[Bug threads/12628] New: GDB checkpoint can't/shouldn't be possible with multiple threads on Linux

[Bug threads/12628] New: GDB checkpoint can't/shouldn't be possible with multiple threads on Linux

[kevin.pouget at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12628

           Summary: GDB checkpoint can't/shouldn't be possible with
                    multiple threads on Linux
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: threads
        AssignedTo: unassigned@sourceware.org
        ReportedBy: kevin.pouget@gmail.com


According to the man page of `fork':

A process shall be created with a single thread. If a multi-threaded process
calls fork(), the new process shall contain a replica of the calling thread and
its entire address space, possibly including the states of mutexes and other
resources. Consequently, to avoid errors, the child process may only execute
async-signal-safe operations until such time as one of the exec functions is
called. Fork handlers may be established by means of the pthread_atfork()
function in order to maintain application invariants across fork() calls.


Below is a patch which simply forbids to create a checkpoint when GDB knows
that there are multiple threads in the debuggee.


The Man page obviously assumes a kernel-based thread library, so does my patch
(user-level thread libraries should fork correctly), but do we want to handle
this situation? (linux-thread-db.c is -- at least was, a few years ago -- tight
to GlibC's Pthread implementation, so it might be fine to continue on this way.

Cordially,

Kevin

---

diff --git a/gdb/linux-fork.c b/gdb/linux-fork.c
index 7f654af..3eddea4 100644
--- a/gdb/linux-fork.c
+++ b/gdb/linux-fork.c
@@ -628,6 +628,11 @@ checkpoint_command (char *args, int from_tty)
   pid_t retpid;
   struct cleanup *old_chain;

+  /* Ensure that the inferior is not multithreaded. */
+  update_thread_list () ;
+  if (thread_count () > 1)
+    error(_("checkpoint: can't checkpoint multiple threads.")) ;
+  
   /* Make the inferior fork, record its (and gdb's) state.  */

   if (lookup_minimal_symbol ("fork", NULL, NULL) != NULL)

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[Bug threads/12628] GDB checkpoint can't/shouldn't be possible with multiple threads on Linux

[kevin.pouget at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12628

Kevin Pouget <kevin.pouget at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at sourceware    |kevin.pouget at gmail dot
                   |dot org                     |com

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[Bug threads/12628] GDB checkpoint can't/shouldn't be possible with multiple threads on Linux

[cvs-commit at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=12628

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> 2011-09-15 12:47:14 UTC ---
CVSROOT:    /cvs/src
Module name:    src
Changes by:    kpouget@sourceware.org    2011-09-15 12:47:07

Modified files:
    gdb            : ChangeLog linux-fork.c 

Log message:
    2011-09-15  Kevin Pouget  <kevin.pouget@st.com>

    PR threads/12628
    * linux-fork.c (checkpoint_command): Disallow checkpointing of
    processes with multiple threads.
    (inf_has_multiple_thread_cb): New function.
    (inf_has_multiple_threads): New function.

Patches:
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/ChangeLog.diff?cvsroot=src&r1=1.13333&r2=1.13334
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/linux-fork.c.diff?cvsroot=src&r1=1.38&r2=1.39

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[Bug threads/12628] GDB checkpoint can't/shouldn't be possible with multiple threads on Linux

[kevin.pouget at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12628

Kevin Pouget <kevin.pouget at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #3 from Kevin Pouget <kevin.pouget at gmail dot com> 2011-10-05 18:02:36 UTC ---
fixed

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