Pedro Alves
f0db101d98
In all-stop mode, if the current thread disappears while stopping all threads, gdbserver calls set_desired_thread(0) ['0' means "I want the continue thread"] which just picks the first thread in the list. This looks like a dangerous thing to do. GDBserver continues processing whatever it was doing, but to the wrong thread. If debugging more than one process, we may even pick the wrong process. Instead, GDBserver should detect the situation and bail out of whatever is was doing. The backends used to pay attention to the set 'cont_thread' (the Hc thread, used in the old way to resume threads, before vCont), but all such 'cont_thread' checks have been eliminated meanwhile. The remaining implicit dependencies that I found on there being a selected thread in the backends are in the Ctrl-C handling, which some backends use as thread to send a signal to. Even that seems to me to be better handled by always using the first thread in the list or by using the signal_pid PID. In order to make this a systematic approach, I'm making set_desired_thread never fallback to a random thread, and instead end up with current_thread == NULL, like already done in non-stop mode. Then I updated all callers to handle the situation. I stumbled on this while fixing other bugs exposed by gdb.threads/fork-plus-threads.exp test. The problems I saw were fixed in a different way, but in any case, I think the potential for problems is more or less obvious, and the resulting code looks a bit less magical to me. Tested on x86-64 Fedora 20, w/ native-extended-gdbserver board. gdb/gdbserver/ChangeLog: 2015-08-21 Pedro Alves <palves@redhat.com> * linux-low.c (wait_for_sigstop): Always switch to no thread selected if the previously current thread dies. * lynx-low.c (lynx_request_interrupt): Use the first thread's process instead of the current thread's. * remote-utils.c (input_interrupt): Don't check if there's no current thread. * server.c (gdb_read_memory, gdb_write_memory): If setting the current thread to the general thread fails, error out. (handle_qxfer_auxv, handle_qxfer_libraries) (handle_qxfer_libraries_svr4, handle_qxfer_siginfo) (handle_qxfer_spu, handle_qxfer_statictrace, handle_qxfer_fdpic) (handle_query): Check if there's a thread selected instead of checking whether there's any thread in the thread list. (handle_qxfer_threads, handle_qxfer_btrace) (handle_qxfer_btrace_conf): Don't error out early if there's no thread in the thread list. (handle_v_cont, myresume): Don't set the current thread to the continue thread. (process_serial_event) <Hg handling>: Also set thread_id if the previous general thread is still alive. (process_serial_event) <g/G handling>: If setting the current thread to the general thread fails, error out. * spu-low.c (spu_resume, spu_request_interrupt): Use the first thread's lwp instead of the current thread's. * target.c (set_desired_thread): If the desired thread was not found, leave the current thread pointing to NULL. Return an int (boolean) indicating success. * target.h (set_desired_thread): Change return type to int.
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.