This patch is a rework of the following upstream patch:

commit 1a4c27355e146b6d8cc6487b998462c7fdd1048f
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Thu Apr 11 18:12:00 2019 -0300

    elf: Fix pldd (BZ#18035)

    Since 9182aa67994 (Fix vDSO l_name for GDB's, BZ#387) the initial link_map
    for executable itself and loader will have both l_name and l_libname->name
    holding the same value due:

     elf/dl-object.c

     95   new->l_name = *realname ? realname : (char *) newname->name + libname_len - 1;

    Since newname->name points to new->l_libname->name.

    This leads to pldd to an infinite call at:

     elf/pldd-xx.c

    203     again:
    204       while (1)
    205         {
    206           ssize_t n = pread64 (memfd, tmpbuf.data, tmpbuf.length, name_offset);

    228           /* Try the l_libname element.  */
    229           struct E(libname_list) ln;
    230           if (pread64 (memfd, &ln, sizeof (ln), m.l_libname) == sizeof (ln))
    231             {
    232               name_offset = ln.name;
    233               goto again;
    234             }

    Since the value at ln.name (l_libname->name) will be the same as previously
    read. The straightforward fix is just avoid the check and read the new list
    entry.

    I checked also against binaries issues with old loaders with fix for BZ#387,
    and pldd could dump the shared objects.

    Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu, and
    powerpc64le-linux-gnu.

diff -Nrup a/elf/Makefile b/elf/Makefile
--- a/elf/Makefile	2019-05-17 12:35:12.663074766 -0400
+++ b/elf/Makefile	2019-05-17 12:35:45.816147975 -0400
@@ -201,6 +201,7 @@ tests-internal += loadtest unload unload
 	 neededtest neededtest2 neededtest3 neededtest4 \
 	 tst-tls3 tst-tls6 tst-tls7 tst-tls8 tst-dlmopen2 \
 	 tst-ptrguard1 tst-stackguard1 tst-libc_dlvsym
+tests-container += tst-pldd
 ifeq ($(build-hardcoded-path-in-tests),yes)
 tests += tst-dlopen-aout
 tst-dlopen-aout-no-pie = yes
diff -Nrup a/elf/pldd.c b/elf/pldd.c
--- a/elf/pldd.c	2018-08-01 01:10:47.000000000 -0400
+++ b/elf/pldd.c	2019-05-17 12:35:45.817147947 -0400
@@ -17,23 +17,17 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <alloca.h>
+#define _FILE_OFFSET_BITS 64
+
 #include <argp.h>
-#include <assert.h>
 #include <dirent.h>
-#include <elf.h>
-#include <errno.h>
 #include <error.h>
 #include <fcntl.h>
 #include <libintl.h>
-#include <link.h>
-#include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
 #include <unistd.h>
 #include <sys/ptrace.h>
-#include <sys/stat.h>
 #include <sys/wait.h>
 #include <scratch_buffer.h>
 
@@ -76,14 +70,8 @@ static struct argp argp =
   options, parse_opt, args_doc, doc, NULL, more_help, NULL
 };
 
-// File descriptor of /proc/*/mem file.
-static int memfd;
-
-/* Name of the executable  */
-static char *exe;
-
 /* Local functions.  */
-static int get_process_info (int dfd, long int pid);
+static int get_process_info (const char *exe, int dfd, long int pid);
 static void wait_for_ptrace_stop (long int pid);
 
 
@@ -102,8 +90,10 @@ main (int argc, char *argv[])
       return 1;
     }
 
-  assert (sizeof (pid_t) == sizeof (int)
-	  || sizeof (pid_t) == sizeof (long int));
+  _Static_assert (sizeof (pid_t) == sizeof (int)
+                 || sizeof (pid_t) == sizeof (long int),
+                 "sizeof (pid_t) != sizeof (int) or sizeof (long int)");
+
   char *endp;
   errno = 0;
   long int pid = strtol (argv[remaining], &endp, 10);
@@ -119,25 +109,24 @@ main (int argc, char *argv[])
   if (dfd == -1)
     error (EXIT_FAILURE, errno, gettext ("cannot open %s"), buf);
 
