c2c118cfe1
There's code in linux_wait_1 that resumes all threads if the Hc thread
disappears. It's the wrong thing to do, as GDB has told GDBserver to
resume only one thread, because e.g., the user has scheduler-locking
enabled, or because GDB was stepping the program over a breakpoint.
Resuming all threads behind GDB's back can't be good in either case.
The right thing to do is to detect that that the (only) resumed thread
is gone, and let GDB know about it. The Linux backend is already
doing that nowadays, since:
commit fa96cb382c12b099675c5cc238aaa7352a3fd3d7
Author: Pedro Alves <palves@redhat.com>
AuthorDate: Thu Feb 27 14:30:08 2014 +0000
Teach GDBserver's Linux backend about no unwaited-for children (TARGET_WAITKIND_NO_RESUMED).
The backend detects that all resumed threads have disappeared, and
returns TARGET_WAITKIND_NO_RESUMED to the core of GDBserver, which
then reports an error to GDB.
There's no need to frob the passed in ptid to wait for the continue
thread either -- linux_wait_for_event only returns events for resumed
threads.
The badness (of resuming threads) can actually be observed in the
testsuite, if we force-disable vCont support in GDBserver -- before
the patch, gdb.threads/no-unwaited-for-left.exp hangs if we disable
vCont:
(gdb) continue
Continuing.
FAIL: gdb.threads/no-unwaited-for-left.exp: continue to breakpoint: break-here (timeout)
... more cascading timeouts ....
After the patch, gdb.threads/no-unwaited-for-left.exp behaves the same
with or without vCont support:
(gdb) continue
Continuing.
[New Thread 32226]
[Switching to Thread 32226]
Breakpoint 2, thread_a (arg=0x0) at /home/pedro/gdb/mygit/build/../src/gdb/testsuite/gdb.threads/no-unwaited-for-left.c:28
28 return 0; /* break-here */
(gdb) PASS: gdb.threads/no-unwaited-for-left.exp: continue to breakpoint: break-here
...
continue
Continuing.
warning: Remote failure reply: E.No unwaited-for children left.
[Thread 32222] #1 stopped.
(gdb) FAIL: gdb.threads/no-unwaited-for-left.exp: continue stops when the main thread exits
Overall, this is also good for getting rid of a RSP detail from the backend.
gdb/gdbserver/
2014-11-12 Pedro Alves <palves@redhat.com>
* linux-low.c (linux_wait_1): Don't force a wait for the Hc
thread, and don't resume all threads if the Hc thread has exited.
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.