nptl: Decorate thread stack on pthread_create

Linux 4.5 removed thread stack annotations due to the complexity of
computing them [1], and Linux added PR_SET_VMA_ANON_NAME on 5.17
as a way to name anonymous virtual memory areas.

This patch adds decoration on the stack created and used by
pthread_create, for glibc crated thread stack the /proc/self/maps will
now show:

  [anon: glibc: pthread stack: <tid>]

And for user-provided stacks:

  [anon: glibc: pthread user stack: <tid>]

The guard page is not decorated, and the mapping name is cleared when
the thread finishes its execution (so the cached stack does not have any
name associated).

Checked on x86_64-linux-gnu aarch64 aarch64-linux-gnu.

[1] 65376df582

Co-authored-by: Ian Rogers <irogers@google.com>
Reviewed-by: DJ Delorie <dj@redhat.com>

elf/Makefile

@@ -303,6 +303,7 @@ tests := \
   tst-array4 \
   tst-array5 \
   tst-auxv \
+  tst-decorate-maps \
   tst-dl-hash \
   tst-leaks1 \
   tst-stringtable \
@@ -2980,3 +2981,5 @@ LDFLAGS-tst-dlclose-lazy-mod1.so = -Wl,-z,lazy,--no-as-needed
 $(objpfx)tst-dlclose-lazy-mod1.so: $(objpfx)tst-dlclose-lazy-mod2.so
 $(objpfx)tst-dlclose-lazy.out: \
   $(objpfx)tst-dlclose-lazy-mod1.so $(objpfx)tst-dlclose-lazy-mod2.so
+
+$(objpfx)tst-decorate-maps: $(shared-thread-library)

elf/tst-decorate-maps.c

@@ -0,0 +1,160 @@
+/* Check the VMA name decoration.
+   Copyright (C) 2023 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 <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/test-driver.h>
+#include <support/xstdio.h>
+#include <support/xthread.h>
+#include <support/xunistd.h>
+#include <sys/mman.h>
+
+#ifndef MAP_STACK
+# define MAP_STACK 0
+#endif
+
+static pthread_barrier_t b;
+
+static void *
+tf (void *closure)
+{
+  /* Wait the thread startup, so thread stack is allocated.  */
+  xpthread_barrier_wait (&b);
+
+  /* Wait the test to read the process mapping.  */
+  xpthread_barrier_wait (&b);
+
+  return NULL;
+}
+
+struct proc_maps_t
+{
+  int n_def_threads;
+  int n_user_threads;
+};
+
+static struct proc_maps_t
+read_proc_maps (void)
+{
+  if (test_verbose)
+    printf ("=== print process %jd memory mapping ===\n",
+	    (intmax_t) getpid ());
+  struct proc_maps_t r = { 0 };
+
+  FILE *f = xfopen ("/proc/self/maps", "r");
+  char *line = NULL;
+  size_t line_len = 0;
+  while (xgetline (&line, &line_len, f))
+    {
+      if (test_verbose)
+	printf ("%s", line);
+      if (strstr (line, "[anon: glibc: pthread stack:") != NULL)
+	r.n_def_threads++;
+      else if (strstr (line, "[anon: glibc: pthread user stack:") != NULL)
+	r.n_user_threads++;
+    }
+  free (line);
+  xfclose (f);
+
+  if (test_verbose)
+    printf ("===\n");
+  return r;
+}
+
+static void
+do_test_threads (bool set_guard)
+{
+  enum
+    {
+      num_def_threads  = 8,
+      num_user_threads = 2,
+      num_threads = num_def_threads + num_user_threads,
+    };
+
+  xpthread_barrier_init (&b, NULL, num_threads + 1);
+
+  pthread_t thr[num_threads];
+  {
+    int i = 0;
+    for (; i < num_threads - num_user_threads; i++)
+      {
+	pthread_attr_t attr;
+	xpthread_attr_init (&attr);
+	/* The guard page is not annotated.  */
+	if (!set_guard)
+	  xpthread_attr_setguardsize (&attr, 0);
+	thr[i] = xpthread_create (&attr, tf, NULL);
+	xpthread_attr_destroy (&attr);
+      }
+    for (; i < num_threads; i++)
+      {
+	pthread_attr_t attr;
+	xpthread_attr_init (&attr);
+	size_t stacksize = support_small_thread_stack_size ();
+	void *stack = xmmap (0,
+			     stacksize,
+			     PROT_READ | PROT_WRITE,
+			     MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK,
+			     -1);
+	xpthread_attr_setstack (&attr, stack, stacksize);
+	if (!set_guard)
+	  xpthread_attr_setguardsize (&attr, 0);
+	thr[i] = xpthread_create (&attr, tf, NULL);
+	xpthread_attr_destroy (&attr);
+      }
+  }
+
+  /* Wait all threads to finshed statup and stack allocation.  */
+  xpthread_barrier_wait (&b);
+
+  {
+    struct proc_maps_t r = read_proc_maps ();
+    TEST_COMPARE (r.n_def_threads, num_def_threads);
+    TEST_COMPARE (r.n_user_threads, num_user_threads);
+  }
+
+  /* Let the threads finish.  */
+  xpthread_barrier_wait (&b);
+
+  for (int i = 0; i < num_threads; i++)
+    xpthread_join (thr[i]);
+
+  {
+    struct proc_maps_t r = read_proc_maps ();
+    TEST_COMPARE (r.n_def_threads, 0);
+    TEST_COMPARE (r.n_user_threads, 0);
+  }
+}
+
+static int
+do_test (void)
+{
+  support_need_proc ("Reads /proc/self/maps to get stack names.");
+
+  if (!support_set_vma_name_supported ())
+    FAIL_UNSUPPORTED ("kernel does not support PR_SET_VMA_ANON_NAME");
+
+  do_test_threads (false);
+  do_test_threads (true);
+
+  return 0;
+}
+
+#include <support/test-driver.c>

