gdb/common/common-utils.h b/gdb/common/common-utils.h
index 6475c28..19724f9 100644
--- a/gdb/common/common-utils.h
+++ b/gdb/common/common-utils.h
@@ -63,6 +63,10 @@ int xsnprintf (char *str, size_t size, const char *format, ...)
 std::string string_printf (const char* fmt, ...)
   ATTRIBUTE_PRINTF (1, 2);
 
+/* Like string_printf, but takes a va_list.  */
+std::string string_vprintf (const char* fmt, va_list args)
+  ATTRIBUTE_PRINTF (1, 0);
+
 /* Make a copy of the string at PTR with LEN characters
    (and add a null character at the end in the copy).
    Uses malloc to get the space.  Returns the address of the copy.  */
diff --git a/gdb/unittests/string-vprintf-selftests.c b/gdb/unittests/string-vprintf-selftests.c
new file mode 100644
index 0000000..b84d0a5
--- /dev/null
+++ b/gdb/unittests/string-vprintf-selftests.c
@@ -0,0 +1,57 @@
+/* Self tests for string_vprintf for GDB, the GNU debugger.
+
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "selftest.h"
+#include "common/common-utils.h"
+
+namespace selftests {
+namespace string_vprintf {
+
+std::string
+format (const char *fmt, ...)
+{
+  va_list vp;
+
+  va_start (vp, fmt);
+  std::string result = ::string_vprintf (fmt, vp);
+  va_end (vp);
+  return result;
+}
+
+void
+run_tests ()
+{
+  /* Basic smoke tests.  */
+  SELF_CHECK (format ("%s", "test") == "test");
+  SELF_CHECK (format ("%d", 23) == "23");
+  SELF_CHECK (format ("%s %d %s", "test", 23, "done")
+	      == "test 23 done");
+  SELF_CHECK (format ("nothing") == "nothing");
+}
+
+}
+}
+
+void
+_initialize_string_vprintf_selftests ()
+{
+  selftests::register_test ("string_vprintf",
+			    selftests::string_vprintf::run_tests);
+}
