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.

1 files changed, 9 insertions, 9 deletions

diff --git a/gdb/nbsd-nat.c b/gdb/nbsd-nat.c
index 72c471b..133de61 100644
--- a/gdb/nbsd-nat.c
+++ b/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;
 }