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On some systems, the gdb.multi/multi-target.exp testcase occasionally fails like so: Running src/gdb/testsuite/gdb.multi/multi-target.exp ... FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 1: info connections FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 1: info inferiors FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 2: info connections FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 2: info inferiors FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 3: inferior 3 ... many more cascading fails. The problem starts when the testcase runs an inferior against GDBserver: (gdb) run Starting program: build/gdb/testsuite/outputs/gdb.multi/multi-target/multi-target Reading /lib64/ld-linux-x86-64.so.2 from remote target... warning: File transfers from remote targets can be slow. Use "set sysroot" to access files locally instead. Reading /lib64/ld-linux-x86-64.so.2 from remote target... Reading /lib64/ld-2.31.so from remote target... Reading /lib64/.debug/ld-2.31.so from remote target... Reading /usr/lib/debug//lib64/ld-2.31.so from remote target... Reading /usr/lib/debug/lib64//ld-2.31.so from remote target... Reading target:/usr/lib/debug/lib64//ld-2.31.so from remote target... Reading /lib/x86_64-linux-gnu/libpthread.so.0 from remote target... Reading /lib/x86_64-linux-gnu/libc.so.6 from remote target... Reading /lib/x86_64-linux-gnu/libc-2.31.so from remote target... Reading /lib/x86_64-linux-gnu/.debug/libc-2.31.so from remote target... Reading /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.31.so from remote target... Reading /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.31.so from remote target... Remote connection closed ... Note the "Remote connection closed" message. That means GDBserver exited abruptly. I traced it down to the fact that GDB fetches the thread list from GDBserver while the main thread of the process is still running. On my main system where I wrote the testcase, I have not observed the failure because it is slow enough that the thread stops before GDBserver fetches the thread list in the problem scenario which I'll describe below. With some --remote-debug logging from GDBserver side, we see the last packets before the connection closes: ... getpkt ("vCont;c"); [no ack sent] putpkt ("$OK#9a"); [noack mode] getpkt ("Tp10f9a.10f9a"); [no ack sent] putpkt ("$OK#9a"); [noack mode] getpkt ("Hgp0.0"); [no ack sent] putpkt ("$OK#9a"); [noack mode] getpkt ("qXfer:threads:read::0,1000"); [no ack sent] Note the vCont;c , which sets the program running, and then a qXfer:threads:read packet at the end. The problem happens when the thread list refresh (qXfer:threads:read) is sent just while the main thread is running and it still hasn't initialized its libpthread id internally. In that state, the main thread's lwp will remain with the thread_known flag clear. See in find_one_thread: /* If the new thread ID is zero, a final thread ID will be available later. Do not enable thread debugging yet. */ if (ti.ti_tid == 0) return 0; Now, back in server.cc, to handle the qXfer:threads:read, we reach handle_qxfer_threads -> handle_qxfer_threads_proper, and the latter then calls handle_qxfer_threads_worker for each known thread. In handle_qxfer_threads_worker, we call target_thread_handle. This ends up in thread_db_thread_handle, here: if (!lwp->thread_known && !find_one_thread (thread->id)) return false; Since the thread ID isn't known yet, we call find_one_thread. This calls into libthread_db.so, which accesses memory. Because the current thread is running, that fails and we throw an error, here: /* Get information about this thread. */ err = thread_db->td_ta_map_lwp2thr_p (thread_db->thread_agent, lwpid, &th); if (err != TD_OK) error ("Cannot get thread handle for LWP %d: %s", lwpid, thread_db_err_str (err)); The current design is that whenever GDB-facing packets/requests need to accesses memory, server.cc is supposed to prepare the target for the access. See gdb_read_memory / gdb_write_memory. This preparation means pausing threads if in non-stop mode (someday we could lift this requirement, but we will still need to pause to access registers or do other related ptrace accesses like PTRACE_GET_THREAD_AREA). Note that the multi-target.exp testcase forces "maint set target-non-stop on". So the fix here is to prepare the target to access memory when handling qXfer:threads:read too. gdbserver/ChangeLog: * inferiors.cc (switch_to_process): New, moved here from thread-db.cc, and made extern. * inferiors.h (switch_to_process): Declare. * server.cc: Include "gdbsupport/scoped_restore.h". (handle_qxfer_threads_proper): Now returns bool. Prepare to access memory around target calls. (handle_qxfer_threads): Handle errors. * thread-db.cc (switch_to_process): Moved to inferiors.cc. |
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bfd | ||
binutils | ||
config | ||
contrib | ||
cpu | ||
elfcpp | ||
etc | ||
gas | ||
gdb | ||
gdbserver | ||
gdbsupport | ||
gnulib | ||
gold | ||
gprof | ||
include | ||
intl | ||
ld | ||
libctf | ||
libdecnumber | ||
libiberty | ||
opcodes | ||
readline | ||
sim | ||
texinfo | ||
zlib | ||
.cvsignore | ||
.gitattributes | ||
.gitignore | ||
ar-lib | ||
ChangeLog | ||
compile | ||
config-ml.in | ||
config.guess | ||
config.rpath | ||
config.sub | ||
configure | ||
configure.ac | ||
COPYING | ||
COPYING3 | ||
COPYING3.LIB | ||
COPYING.LIB | ||
COPYING.LIBGLOSS | ||
COPYING.NEWLIB | ||
depcomp | ||
djunpack.bat | ||
install-sh | ||
libtool.m4 | ||
lt~obsolete.m4 | ||
ltgcc.m4 | ||
ltmain.sh | ||
ltoptions.m4 | ||
ltsugar.m4 | ||
ltversion.m4 | ||
MAINTAINERS | ||
Makefile.def | ||
Makefile.in | ||
Makefile.tpl | ||
makefile.vms | ||
missing | ||
mkdep | ||
mkinstalldirs | ||
move-if-change | ||
multilib.am | ||
README | ||
README-maintainer-mode | ||
setup.com | ||
src-release.sh | ||
symlink-tree | ||
test-driver | ||
ylwrap |
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.