-  struct scratch_buffer exebuf;
-  scratch_buffer_init (&exebuf);
+  /* Name of the executable  */
+  struct scratch_buffer exe;
+  scratch_buffer_init (&exe);
   ssize_t nexe;
   while ((nexe = readlinkat (dfd, "exe",
-			     exebuf.data, exebuf.length)) == exebuf.length)
+                            exe.data, exe.length)) == exe.length)
     {
-      if (!scratch_buffer_grow (&exebuf))
+      if (!scratch_buffer_grow (&exe))
 	{
 	  nexe = -1;
 	  break;
 	}
     }
   if (nexe == -1)
-    exe = (char *) "<program name undetermined>";
+    /* Default stack allocation is at least 1024.  */
+    snprintf (exe.data, exe.length, "<program name undetermined>");
   else
-    {
-      exe = exebuf.data;
-      exe[nexe] = '\0';
-    }
+    ((char*)exe.data)[nexe] = '\0';
 
   /* Stop all threads since otherwise the list of loaded modules might
      change while we are reading it.  */
@@ -155,8 +144,8 @@ main (int argc, char *argv[])
     error (EXIT_FAILURE, errno, gettext ("cannot prepare reading %s/task"),
 	   buf);
 
-  struct dirent64 *d;
-  while ((d = readdir64 (dir)) != NULL)
+  struct dirent *d;
+  while ((d = readdir (dir)) != NULL)
     {
       if (! isdigit (d->d_name[0]))
 	continue;
@@ -182,7 +171,7 @@ main (int argc, char *argv[])
 
       wait_for_ptrace_stop (tid);
 
-      struct thread_list *newp = alloca (sizeof (*newp));
+      struct thread_list *newp = xmalloc (sizeof (*newp));
       newp->tid = tid;
       newp->next = thread_list;
       thread_list = newp;
@@ -190,17 +179,22 @@ main (int argc, char *argv[])
 
   closedir (dir);
 
-  int status = get_process_info (dfd, pid);
+  if (thread_list == NULL)
+    error (EXIT_FAILURE, 0, gettext ("no valid %s/task entries"), buf);
+
+  int status = get_process_info (exe.data, dfd, pid);
 
-  assert (thread_list != NULL);
   do
     {
       ptrace (PTRACE_DETACH, thread_list->tid, NULL, NULL);
+      struct thread_list *prev = thread_list;
       thread_list = thread_list->next;
+      free (prev);
     }
   while (thread_list != NULL);
 
   close (dfd);
+  scratch_buffer_free (&exe);
 
   return status;
 }
@@ -281,9 +275,10 @@ warranty; not even for MERCHANTABILITY o
 
 
 static int
-get_process_info (int dfd, long int pid)
+get_process_info (const char *exe, int dfd, long int pid)
 {
-  memfd = openat (dfd, "mem", O_RDONLY);
+  /* File descriptor of /proc/<pid>/mem file.  */
+  int memfd = openat (dfd, "mem", O_RDONLY);
   if (memfd == -1)
     goto no_info;
 
@@ -333,9 +328,9 @@ get_process_info (int dfd, long int pid)
 
   int retval;
   if (e_ident[EI_CLASS] == ELFCLASS32)
-    retval = find_maps32 (pid, auxv, auxv_size);
+    retval = find_maps32 (exe, memfd, pid, auxv, auxv_size);
   else
-    retval = find_maps64 (pid, auxv, auxv_size);
+    retval = find_maps64 (exe, memfd, pid, auxv, auxv_size);
 
   free (auxv);
   close (memfd);
diff -Nrup a/elf/pldd-xx.c b/elf/pldd-xx.c
--- a/elf/pldd-xx.c	2018-08-01 01:10:47.000000000 -0400
+++ b/elf/pldd-xx.c	2019-05-17 13:05:29.587147445 -0400
@@ -23,10 +23,6 @@
 #define EW_(e, w, t) EW__(e, w, _##t)
 #define EW__(e, w, t) e##w##t
 
