Fix backwards compatibility with old GDBservers (PR remote/22597)
At <https://sourceware.org/ml/gdb-patches/2017-12/msg00285.html>,
Maciej reported that commit:
commit 5cd63fda035d4ba949e6478406162c4673b3c9ef
Date: Wed Oct 4 18:21:10 2017 +0100
Subject: Fix "Remote 'g' packet reply is too long" problems with multiple inferiors
made GDB stop working with older stubs. Any attempt to continue
execution after the initial connection fails with:
[...]
Process .../gdb/testsuite/outputs/gdb.base/advance/advance created; pid = 2670
Listening on port 2346
target remote [...]:2346
Remote debugging using [...]:2346
Reading symbols from .../lib64/ld.so.1...done.
[Switching to Thread <main>]
(gdb) continue
Cannot execute this command without a live selected thread.
(gdb)
The problem is:
(gdb) c
Cannot execute this command without a live selected thread.
(gdb) info threads
Id Target Id Frame
1 Thread 14917 0x00007f341cd98ed0 in _start () from /lib64/ld-linux-x86-64.so.2
The current thread <Thread ID 2> has terminated. See `help thread'.
^^^^^^^^^^^
(gdb)
Note, thread _2_. There's really only one thread in the inferior
(it's still at the entry point), but still GDB added a bogus second
thread.
The reason GDB started adding a second thread after 5cd63fda035d is
this hunk:
+ if (event->ptid == null_ptid)
+ {
+ const char *thr = strstr (p1 + 1, ";thread:");
+ if (thr != NULL)
+ event->ptid = read_ptid (thr + strlen (";thread:"),
+ NULL);
+ else
+ event->ptid = magic_null_ptid;
+ }
Note the else branch that falls back to magic_null_ptid. We reach
that when we process the initial stop reply sent back in response to
the the "?" (status) packet early in the connection setup:
Sending packet: $?#3f...Ack
Packet received: T0506:0000000000000000;07:40a510f4fd7f0000;10:d0fe1201577f0000;
And note that that response does not include a ";thread:XXX" part.
This stop reply is processed after listing threads with qfThreadInfo /
qsThreadInfo :
Sending packet: $qfThreadInfo#bb...Ack
Packet received: m3915
Sending packet: $qsThreadInfo#c8...Ack
Packet received: l
meaning, when we process that stop reply, we treat the event as coming
from a thread with ptid == magic_null_ptid, which is not yet in the
thread list, so we add it then:
(top-gdb) p ptid
$1 = {m_pid = 42000, m_lwp = -1, m_tid = 1}
(top-gdb) bt
#0 0x0000000000840a8c in add_thread_silent(ptid_t) (ptid=...) at src/gdb/thread.c:269
#1 0x00000000007ad61d in remote_add_thread(ptid_t, int, int) (ptid=..., running=0, executing=0)
at src/gdb/remote.c:1838
#2 0x00000000007ad8de in remote_notice_new_inferior(ptid_t, int) (currthread=..., executing=0)
at src/gdb/remote.c:1921
#3 0x00000000007b758b in process_stop_reply(stop_reply*, target_waitstatus*) (stop_reply=0x1158860, status=0x7fffffffcc00)
at src/gdb/remote.c:7217
#4 0x00000000007b7a38 in remote_wait_as(ptid_t, target_waitstatus*, int) (ptid=..., status=0x7fffffffcc00, options=0)
at src/gdb/remote.c:7380
#5 0x00000000007b7cd1 in remote_wait(target_ops*, ptid_t, target_waitstatus*, int) (ops=0x102fac0 <remote_ops>, ptid=..., status=0x7fffffffcc00, options=0) at src/gdb/remote.c:7446
#6 0x000000000081587b in delegate_wait(target_ops*, ptid_t, target_waitstatus*, int) (self=0x102fac0 <remote_ops>, arg1=..., arg2=0x7fffffffcc00, arg3=0) at src/gdb/target-delegates.c:138
#7 0x0000000000827d77 in target_wait(ptid_t, target_waitstatus*, int) (ptid=..., status=0x7fffffffcc00, options=0)
at src/gdb/target.c:2179
#8 0x0000000000715fda in do_target_wait(ptid_t, target_waitstatus*, int) (ptid=..., status=0x7fffffffcc00, options=0)
at src/gdb/infrun.c:3589
#9 0x0000000000716351 in wait_for_inferior() () at src/gdb/infrun.c:3707
#10 0x0000000000715435 in start_remote(int) (from_tty=1) at src/gdb/infrun.c:3212
things go downhill from this.
