diff --git a/elf/Makefile b/elf/Makefile
index 16c89b6d07..21eed715ee 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -1652,8 +1652,6 @@ $(objpfx)tst-nodelete-dlclose.out: $(objpfx)tst-nodelete-dlclose-dso.so \
 
 tst-env-setuid-ENV = MALLOC_CHECK_=2 MALLOC_MMAP_THRESHOLD_=4096 \
 		     LD_HWCAP_MASK=0x1
-tst-env-setuid-tunables-ENV = \
-	GLIBC_TUNABLES=glibc.malloc.check=2:glibc.malloc.mmap_threshold=4096
 
 $(objpfx)tst-debug1: $(libdl)
 $(objpfx)tst-debug1.out: $(objpfx)tst-debug1mod1.so
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index a2be9cde2f..f67a09605e 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -171,6 +171,7 @@ parse_tunables (char *tunestr, char *valstring)
     return;
 
   char *p = tunestr;
+  size_t off = 0;
 
   while (true)
     {
@@ -184,7 +185,11 @@ parse_tunables (char *tunestr, char *valstring)
       /* If we reach the end of the string before getting a valid name-value
 	 pair, bail out.  */
       if (p[len] == '\0')
-	return;
+	{
+	  if (__libc_enable_secure)
+	    tunestr[off] = '\0';
+	  return;
+	}
 
       /* We did not find a valid name-value pair before encountering the
 	 colon.  */
@@ -210,35 +215,28 @@ parse_tunables (char *tunestr, char *valstring)
 
 	  if (tunable_is_name (cur->name, name))
 	    {
-	      /* If we are in a secure context (AT_SECURE) then ignore the tunable
-		 unless it is explicitly marked as secure.  Tunable values take
-		 precedence over their envvar aliases.  */
+	      /* If we are in a secure context (AT_SECURE) then ignore the
+		 tunable unless it is explicitly marked as secure.  Tunable
+		 values take precedence over their envvar aliases.  We write
+		 the tunables that are not SXID_ERASE, back to TUNESTR, thus
+		 dropping all SXID_ERASE tunables and any invalid or
+		 unrecognized tunables.  */
 	      if (__libc_enable_secure)
 		{
-		  if (cur->security_level == TUNABLE_SECLEVEL_SXID_ERASE)
+		  if (cur->security_level != TUNABLE_SECLEVEL_SXID_ERASE)
 		    {
-		      if (p[len] == '\0')
-			{
-			  /* Last tunable in the valstring.  Null-terminate and
-			     return.  */
-			  *name = '\0';
-			  return;
-			}
-		      else
-			{
-			  /* Remove the current tunable from the string.  We do
-			     this by overwriting the string starting from NAME
-			     (which is where the current tunable begins) with
-			     the remainder of the string.  We then have P point
-			     to NAME so that we continue in the correct
-			     position in the valstring.  */
-			  char *q = &p[len + 1];
-			  p = name;
-			  while (*q != '\0')
-			    *name++ = *q++;
-			  name[0] = '\0';
-			  len = 0;
-			}
+		      if (off > 0)
+			tunestr[off++] = ':';
+
+		      const char *n = cur->name;
+
+		      while (*n != '\0')
+			tunestr[off++] = *n++;
+
+		      tunestr[off++] = '=';
+
+		      for (size_t j = 0; j < len; j++)
+			tunestr[off++] = value[j];
 		    }
 
 		  if (cur->security_level != TUNABLE_SECLEVEL_NONE)
@@ -251,9 +249,7 @@ parse_tunables (char *tunestr, char *valstring)
 	    }
 	}
 