-#define pldd_assert(name, exp) \
-  typedef int __assert_##name[((exp) != 0) - 1]
-
-
 struct E(link_map)
 {
   EW(Addr) l_addr;
@@ -39,12 +35,12 @@ struct E(link_map)
   EW(Addr) l_libname;
 };
 #if CLASS == __ELF_NATIVE_CLASS
-pldd_assert (l_addr, (offsetof (struct link_map, l_addr)
-			== offsetof (struct E(link_map), l_addr)));
-pldd_assert (l_name, (offsetof (struct link_map, l_name)
-			== offsetof (struct E(link_map), l_name)));
-pldd_assert (l_next, (offsetof (struct link_map, l_next)
-			== offsetof (struct E(link_map), l_next)));
+_Static_assert (offsetof (struct link_map, l_addr)
+               == offsetof (struct E(link_map), l_addr), "l_addr");
+_Static_assert (offsetof (struct link_map, l_name)
+               == offsetof (struct E(link_map), l_name), "l_name");
+_Static_assert (offsetof (struct link_map, l_next)
+               == offsetof (struct E(link_map), l_next), "l_next");
 #endif
 
 
@@ -54,10 +50,10 @@ struct E(libname_list)
   EW(Addr) next;
 };
 #if CLASS == __ELF_NATIVE_CLASS
-pldd_assert (name, (offsetof (struct libname_list, name)
-		      == offsetof (struct E(libname_list), name)));
-pldd_assert (next, (offsetof (struct libname_list, next)
-		      == offsetof (struct E(libname_list), next)));
+_Static_assert (offsetof (struct libname_list, name)
+               == offsetof (struct E(libname_list), name), "name");
+_Static_assert (offsetof (struct libname_list, next)
+               == offsetof (struct E(libname_list), next), "next");
 #endif
 
 struct E(r_debug)
@@ -69,16 +65,17 @@ struct E(r_debug)
   EW(Addr) r_map;
 };
 #if CLASS == __ELF_NATIVE_CLASS
-pldd_assert (r_version, (offsetof (struct r_debug, r_version)
-			   == offsetof (struct E(r_debug), r_version)));
-pldd_assert (r_map, (offsetof (struct r_debug, r_map)
-		       == offsetof (struct E(r_debug), r_map)));
+_Static_assert (offsetof (struct r_debug, r_version)
+               == offsetof (struct E(r_debug), r_version), "r_version");
+_Static_assert (offsetof (struct r_debug, r_map)
+               == offsetof (struct E(r_debug), r_map), "r_map");
 #endif
 
 
 static int
 
-E(find_maps) (pid_t pid, void *auxv, size_t auxv_size)
+E(find_maps) (const char *exe, int memfd, pid_t pid, void *auxv,
+             size_t auxv_size)
 {
   EW(Addr) phdr = 0;
   unsigned int phnum = 0;
@@ -104,12 +101,9 @@ E(find_maps) (pid_t pid, void *auxv, siz
   if (phdr == 0 || phnum == 0 || phent == 0)
     error (EXIT_FAILURE, 0, gettext ("cannot find program header of process"));
 
-  EW(Phdr) *p = alloca (phnum * phent);
-  if (pread64 (memfd, p, phnum * phent, phdr) != phnum * phent)
-    {
-      error (0, 0, gettext ("cannot read program header"));
-      return EXIT_FAILURE;
-    }
+  EW(Phdr) *p = xmalloc (phnum * phent);
+  if (pread (memfd, p, phnum * phent, phdr) != phnum * phent)
+    error (EXIT_FAILURE, 0, gettext ("cannot read program header"));
 
   /* Determine the load offset.  We need this for interpreting the
      other program header entries so we do this in a separate loop.
@@ -129,24 +123,18 @@ E(find_maps) (pid_t pid, void *auxv, siz
     if (p[i].p_type == PT_DYNAMIC)
       {
 	EW(Dyn) *dyn = xmalloc (p[i].p_filesz);
-	if (pread64 (memfd, dyn, p[i].p_filesz, offset + p[i].p_vaddr)
+       if (pread (memfd, dyn, p[i].p_filesz, offset + p[i].p_vaddr)
 	    != p[i].p_filesz)
-	  {
-	    error (0, 0, gettext ("cannot read dynamic section"));
-	    return EXIT_FAILURE;
-	  }
+         error (EXIT_FAILURE, 0, gettext ("cannot read dynamic section"));
 
