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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ---
 * Author: Markus Gutschke
 */

#include "linuxthreads.h"

#ifdef THREADS
#ifdef __cplusplus
extern "C" {
#endif

#include <asm/stat.h>
#include <sched.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/wait.h>

#include <asm/fcntl.h>
#include <asm/posix_types.h>
#include <asm/types.h>
#include <linux/dirent.h>

#include "linux_syscall_support.h"
#include "thread_lister.h"

#ifndef CLONE_UNTRACED
#define CLONE_UNTRACED 0x00800000
#endif


/* Synchronous signals that should not be blocked while in the lister thread.
 */
static const int sync_signals[]  = { SIGABRT, SIGILL, SIGFPE, SIGSEGV, SIGBUS,
                                     SIGXCPU, SIGXFSZ };

/* itoa() is not a standard function, and we cannot safely call printf()
 * after suspending threads. So, we just implement our own copy. A
 * recursive approach is the easiest here.
 */
static char *local_itoa(char *buf, int i) {
  if (i < 0) {
    *buf++ = '-';
    return local_itoa(buf, -i);
  } else {
    if (i >= 10)
      buf = local_itoa(buf, i/10);
    *buf++ = (i%10) + '0';
    *buf   = '\000';
    return buf;
  }
}


/* Wrapper around clone() that runs "fn" on the same stack as the
 * caller! Unlike fork(), the cloned thread shares the same address space.
 * The caller must be careful to use only minimal amounts of stack until
 * the cloned thread has returned.
 * There is a good chance that the cloned thread and the caller will share
 * the same copy of errno!
 */
#ifdef __GNUC__
#if __GNUC__ == 3 && __GNUC_MINOR__ >= 1 || __GNUC__ > 3
/* Try to force this function into a separate stack frame, and make sure
 * that arguments are passed on the stack.
 */
static int local_clone (int (*fn)(void *), void *arg, ...)
  __attribute__ ((noinline));
#endif
#endif

static int local_clone (int (*fn)(void *), void *arg, ...) {
  /* Leave 4kB of gap between the callers stack and the new clone. This
   * should be more than sufficient for the caller to call waitpid() until
   * the cloned thread terminates.
   *
   * It is important that we set the CLONE_UNTRACED flag, because newer
   * versions of "gdb" otherwise attempt to attach to our thread, and will
   * attempt to reap its status codes. This subsequently results in the
   * caller hanging indefinitely in waitpid(), waiting for a change in
   * status that will never happen. By setting the CLONE_UNTRACED flag, we
   * prevent "gdb" from stealing events, but we still expect the thread
   * lister to fail, because it cannot PTRACE_ATTACH to the process that
   * is being debugged. This is OK and the error code will be reported
   * correctly.
   */
  return sys_clone(fn, (char *)&arg - 4096,
                   CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_UNTRACED, arg, 0, 0, 0);
}


/* Local substitute for the atoi() function, which is not necessarily safe

src/linuxthreads.c  view on Meta::CPAN

        }
      }
      NO_INTR(sys_close(proc));
      sig_proc = proc = -1;

      /* If we failed to find any threads, try looking somewhere else in
       * /proc. Maybe, threads are reported differently on this system.
       */
      if (num_threads > 1 || !*++proc_path) {
        NO_INTR(sys_close(marker));
        sig_marker = marker = -1;

        /* If we never found the parent process, something is very wrong.
         * Most likely, we are running in debugger. Any attempt to operate
         * on the threads would be very incomplete. Let's just report an
         * error to the caller.
         */
        if (!found_parent) {
          ResumeAllProcessThreads(num_threads, pids);
          sys__exit(3);
        }

        /* Now we are ready to call the callback,
         * which takes care of resuming the threads for us.
         */
        args->result = args->callback(args->parameter, num_threads,
                                      pids, args->ap);
        args->err = errno;

        /* Callback should have resumed threads, but better safe than sorry  */
        if (ResumeAllProcessThreads(num_threads, pids)) {
          /* Callback forgot to resume at least one thread, report error     */
          args->err    = EINVAL;
          args->result = -1;
        }

        sys__exit(0);
      }
    detach_threads:
      /* Resume all threads prior to retrying the operation                  */
      ResumeAllProcessThreads(num_threads, pids);
      sig_pids = NULL;
      num_threads = 0;
      sig_num_threads = num_threads;
      max_threads += 100;
    }
  }
}