We don't see the problem with current master gdbserver, because that
version always sends the ";thread:" part in the initial stop reply:
Sending packet: $?#3f...Packet received: T0506:0000000000000000;07:a0d4ffffff7f0000;10:d05eddf7ff7f0000;thread:p3cea.3cea;core:3;
Years ago I had added a "--disable-packet=" command line option to
gdbserver which comes in handy for testing this, since the existing
"--disable-packet=Tthread" precisely makes gdbserver not send that
";thread:" part in stop replies. The testcase added by this commit
emulates old gdbserver making use of that.
I've compared a testrun at 5cd63fda035d^ (before regression) with
'current master+patch', against old gdbserver at f8b73d13b7ca^. I
hacked out --once, and "monitor exit" to be able to test. The results
are a bit too unstable to tell accurately, but it looked like there
were no regressions. Maciej confirmed this worked for him as well.
No regressions on master (against master gdbserver).
gdb/ChangeLog:
2018-01-11 Pedro Alves <palves@redhat.com>
PR remote/22597
* remote.c (remote_parse_stop_reply): Default to the last-set
general thread instead of to 'magic_null_ptid'.
gdb/testsuite/ChangeLog:
2018-01-11 Pedro Alves <palves@redhat.com>
PR remote/22597
* gdb.server/stop-reply-no-thread.c: New file.
* gdb.server/stop-reply-no-thread.exp: New file.
2018-01-11 01:23:04 +01:00
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/* This testcase is part of GDB, the GNU debugger.
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2019-01-01 07:01:51 +01:00
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Copyright 2018-2019 Free Software Foundation, Inc.
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Fix backwards compatibility with old GDBservers (PR remote/22597)
At <https://sourceware.org/ml/gdb-patches/2017-12/msg00285.html>,
Maciej reported that commit:
commit 5cd63fda035d4ba949e6478406162c4673b3c9ef
Date: Wed Oct 4 18:21:10 2017 +0100
Subject: Fix "Remote 'g' packet reply is too long" problems with multiple inferiors
made GDB stop working with older stubs. Any attempt to continue
execution after the initial connection fails with:
[...]
Process .../gdb/testsuite/outputs/gdb.base/advance/advance created; pid = 2670
Listening on port 2346
target remote [...]:2346
Remote debugging using [...]:2346
Reading symbols from .../lib64/ld.so.1...done.
[Switching to Thread <main>]
(gdb) continue
Cannot execute this command without a live selected thread.
(gdb)
The problem is:
(gdb) c
Cannot execute this command without a live selected thread.
(gdb) info threads
Id Target Id Frame
1 Thread 14917 0x00007f341cd98ed0 in _start () from /lib64/ld-linux-x86-64.so.2
The current thread <Thread ID 2> has terminated. See `help thread'.
^^^^^^^^^^^
(gdb)
Note, thread _2_. There's really only one thread in the inferior
(it's still at the entry point), but still GDB added a bogus second
thread.
The reason GDB started adding a second thread after 5cd63fda035d is
this hunk:
+ if (event->ptid == null_ptid)
+ {
+ const char *thr = strstr (p1 + 1, ";thread:");
+ if (thr != NULL)
+ event->ptid = read_ptid (thr + strlen (";thread:"),
+ NULL);
+ else
+ event->ptid = magic_null_ptid;
+ }
Note the else branch that falls back to magic_null_ptid. We reach
that when we process the initial stop reply sent back in response to
the the "?" (status) packet early in the connection setup:
Sending packet: $?#3f...Ack
Packet received: T0506:0000000000000000;07:40a510f4fd7f0000;10:d0fe1201577f0000;
And note that that response does not include a ";thread:XXX" part.