-      if (p[len] == '\0')
-	return;
-      else
+      if (p[len] != '\0')
 	p += len + 1;
     }
 }
diff --git a/elf/tst-env-setuid-common.c b/elf/tst-env-setuid-common.c
new file mode 100644
index 0000000000..0145599e30
--- /dev/null
+++ b/elf/tst-env-setuid-common.c
@@ -0,0 +1,195 @@
+/* Common routines for the tst-env-setuid tests.
+
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <support/support.h>
+#include <support/test-driver.h>
+
+#define CHILD_STATUS 42
+
+/* Return a GID which is not our current GID, but is present in the
+   supplementary group list.  */
+static gid_t
+choose_gid (void)
+{
+  const int count = 64;
+  gid_t groups[count];
+  int ret = getgroups (count, groups);
+  if (ret < 0)
+    {
+      printf ("getgroups: %m\n");
+      exit (1);
+    }
+  gid_t current = getgid ();
+  for (int i = 0; i < ret; ++i)
+    {
+      if (groups[i] != current)
+	return groups[i];
+    }
+  return 0;
+}
+
+/* Spawn and execute a program and verify that it returns the CHILD_STATUS.  */
+static pid_t
+do_execve (char **args)
+{
+  pid_t kid = vfork ();
+
+  if (kid < 0)
+    {
+      printf ("vfork: %m\n");
+      return -1;
+    }
+
+  if (kid == 0)
+    {
+      /* Child process.  */
+      execve (args[0], args, environ);
+      _exit (-errno);
+    }
+
+  if (kid < 0)
+    return 1;
+
+  int status;
+
+  if (waitpid (kid, &status, 0) < 0)
+    {
+      printf ("waitpid: %m\n");
+      return 1;
+    }
+
+  if (WEXITSTATUS (status) == EXIT_UNSUPPORTED)
+    return EXIT_UNSUPPORTED;
+
+  if (!WIFEXITED (status) || WEXITSTATUS (status) != CHILD_STATUS)
+    {
+      printf ("Unexpected exit status %d from child process\n",
+	      WEXITSTATUS (status));
+      return 1;
+    }
+  return 0;
+}
+
+/* Copies the executable into a restricted directory, so that we can
+   safely make it SGID with the TARGET group ID.  Then runs the
+   executable.  */
+static int
+run_executable_sgid (gid_t target, char *argv1)
+{
+  char *dirname = xasprintf ("%s/tst-tunables-setuid.%jd",
+			     test_dir, (intmax_t) getpid ());
+  char *execname = xasprintf ("%s/bin", dirname);
+  int infd = -1;
+  int outfd = -1;
+  int ret = 0;
+  if (mkdir (dirname, 0700) < 0)
+    {
+      printf ("mkdir: %m\n");
+      goto err;
+    }
+  infd = open ("/proc/self/exe", O_RDONLY);
+  if (infd < 0)
+    {
+      printf ("open (/proc/self/exe): %m\n");
+      goto err;
+    }
+  outfd = open (execname, O_WRONLY | O_CREAT | O_EXCL, 0700);
+  if (outfd < 0)
+    {
+      printf ("open (%s): %m\n", execname);
+      goto err;
+    }
+  char buf[4096];
+  for (;;)
+    {
+      ssize_t rdcount = read (infd, buf, sizeof (buf));
+      if (rdcount < 0)
+	{
+	  printf ("read: %m\n");
+	  goto err;
+	}
+      if (rdcount == 0)
+	break;
+      char *p = buf;
+      char *end = buf + rdcount;
+      while (p != end)
+	{
+	  ssize_t wrcount = write (outfd, buf, end - p);
+	  if (wrcount == 0)
+	    errno = ENOSPC;
+	  if (wrcount <= 0)
+	    {
+	      printf ("write: %m\n");
+	      goto err;
+	    }
+	  p += wrcount;
+	}
+    }
+  if (fchown (outfd, getuid (), target) < 0)
+    {
+      printf ("fchown (%s): %m\n", execname);
+      goto err;
+    }
+  if (fchmod (outfd, 02750) < 0)
+    {
+      printf ("fchmod (%s): %m\n", execname);
+      goto err;
+    }
+  if (close (outfd) < 0)
+    {
+      printf ("close (outfd): %m\n");
+      goto err;
+    }
+  if (close (infd) < 0)
+    {
+      printf ("close (infd): %m\n");
+      goto err;
+    }
+
+  char *args[] = {execname, argv1, NULL};
+
+  ret = do_execve (args);
+
+err:
+  if (outfd >= 0)
+    close (outfd);
+  if (infd >= 0)
+    close (infd);
+  if (execname)
+    {
+      unlink (execname);
+      free (execname);
+    }
+  if (dirname)
+    {
+      rmdir (dirname);
+      free (dirname);
+    }
+  return ret;
+}
diff --git a/elf/tst-env-setuid-tunables.c b/elf/tst-env-setuid-tunables.c
index 50bef8683d..0363622026 100644
--- a/elf/tst-env-setuid-tunables.c
+++ b/elf/tst-env-setuid-tunables.c
@@ -25,35 +25,47 @@
 #include "config.h"
 #undef _LIBC
 
-#define test_parent test_parent_tunables
-#define test_child test_child_tunables
+#include "tst-env-setuid-common.c"
 