/* This function gets the list of all linux threads of the current process
 * passes them to the 'callback' along with the 'parameter' pointer; at the
 * call back call time all the threads are paused via
 * PTRACE_ATTACH.
 * The callback is executed from a separate thread which shares only the
 * address space, the filesystem, and the filehandles with the caller. Most
 * notably, it does not share the same pid and ppid; and if it terminates,
 * the rest of the application is still there. 'callback' is supposed to do
 * or arrange for ResumeAllProcessThreads. This happens automatically, if
 * the thread raises a synchronous signal (e.g. SIGSEGV); asynchronous
 * signals are blocked. If the 'callback' decides to unblock them, it must
 * ensure that they cannot terminate the application, or that
 * ResumeAllProcessThreads will get called.
 * It is an error for the 'callback' to make any library calls that could
 * acquire locks. Most notably, this means that most system calls have to
 * avoid going through libc. Also, this means that it is not legal to call
 * exit() or abort().
 * We return -1 on error and the return value of 'callback' on success.
 */
int ListAllProcessThreads(void *parameter,
                          ListAllProcessThreadsCallBack callback, ...) {
  char                   altstack_mem[ALT_STACKSIZE];
  struct ListerParams    args;
  pid_t                  clone_pid;
  int                    dumpable = 1, sig;
  struct kernel_sigset_t sig_blocked, sig_old;

  va_start(args.ap, callback);

  /* If we are short on virtual memory, initializing the alternate stack
   * might trigger a SIGSEGV. Let's do this early, before it could get us
   * into more trouble (i.e. before signal handlers try to use the alternate
   * stack, and before we attach to other threads).
   */
  memset(altstack_mem, 0, sizeof(altstack_mem));

  /* Some of our cleanup functions could conceivable use more stack space.
   * Try to touch the stack right now. This could be defeated by the compiler
   * being too smart for it's own good, so try really hard.
   */
  DirtyStack(32768);

  /* Make this process "dumpable". This is necessary in order to ptrace()
   * after having called setuid().
   */
  dumpable = sys_prctl(PR_GET_DUMPABLE, 0);
  if (!dumpable)
    sys_prctl(PR_SET_DUMPABLE, 1);

  /* Fill in argument block for dumper thread                                */
  args.result       = -1;
  args.err          = 0;
  args.altstack_mem = altstack_mem;
  args.parameter    = parameter;
  args.callback     = callback;

  /* Before cloning the thread lister, block all asynchronous signals, as we */
  /* are not prepared to handle them.                                        */
  sys_sigfillset(&sig_blocked);
  for (sig = 0; sig < sizeof(sync_signals)/sizeof(*sync_signals); sig++) {
    sys_sigdelset(&sig_blocked, sync_signals[sig]);
  }
  if (sys_sigprocmask(SIG_BLOCK, &sig_blocked, &sig_old)) {
    args.err = errno;
    args.result = -1;
    goto failed;
  }

  /* scope */ {
    /* After cloning, both the parent and the child share the same instance
     * of errno. We must make sure that at least one of these processes
     * (in our case, the parent) uses modified syscall macros that update
     * a local copy of errno, instead.
     */
    #ifdef __cplusplus
      #define sys0_sigprocmask sys.sigprocmask
      #define sys0_waitpid     sys.waitpid
      SysCalls sys;
    #else
      int my_errno;
      #define SYS_ERRNO        my_errno
      #define SYS_INLINE       inline
      #define SYS_PREFIX       0
      #undef  SYS_LINUX_SYSCALL_SUPPORT_H
      #include "linux_syscall_support.h"
    #endif
  
    int clone_errno;
    clone_pid = local_clone((int (*)(void *))ListerThread, &args);
    clone_errno = errno;

    sys_sigprocmask(SIG_SETMASK, &sig_old, &sig_old);

    if (clone_pid >= 0) {
      int status, rc;
      while ((rc = sys0_waitpid(clone_pid, &status, __WALL)) < 0 &&
             ERRNO == EINTR) {
             /* Keep waiting                                                 */
      }
      if (rc < 0) {
        args.err = ERRNO;
        args.result = -1;
      } else if (WIFEXITED(status)) {
        switch (WEXITSTATUS(status)) {
          case 0: break;             /* Normal process termination           */
          case 2: args.err = EFAULT; /* Some fault (e.g. SIGSEGV) detected   */
                  args.result = -1;
                  break;
          case 3: args.err = EPERM;  /* Process is already being traced      */
                  args.result = -1;
                  break;
          default:args.err = ECHILD; /* Child died unexpectedly              */
                  args.result = -1;
                  break;
        }
      } else if (!WIFEXITED(status)) {
        args.err    = EFAULT;        /* Terminated due to an unhandled signal*/
        args.result = -1;
      }
    } else {
      args.result = -1;
      args.err    = clone_errno;
    }