Fix internal warning when "gdb -p xxx"

ps -e | grep a.out
28886 pts/12   00:00:00 a.out
gdb -p 28886
Loaded symbols for /lib64/ld-linux-x86-64.so.2
0x0000003b0ccbc970 in __nanosleep_nocancel () from /lib64/libc.so.6
../../binutils-gdb/gdb/cleanups.c:265: internal-warning: restore_my_cleanups has found a stale cleanup
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n)

The backtrace of this issue:
(gdb) bt
    file=0x8b0c10 "s' failed.", line=265, fmt=0x8b0c38 "nutils-gdb/gdb/cleanups.c",
    ap=0x7fff803e3ed8) at ../../binutils-gdb/gdb/utils.c:748
    fmt=0x8b0c38 "nutils-gdb/gdb/cleanups.c", ap=0x7fff803e3ed8)
    at ../../binutils-gdb/gdb/utils.c:799
    string=0x8b0c38 "nutils-gdb/gdb/cleanups.c") at ../../binutils-gdb/gdb/utils.c:809
    at ../../binutils-gdb/gdb/cleanups.c:265
    at ../../binutils-gdb/gdb/cleanups.c:276
    at ../../binutils-gdb/gdb/exceptions.c:142
    at ../../binutils-gdb/gdb/exceptions.c:203
    command=0x5d5fb8 <attach_command_continuation_free_args+18>, arg=0x7fff803e525b "2914",
    from_tty=1, mask=RETURN_MASK_ALL) at ../../binutils-gdb/gdb/exceptions.c:549
---Type <return> to continue, or q <return> to quit---
    func_args=0x7fff803e4280, errstring=0x8cf2e4 "/local/bin", mask=RETURN_MASK_ALL)
    at ../../binutils-gdb/gdb/exceptions.c:522

This is a new issue.  It is introduced by commit https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=8bc2fe488957946d2cdccda3ce8d4f39e4003ea0
It removed the discard_cleanups (back_to) inside attach_command.
Then restore_my_cleanups will throw a internal_warning.

https://sourceware.org/ml/gdb-patches/2014-03/msg00374.html

2014-03-21  Hui Zhu  <hui@codesourcery.com>
	    Pedro Alves  <palves@redhat.com>

	* darwin-nat.c (darwin_pid_to_exec_file): Change xmalloc to
	static buffer.
	* fbsd-nat.c (fbsd_pid_to_exec_file): Ditto.
	* linux-nat.c (linux_child_pid_to_exec_file): Ditto.
	* nbsd-nat.c (nbsd_pid_to_exec_file): Ditto.

gdb/ChangeLog

@@ -1,3 +1,12 @@
+2014-03-21  Hui Zhu  <hui@codesourcery.com>
+	    Pedro Alves  <palves@redhat.com>
+
+	* darwin-nat.c (darwin_pid_to_exec_file): Change xmalloc to
+	static buffer.
+	* fbsd-nat.c (fbsd_pid_to_exec_file): Ditto.
+	* linux-nat.c (linux_child_pid_to_exec_file): Ditto.
+	* nbsd-nat.c (nbsd_pid_to_exec_file): Ditto.
+
 2014-03-20  Maciej W. Rozycki  <macro@codesourcery.com>
 
 	* mi/mi-interp.c (mi_memory_changed): Avoid using the ISO C99

gdb/darwin-nat.c

@@ -1991,12 +1991,9 @@ set_enable_mach_exceptions (char *args, int from_tty,
 static char *
 darwin_pid_to_exec_file (struct target_ops *self, int pid)
 {
-  char *path;
+  static char path[PATH_MAX];
   int res;
 
-  path = xmalloc (PATH_MAX);
-  make_cleanup (xfree, path);
-
   res = proc_pidinfo (pid, PROC_PIDPATHINFO, 0, path, PATH_MAX);
   if (res >= 0)
     return path;

gdb/fbsd-nat.c

@@ -39,9 +39,9 @@
 char *
 fbsd_pid_to_exec_file (struct target_ops *self, int pid)
 {
-  size_t len = PATH_MAX;
-  char *buf = xcalloc (len, sizeof (char));
-  char *path;
+  ssize_t len = PATH_MAX;
+  static char buf[PATH_MAX];
+  char name[PATH_MAX];
 
 #ifdef KERN_PROC_PATHNAME
   int mib[4];
@@ -54,15 +54,15 @@ fbsd_pid_to_exec_file (struct target_ops *self, int pid)
     return buf;
 #endif
 
-  path = xstrprintf ("/proc/%d/file", pid);
-  if (readlink (path, buf, PATH_MAX - 1) == -1)
+  xsnprintf (name, PATH_MAX, "/proc/%d/exe", pid);
+  len = readlink (name, buf, PATH_MAX - 1);
+  if (len != -1)
     {
-      xfree (buf);
-      buf = NULL;
+      buf[len] = '\0';
+      return buf;
     }
 
-  xfree (path);
-  return buf;
+  return NULL;
 }
 
 static int

gdb/linux-nat.c

@@ -4011,19 +4011,15 @@ linux_nat_thread_name (struct target_ops *self, struct thread_info *thr)
 static char *
 linux_child_pid_to_exec_file (struct target_ops *self, int pid)
 {
-  char *name1, *name2;
+  static char buf[PATH_MAX];
+  char name[PATH_MAX];
 
-  name1 = xmalloc (PATH_MAX);
-  name2 = xmalloc (PATH_MAX);
-  make_cleanup (xfree, name1);
-  make_cleanup (xfree, name2);
-  memset (name2, 0, PATH_MAX);
+  xsnprintf (name, PATH_MAX, "/proc/%d/exe", pid);
+  memset (buf, 0, PATH_MAX);
+  if (readlink (name, buf, PATH_MAX - 1) <= 0)
+    strcpy (buf, name);
 
-  xsnprintf (name1, PATH_MAX, "/proc/%d/exe", pid);
-  if (readlink (name1, name2, PATH_MAX - 1) > 0)
-    return name2;
-  else
-    return name1;
+  return buf;
 }
 
 /* Records the thread's register state for the corefile note

gdb/nbsd-nat.c

@@ -27,17 +27,17 @@
 char *
 nbsd_pid_to_exec_file (struct target_ops *self, int pid)
 {
-  size_t len = PATH_MAX;
-  char *buf = xcalloc (len, sizeof (char));
-  char *path;
+  ssize_t len;
+  static char buf[PATH_MAX];
+  char name[PATH_MAX];
 
-  path = xstrprintf ("/proc/%d/exe", pid);
-  if (readlink (path, buf, PATH_MAX - 1) == -1)
+  xsnprintf (name, PATH_MAX, "/proc/%d/exe", pid);
+  len = readlink (name, buf, PATH_MAX - 1);
+  if (len != -1)
     {
-      xfree (buf);
-      buf = NULL;
+      buf[len] = '\0';
+      return buf;
     }
 
-  xfree (path);
-  return buf;
+  return NULL;
 }