-static int test_child_tunables (void);
-static int test_parent_tunables (void);
-
-#include "tst-env-setuid.c"
-
-#define CHILD_VALSTRING_VALUE "glibc.malloc.mmap_threshold=4096"
-#define PARENT_VALSTRING_VALUE \
-  "glibc.malloc.check=2:glibc.malloc.mmap_threshold=4096"
+const char *teststrings[] =
+{
+  "glibc.malloc.check=2:glibc.malloc.mmap_threshold=4096",
+  "glibc.malloc.check=2:glibc.malloc.check=2:glibc.malloc.mmap_threshold=4096",
+  "glibc.malloc.check=2:glibc.malloc.mmap_threshold=4096:glibc.malloc.check=2",
+  "glibc.malloc.garbage=2:glibc.maoc.mmap_threshold=4096:glibc.malloc.check=2",
+  "glibc.malloc.check=4:glibc.malloc.garbage=2:glibc.maoc.mmap_threshold=4096",
+  ":glibc.malloc.garbage=2:glibc.malloc.check=1",
+  "glibc.malloc.check=1:glibc.malloc.check=2",
+};
+
+const char *resultstrings[] =
+{
+  "glibc.malloc.mmap_threshold=4096",
+  "glibc.malloc.mmap_threshold=4096",
+  "glibc.malloc.mmap_threshold=4096",
+  "",
+  "",
+  "",
+  "",
+};
 
 static int
-test_child_tunables (void)
+test_child (int off)
 {
   const char *val = getenv ("GLIBC_TUNABLES");
 
 #if HAVE_TUNABLES
-  if (val != NULL && strcmp (val, CHILD_VALSTRING_VALUE) == 0)
+  if (val != NULL && strcmp (val, resultstrings[off]) == 0)
     return 0;
 
   if (val != NULL)
-    printf ("Unexpected GLIBC_TUNABLES VALUE %s\n", val);
+    printf ("[%d] Unexpected GLIBC_TUNABLES VALUE %s\n", off, val);
 
   return 1;
 #else
   if (val != NULL)
     {
-      printf ("GLIBC_TUNABLES not cleared\n");
+      printf ("[%d] GLIBC_TUNABLES not cleared\n", off);
       return 1;
     }
   return 0;
@@ -61,15 +73,57 @@ test_child_tunables (void)
 }
 
 static int
-test_parent_tunables (void)
+do_test (int argc, char **argv)
 {
-  const char *val = getenv ("GLIBC_TUNABLES");
+  /* Setgid child process.  */
+  if (argc == 2)
+    {
+      if (getgid () == getegid ())
+	{
+	  /* This can happen if the file system is mounted nosuid.  */
+	  fprintf (stderr, "SGID failed: GID and EGID match (%jd)\n",
+		   (intmax_t) getgid ());
+	  exit (EXIT_UNSUPPORTED);
+	}
 
-  if (val != NULL && strcmp (val, PARENT_VALSTRING_VALUE) == 0)
-    return 0;
+      int ret = test_child (atoi (argv[1]));
 
-  if (val != NULL)
-    printf ("Unexpected GLIBC_TUNABLES VALUE %s\n", val);
+      if (ret != 0)
+	exit (1);
 
-  return 1;
+      exit (CHILD_STATUS);
+    }
+  else
+    {
+      int ret = 0;
+
+      /* Try running a setgid program.  */
+      gid_t target = choose_gid ();
+      if (target == 0)
+	{
+	  fprintf (stderr,
+		   "Could not find a suitable GID for user %jd, skipping test\n",
+		   (intmax_t) getuid ());
+	  exit (0);
+	}
+
+      /* Spawn tests.  */
+      for (int i = 0; i < sizeof (teststrings) / sizeof (char *); i++)
+	{
+	  char buf[8];
+
+	  printf ("Spawned test for %s (%d)\n", teststrings[i], i);
+	  snprintf (buf, sizeof (buf), "%d\n", i);
+	  if (setenv ("GLIBC_TUNABLES", teststrings[i], 1) != 0)
+	    exit (1);
+	  ret |= run_executable_sgid (target, buf);
+	}
+      return ret;
+    }
+
+  /* Something went wrong and our argv was corrupted.  */
+  _exit (1);
 }
+
+#define TEST_FUNCTION_ARGV do_test
+#include <support/test-driver.c>
diff --git a/elf/tst-env-setuid.c b/elf/tst-env-setuid.c
index 60ae0ca380..9414d5dfaa 100644
--- a/elf/tst-env-setuid.c
+++ b/elf/tst-env-setuid.c
@@ -19,185 +19,10 @@
    MALLOC_CHECK_ and MALLOC_MMAP_THRESHOLD_ but also retain
    MALLOC_MMAP_THRESHOLD_ in an unprivileged child.  */
 
