9b4c5f878f
This patch removes support for thread events if PTRACE_EVENT_CLONE is not supported in GDBServer. Before, on systems that did not support PTRACE_EVENT_CLONE, both GDB and GDBServer coordinated with libthread_db.so to insert breakpoints at magic locations in libpthread.so, in order to break at thread creation and thread death. Simple software single stepping support was implemented to step over these breakpoints in case there was no hardware single stepping support. However, these simple software single stepping implementations were not fit for any other use as discussed in : https://sourceware.org/ml/gdb-patches/2015-04/msg01110.html These too simple implementations conflict with ongoing work to make proper implementations of software single stepping in GDBServer. The problem is that if some implementations are correct and others are not and only there for the thread magic breakpoint, we can't enable features based solely software single step support since some would be broken. To keep the incorrect implementations and allow the new proper ones at the same time we would need to implement fallback code and it quickly becomes ugly and confusing with multiple checks for legacy software single step or proper software single step. However, PTRACE_EVENT_CLONE was first introduced in Linux 2.5.46, released in November 2002. So I think it's reasonable to just remove support for kernels that don't support PTRACE_EVENT_CLONE, and sidestep the libthread_db breakpoints issues entirely. This thread on the mailling list discusses the issue : https://sourceware.org/ml/gdb/2015-10/msg00078.html No regressions, tested on ubuntu 14.04 ARMv7 and x86. With gdbserver-{native,extended} / { -marm -mthumb } gdb/gdbserver/ChangeLog: * linux-low.c (linux_look_up_symbols): Don't call linux_supports_traceclone. * linux-low.h (thread_db_init): Remove use_events argument. * thread-db.c (thread_db_use_event): Remove global variable. (struct thread_db) <td_thr_event_enable_p>: Remove field. (struct thread_db) <td_create_bp>: Remove field. (thread_db_create_event): Remove function. (thread_db_enable_reporting): Likewise. (find_one_thread): Don't check for thread_db_use_events. (attach_thread): Likewise. (thread_db_load_search): Remove td_thr_event_enable_p initialization. (try_thread_db_load_1): Don't check for thread_db_use_events. (thread_db_init): Remove use_events argument and thread events handling. (remove_thread_event_breakpoints): Remove function. (thread_db_detach): Remove call to remove_thred_event_breakpoints. |
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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.