 	/* Search for the DT_DEBUG entry.  */
 	for (unsigned int j = 0; j < p[i].p_filesz / sizeof (EW(Dyn)); ++j)
 	  if (dyn[j].d_tag == DT_DEBUG && dyn[j].d_un.d_ptr != 0)
 	    {
 	      struct E(r_debug) r;
-	      if (pread64 (memfd, &r, sizeof (r), dyn[j].d_un.d_ptr)
+             if (pread (memfd, &r, sizeof (r), dyn[j].d_un.d_ptr)
 		  != sizeof (r))
-		{
-		  error (0, 0, gettext ("cannot read r_debug"));
-		  return EXIT_FAILURE;
-		}
+               error (EXIT_FAILURE, 0, gettext ("cannot read r_debug"));
 
 	      if (r.r_map != 0)
 		{
@@ -160,13 +148,10 @@ E(find_maps) (pid_t pid, void *auxv, siz
       }
     else if (p[i].p_type == PT_INTERP)
       {
-	interp = alloca (p[i].p_filesz);
-	if (pread64 (memfd, interp, p[i].p_filesz, offset + p[i].p_vaddr)
+       interp = xmalloc (p[i].p_filesz);
+       if (pread (memfd, interp, p[i].p_filesz, offset + p[i].p_vaddr)
 	    != p[i].p_filesz)
-	  {
-	    error (0, 0, gettext ("cannot read program interpreter"));
-	    return EXIT_FAILURE;
-	  }
+         error (EXIT_FAILURE, 0, gettext ("cannot read program interpreter"));
       }
 
   if (list == 0)
@@ -174,14 +159,16 @@ E(find_maps) (pid_t pid, void *auxv, siz
       if (interp == NULL)
 	{
 	  // XXX check whether the executable itself is the loader
-	  return EXIT_FAILURE;
+         exit (EXIT_FAILURE);
 	}
 
       // XXX perhaps try finding ld.so and _r_debug in it
-
-      return EXIT_FAILURE;
+      exit (EXIT_FAILURE);
     }
 
+  free (p);
+  free (interp);
+
   /* Print the PID and program name first.  */
   printf ("%lu:\t%s\n", (unsigned long int) pid, exe);
 
@@ -192,47 +179,27 @@ E(find_maps) (pid_t pid, void *auxv, siz
   do
     {
       struct E(link_map) m;
-      if (pread64 (memfd, &m, sizeof (m), list) != sizeof (m))
-	{
-	  error (0, 0, gettext ("cannot read link map"));
-	  status = EXIT_FAILURE;
-	  goto out;
-	}
+      if (pread (memfd, &m, sizeof (m), list) != sizeof (m))
+       error (EXIT_FAILURE, 0, gettext ("cannot read link map"));
 
       EW(Addr) name_offset = m.l_name;
-    again:
       while (1)
 	{
-	  ssize_t n = pread64 (memfd, tmpbuf.data, tmpbuf.length, name_offset);
+         ssize_t n = pread (memfd, tmpbuf.data, tmpbuf.length, name_offset);
 	  if (n == -1)
-	    {
-	      error (0, 0, gettext ("cannot read object name"));
-	      status = EXIT_FAILURE;
-	      goto out;
-	    }
+           error (EXIT_FAILURE, 0, gettext ("cannot read object name"));
 
 	  if (memchr (tmpbuf.data, '\0', n) != NULL)
 	    break;
 
 	  if (!scratch_buffer_grow (&tmpbuf))
-	    {
-	      error (0, 0, gettext ("cannot allocate buffer for object name"));
-	      status = EXIT_FAILURE;
-	      goto out;
-	    }
+           error (EXIT_FAILURE, 0,
+                  gettext ("cannot allocate buffer for object name"));
 	}
 