-#include <errno.h>
-#include <fcntl.h>
-#include <stdlib.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <string.h>
-#include <sys/stat.h>
-#include <sys/wait.h>
-#include <unistd.h>
-
-#include <support/support.h>
-#include <support/test-driver.h>
+#include "tst-env-setuid-common.c"
 
 static char SETGID_CHILD[] = "setgid-child";
-#define CHILD_STATUS 42
-
-/* Return a GID which is not our current GID, but is present in the
-   supplementary group list.  */
-static gid_t
-choose_gid (void)
-{
-  const int count = 64;
-  gid_t groups[count];
-  int ret = getgroups (count, groups);
-  if (ret < 0)
-    {
-      printf ("getgroups: %m\n");
-      exit (1);
-    }
-  gid_t current = getgid ();
-  for (int i = 0; i < ret; ++i)
-    {
-      if (groups[i] != current)
-	return groups[i];
-    }
-  return 0;
-}
-
-/* Spawn and execute a program and verify that it returns the CHILD_STATUS.  */
-static pid_t
-do_execve (char **args)
-{
-  pid_t kid = vfork ();
-
-  if (kid < 0)
-    {
-      printf ("vfork: %m\n");
-      return -1;
-    }
-
-  if (kid == 0)
-    {
-      /* Child process.  */
-      execve (args[0], args, environ);
-      _exit (-errno);
-    }
-
-  if (kid < 0)
-    return 1;
-
-  int status;
-
-  if (waitpid (kid, &status, 0) < 0)
-    {
-      printf ("waitpid: %m\n");
-      return 1;
-    }
-
-  if (WEXITSTATUS (status) == EXIT_UNSUPPORTED)
-    return EXIT_UNSUPPORTED;
-
-  if (!WIFEXITED (status) || WEXITSTATUS (status) != CHILD_STATUS)
-    {
-      printf ("Unexpected exit status %d from child process\n",
-	      WEXITSTATUS (status));
-      return 1;
-    }
-  return 0;
-}
-
-/* Copies the executable into a restricted directory, so that we can
-   safely make it SGID with the TARGET group ID.  Then runs the
-   executable.  */
-static int
-run_executable_sgid (gid_t target)
-{
-  char *dirname = xasprintf ("%s/tst-tunables-setuid.%jd",
-			     test_dir, (intmax_t) getpid ());
-  char *execname = xasprintf ("%s/bin", dirname);
-  int infd = -1;
-  int outfd = -1;
-  int ret = 0;
-  if (mkdir (dirname, 0700) < 0)
-    {
-      printf ("mkdir: %m\n");
-      goto err;
-    }
-  infd = open ("/proc/self/exe", O_RDONLY);
-  if (infd < 0)
-    {
-      printf ("open (/proc/self/exe): %m\n");
-      goto err;
-    }
-  outfd = open (execname, O_WRONLY | O_CREAT | O_EXCL, 0700);
-  if (outfd < 0)
-    {
-      printf ("open (%s): %m\n", execname);
-      goto err;
-    }
-  char buf[4096];
-  for (;;)
-    {
-      ssize_t rdcount = read (infd, buf, sizeof (buf));
-      if (rdcount < 0)
-	{
-	  printf ("read: %m\n");
-	  goto err;
-	}
-      if (rdcount == 0)
-	break;
-      char *p = buf;
-      char *end = buf + rdcount;
-      while (p != end)
-	{
-	  ssize_t wrcount = write (outfd, buf, end - p);
-	  if (wrcount == 0)
-	    errno = ENOSPC;
-	  if (wrcount <= 0)
-	    {
-	      printf ("write: %m\n");
-	      goto err;
-	    }
-	  p += wrcount;
-	}
-    }
-  if (fchown (outfd, getuid (), target) < 0)
-    {
-      printf ("fchown (%s): %m\n", execname);
-      goto err;
-    }
-  if (fchmod (outfd, 02750) < 0)
-    {
-      printf ("fchmod (%s): %m\n", execname);
-      goto err;
-    }
-  if (close (outfd) < 0)
-    {
-      printf ("close (outfd): %m\n");
-      goto err;
-    }
-  if (close (infd) < 0)
-    {
-      printf ("close (infd): %m\n");
-      goto err;
-    }
-
-  char *args[] = {execname, SETGID_CHILD, NULL};
-
-  ret = do_execve (args);
-
-err:
-  if (outfd >= 0)
-    close (outfd);
-  if (infd >= 0)
-    close (infd);
-  if (execname)
-    {
-      unlink (execname);
-      free (execname);
-    }
-  if (dirname)
-    {
-      rmdir (dirname);
-      free (dirname);
-    }
-  return ret;
-}
 
-#ifndef test_child
 static int
 test_child (void)
 {
@@ -221,9 +46,7 @@ test_child (void)
 
   return 0;
 }
-#endif
 
-#ifndef test_parent
 static int
 test_parent (void)
 {
@@ -247,7 +70,6 @@ test_parent (void)
 
   return 0;
 }
-#endif
 
 static int
 do_test (int argc, char **argv)
@@ -285,7 +107,7 @@ do_test (int argc, char **argv)
 	  exit (0);
 	}
 
-      return run_executable_sgid (target);
+      return run_executable_sgid (target, SETGID_CHILD);
     }
 
   /* Something went wrong and our argv was corrupted.  */
