fa96cb382c
GDBserver currently hangs forever in waitpid if the leader thread exits before other threads, or if all resumed threads exit - e.g., next over a thread exit with sched-locking on. This is exposed by leader-exit.exp. leader-exit.exp is part of a series of tests for a set of related problems. See <http://www.sourceware.org/ml/gdb-patches/2011-10/msg00704.html>: " To recap, on the Linux kernel, ptrace/waitpid don't allow reaping the leader thread until all other threads in the group are reaped. When the leader exits, it goes zombie, but waitpid will not return an exit status until the other threads are gone. This is presently exercised by the gdb.threads/leader-exit.exp test. The fix for that test, in linux-nat.c:wait_lwp, handles the case where we see the leader gone when we're stopping all threads to report an event to some other thread to the core. (...) The latter bit about not blocking if there no resumed threads in the process also applies to some other thread exiting, not just the main thread. E.g., this test starts a thread, and runs to a breakpoint in that thread: ... (gdb) c Continuing. [New Thread 0x7ffff75a4700 (LWP 23397)] [Switching to Thread 0x7ffff75a4700 (LWP 23397)] Breakpoint 2, thread_a (arg=0x0) at ../../../src/gdb/testsuite/gdb.threads/no-unwaited-for-left.c:28 28 return 0; /* break-here */ (gdb) info threads * 2 Thread 0x7ffff75a4700 (LWP 23397) thread_a (arg=0x0) at ../../../src/gdb/testsuite/gdb.threads/no-unwaited-for-left.c:28 1 Thread 0x7ffff7fcb720 (LWP 23391) 0x00007ffff7bc606d in pthread_join (threadid=140737343276800, thread_return=0x0) at pthread_join.c:89 The thread will exit as soon as we resume it. But if we only resume that thread, leaving the rest of the threads stopped: (gdb) set scheduler-locking on (gdb) c Continuing. ^C^C^C^C^C^C^C^C " This patch fixes the issues by implementing TARGET_WAITKIND_NO_RESUMED on GDBserver, similarly to what the patch above did for native Linux GDB. gdb.threads/leader-exit.exp now passes. gdb.threads/no-unwaited-for-left.exp now at least errors out instead of hanging: continue Continuing. warning: Remote failure reply: E.No unwaited-for children left. [Thread 15454] #1 stopped. 0x00000034cf408e60 in pthread_join (threadid=140737353922368, thread_return=0x0) at pthread_join.c:93 93 lll_wait_tid (pd->tid); (gdb) FAIL: gdb.threads/no-unwaited-for-left.exp: continue stops when the main thread exits The gdb.threads/non-ldr-exc-*.exp tests are skipped because GDBserver unfortunately doesn't support fork/exec yet, but I'm confident this fixes the related issues. I'm leaving modeling TARGET_WAITKIND_NO_RESUMED in the RSP for a separate pass. (BTW, in case of error in response to a vCont, it would be better for GDB to query the target for the current thread, or re-select one, instead of assuming current inferior_ptid is still the selected thread.) This implementation is a little different from GDB's, because I'm avoiding bringing in more of this broken use of waitpid(PID) into GDBserver. Specifically, this avoids waitpid(PID) when stopping all threads. There's really no need for wait_for_sigstop to wait for each LWP in turn. Instead, with some refactoring, we make it reuse linux_wait_for_event. gdb/gdbserver/ 2014-02-27 Pedro Alves <palves@redhat.com> PR 12702 * inferiors.h (A_I_NEXT, ALL_INFERIORS_TYPE, ALL_PROCESSES): New macros. * linux-low.c (delete_lwp, handle_extended_wait): Add debug output. (last_thread_of_process_p): Take a PID argument instead of a thread pointer. (linux_wait_for_lwp): Delete. (num_lwps, check_zombie_leaders, not_stopped_callback): New functions. (linux_low_filter_event): New function, party factored out from linux_wait_for_event. (linux_wait_for_event): Rename to ... (linux_wait_for_event_filtered): ... this. Add new filter ptid argument. Partly rewrite. Always use waitpid(-1, WNOHANG) and sigsuspend. Check for zombie leaders. (linux_wait_for_event): Reimplement as wrapper around linux_wait_for_event_filtered. (linux_wait_1): Handle TARGET_WAITKIND_NO_RESUMED. Assume that if a normal or signal exit is seen, it's the whole process exiting. (wait_for_sigstop): No longer a for_each_inferior callback. Rewrite on top of linux_wait_for_event_filtered. (stop_all_lwps): Call wait_for_sigstop directly. * server.c (resume, handle_target_event): Handle TARGET_WAITKIND_NO_RESUMED. |
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| ChangeLog | ||
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README
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.