-      if (((char *)tmpbuf.data)[0] == '\0' && name_offset == m.l_name
-	  && m.l_libname != 0)
-	{
-	  /* Try the l_libname element.  */
-	  struct E(libname_list) ln;
-	  if (pread64 (memfd, &ln, sizeof (ln), m.l_libname) == sizeof (ln))
-	    {
-	      name_offset = ln.name;
-	      goto again;
-	    }
-	}
+      /* The m.l_name and m.l_libname.name for loader linkmap points to same
+        values (since BZ#387 fix).  Trying to use l_libname name as the
+        shared object name might lead to an infinite loop (BZ#18035).  */
 
       /* Skip over the executable.  */
       if (((char *)tmpbuf.data)[0] != '\0')
@@ -242,7 +209,6 @@ E(find_maps) (pid_t pid, void *auxv, siz
     }
   while (list != 0);
 
- out:
   scratch_buffer_free (&tmpbuf);
   return status;
 }
diff -Nrup a/elf/tst-pldd.c b/elf/tst-pldd.c
--- a/elf/tst-pldd.c	1969-12-31 19:00:00.000000000 -0500
+++ b/elf/tst-pldd.c	2019-05-17 12:35:45.817147947 -0400
@@ -0,0 +1,118 @@
+/* Basic tests for pldd program.
+   Copyright (C) 2019 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <libgen.h>
+#include <stdbool.h>
+
+#include <array_length.h>
+#include <gnu/lib-names.h>
+
+#include <support/subprocess.h>
+#include <support/capture_subprocess.h>
+#include <support/check.h>
+
+static void
+target_process (void *arg)
+{
+  pause ();
+}
+
+/* The test runs in a container because pldd does not support tracing
+   a binary started by the loader iself (as with testrun.sh).  */
+
+static int
+do_test (void)
+{
+  /* Create a copy of current test to check with pldd.  */
+  struct support_subprocess target = support_subprocess (target_process, NULL);
+
+  /* Run 'pldd' on test subprocess.  */
+  struct support_capture_subprocess pldd;
+  {
+    /* Three digits per byte plus null terminator.  */
+    char pid[3 * sizeof (uint32_t) + 1];
+    snprintf (pid, array_length (pid), "%d", target.pid);
+
+    const char prog[] = "/usr/bin/pldd";
+
+    pldd = support_capture_subprogram (prog,
+      (char *const []) { (char *) prog, pid, NULL });
+
+    support_capture_subprocess_check (&pldd, "pldd", 0, sc_allow_stdout);
+  }
+
+  /* Check 'pldd' output.  The test is expected to be linked against only
+     loader and libc.  */
+  {
+    pid_t pid;
+    char buffer[512];
+#define STRINPUT(size) "%" # size "s"
+
+    FILE *out = fmemopen (pldd.out.buffer, pldd.out.length, "r");
+    TEST_VERIFY (out != NULL);
+
+    /* First line is in the form of <pid>: <full path of executable>  */
+    TEST_COMPARE (fscanf (out, "%u: " STRINPUT (512), &pid, buffer), 2);
+
+    TEST_COMPARE (pid, target.pid);
+    TEST_COMPARE (strcmp (basename (buffer), "tst-pldd"), 0);
+
+    /* It expects only one loader and libc loaded by the program.  */
+    bool interpreter_found = false, libc_found = false;
+    while (fgets (buffer, array_length (buffer), out) != NULL)
+      {
+       /* Ignore vDSO.  */
+        if (buffer[0] != '/')
+         continue;
+
+       /* Remove newline so baseline (buffer) can compare against the
+          LD_SO and LIBC_SO macros unmodified.  */
+       if (buffer[strlen(buffer)-1] == '\n')
+         buffer[strlen(buffer)-1] = '\0';
+
+       if (strcmp (basename (buffer), LD_SO) == 0)
+         {
+           TEST_COMPARE (interpreter_found, false);
+           interpreter_found = true;
+           continue;
+         }
+
+       if (strcmp (basename (buffer), LIBC_SO) == 0)
+         {
+           TEST_COMPARE (libc_found, false);
+           libc_found = true;
+           continue;
+         }
+      }
+    TEST_COMPARE (interpreter_found, true);
+    TEST_COMPARE (libc_found, true);
+
+    fclose (out);
+  }
+
+  support_capture_subprocess_free (&pldd);
+  support_process_terminate (&target);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
