Function restoreUserLDPRELOAD

src/dmtcpworker.cpp:60–116

NOTE: Please keep this function in sync with its copy at: * dmtcp_nocheckpoint.cpp:restoreUserLDPRELOAD() */

 *   dmtcp_nocheckpoint.cpp:restoreUserLDPRELOAD()
 */
void
restoreUserLDPRELOAD()
{
  /* A call to setenv() can result in a call to malloc(). The setenv() call may
   * also grab a low-level libc lock before calling malloc. The malloc()
   * wrapper, if present, will try to acquire the wrapper lock. This can lead
   * to a deadlock in the following scenario:
   *
   * T1 (main thread): fork() -> acquire exclusive lock
   * T2 (ckpt thread): setenv() -> acquire low-level libc lock ->
   *                   malloc -> wait for wrapper-exec lock.
   * T1: setenv() -> block on low-level libc lock (held by T2).
   *
   * The simpler solution would have been to not call setenv from DMTCP, and
   * use putenv instead. This would require larger change.
   *
   * The solution used here is to set LD_PRELOAD to "" before * user main().
   * This is as good as unsetting it.  Later, the ckpt-thread * can unset it
   * if it is still NULL, but then there is a possibility of a race between
   * user code and ckpt-thread.
   */

  // We have now successfully used LD_PRELOAD to execute prior to main()
  // Next, hide our value of LD_PRELOAD, in a global variable.
  // At checkpoint and restart time, we will no longer need our LD_PRELOAD.
  // We will need it in only one place:
  // when the user application makes an exec call:
  // If anybody calls our execwrapper, we will reset LD_PRELOAD then.
  // EXCEPTION:  If anybody directly calls _real_execve with env arg of NULL,
  // they will not be part of DMTCP computation.
  // This has the advantage that our value of LD_PRELOAD will always come
  // before any paths set by user application.
  // Also, bash likes to keep its own envp, but we will interact with bash only
  // within the exec wrapper.
  // NOTE:  If the user called exec("ssh ..."), we currently catch this in
  // src/pugin/dmtcp_ssh.cp:main(), and edit this into
  // exec("dmtcp_launch ... dmtcp_ssh ..."), and re-execute.
  // NOTE:  If the user called exec("dmtcp_nocheckpoint ..."), we will
  // reset LD_PRELOAD back to ENV_VAR_ORIG_LD_PRELOAD in dmtcp_nocheckpoint
  char *preload = getenv("LD_PRELOAD");
  char *userPreload = getenv(ENV_VAR_ORIG_LD_PRELOAD);

  JASSERT(userPreload == NULL || strlen(userPreload) <= strlen(preload))
  (preload)(userPreload);

  // Destructively modify environment variable "LD_PRELOAD" in place:
  preload[0] = '\0';
  if (userPreload == NULL) {
    // _dmtcp_unsetenv("LD_PRELOAD");
  } else {
    strcat(preload, userPreload);

    // setenv("LD_PRELOAD", userPreload, 1);
  }
  JTRACE("LD_PRELOAD") (preload) (userPreload) (getenv(ENV_VAR_HIJACK_LIBS))
    (getenv(ENV_VAR_HIJACK_LIBS_M32)) (getenv("LD_PRELOAD"));
}