This stop reply is processed after listing threads with qfThreadInfo /
qsThreadInfo :
Sending packet: $qfThreadInfo#bb...Ack
Packet received: m3915
Sending packet: $qsThreadInfo#c8...Ack
Packet received: l
meaning, when we process that stop reply, we treat the event as coming
from a thread with ptid == magic_null_ptid, which is not yet in the
thread list, so we add it then:
(top-gdb) p ptid
$1 = {m_pid = 42000, m_lwp = -1, m_tid = 1}
(top-gdb) bt
#0 0x0000000000840a8c in add_thread_silent(ptid_t) (ptid=...) at src/gdb/thread.c:269
#1 0x00000000007ad61d in remote_add_thread(ptid_t, int, int) (ptid=..., running=0, executing=0)
at src/gdb/remote.c:1838
#2 0x00000000007ad8de in remote_notice_new_inferior(ptid_t, int) (currthread=..., executing=0)
at src/gdb/remote.c:1921
#3 0x00000000007b758b in process_stop_reply(stop_reply*, target_waitstatus*) (stop_reply=0x1158860, status=0x7fffffffcc00)
at src/gdb/remote.c:7217
#4 0x00000000007b7a38 in remote_wait_as(ptid_t, target_waitstatus*, int) (ptid=..., status=0x7fffffffcc00, options=0)
at src/gdb/remote.c:7380
#5 0x00000000007b7cd1 in remote_wait(target_ops*, ptid_t, target_waitstatus*, int) (ops=0x102fac0 <remote_ops>, ptid=..., status=0x7fffffffcc00, options=0) at src/gdb/remote.c:7446
#6 0x000000000081587b in delegate_wait(target_ops*, ptid_t, target_waitstatus*, int) (self=0x102fac0 <remote_ops>, arg1=..., arg2=0x7fffffffcc00, arg3=0) at src/gdb/target-delegates.c:138
#7 0x0000000000827d77 in target_wait(ptid_t, target_waitstatus*, int) (ptid=..., status=0x7fffffffcc00, options=0)
at src/gdb/target.c:2179
#8 0x0000000000715fda in do_target_wait(ptid_t, target_waitstatus*, int) (ptid=..., status=0x7fffffffcc00, options=0)
at src/gdb/infrun.c:3589
#9 0x0000000000716351 in wait_for_inferior() () at src/gdb/infrun.c:3707
#10 0x0000000000715435 in start_remote(int) (from_tty=1) at src/gdb/infrun.c:3212
things go downhill from this.
We don't see the problem with current master gdbserver, because that
version always sends the ";thread:" part in the initial stop reply:
Sending packet: $?#3f...Packet received: T0506:0000000000000000;07:a0d4ffffff7f0000;10:d05eddf7ff7f0000;thread:p3cea.3cea;core:3;
Years ago I had added a "--disable-packet=" command line option to
gdbserver which comes in handy for testing this, since the existing
"--disable-packet=Tthread" precisely makes gdbserver not send that
";thread:" part in stop replies. The testcase added by this commit
emulates old gdbserver making use of that.
I've compared a testrun at 5cd63fda035d^ (before regression) with
'current master+patch', against old gdbserver at f8b73d13b7ca^. I
hacked out --once, and "monitor exit" to be able to test. The results
are a bit too unstable to tell accurately, but it looked like there
were no regressions. Maciej confirmed this worked for him as well.
No regressions on master (against master gdbserver).
gdb/ChangeLog:
2018-01-11 Pedro Alves <palves@redhat.com>
PR remote/22597
* remote.c (remote_parse_stop_reply): Default to the last-set
general thread instead of to 'magic_null_ptid'.
gdb/testsuite/ChangeLog:
2018-01-11 Pedro Alves <palves@redhat.com>
PR remote/22597
* gdb.server/stop-reply-no-thread.c: New file.
* gdb.server/stop-reply-no-thread.exp: New file.
2018-01-11 01:23:04 +01:00
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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int
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main ()
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{
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return 0;
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}
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