nptl/allocatestack.c

@@ -33,6 +33,8 @@
 #include <nptl-stack.h>
 #include <libc-lock.h>
 #include <tls-internal.h>
+#include <intprops.h>
+#include <setvmaname.h>
 
 /* Default alignment of stack.  */
 #ifndef STACK_ALIGN
@@ -577,3 +579,41 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
 
   return 0;
 }
+
+/* Maximum supported name from initial kernel support, not exported
+   by user API.  */
+#define ANON_VMA_NAME_MAX_LEN 80
+
+#define SET_STACK_NAME(__prefix, __stack, __stacksize, __tid)		\
+  ({									\
+     char __stack_name[sizeof (__prefix) +				\
+		       INT_BUFSIZE_BOUND (unsigned int)];		\
+     _Static_assert (sizeof __stack_name <= ANON_VMA_NAME_MAX_LEN,	\
+		     "VMA name size larger than maximum supported");	\
+     __snprintf (__stack_name, sizeof (__stack_name), __prefix "%u",	\
+		 (unsigned int) __tid);					\
+     __set_vma_name (__stack, __stacksize, __stack_name);		\
+   })
+
+/* Add or remove an associated name to the PD VMA stack.  */
+static void
+name_stack_maps (struct pthread *pd, bool set)
+{
+#if _STACK_GROWS_DOWN && !defined(NEED_SEPARATE_REGISTER_STACK)
+  void *stack = pd->stackblock + pd->guardsize;
+#else
+  void *stack = pd->stackblock;
+#endif
+  size_t stacksize = pd->stackblock_size - pd->guardsize;
+
+  if (!set)
+    __set_vma_name (stack, stacksize, NULL);
+  else
+    {
+      unsigned int tid = pd->tid;
+      if (pd->user_stack)
+	SET_STACK_NAME (" glibc: pthread user stack: ", stack, stacksize, tid);
+      else
+	SET_STACK_NAME (" glibc: pthread stack: ", stack, stacksize, tid);
+    }
+}

nptl/pthread_create.c

@@ -369,6 +369,9 @@ start_thread (void *arg)
   /* Initialize pointers to locale data.  */
   __ctype_init ();
 
+  /* Name the thread stack if kernel supports it.  */
+  name_stack_maps (pd, true);
+
   /* Register rseq TLS to the kernel.  */
   {
     bool do_rseq = THREAD_GETMEM (pd, flags) & ATTR_FLAG_DO_RSEQ;
@@ -571,6 +574,9 @@ start_thread (void *arg)
     /* Free the TCB.  */
     __nptl_free_tcb (pd);
 
+  /* Remove the associated name from the thread stack.  */
+  name_stack_maps (pd, false);
+
 out:
   /* We cannot call '_exit' here.  '_exit' will terminate the process.