[binutils-gdb] Fix backwards compatibility with old GDBservers (PR remote/22597)

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[binutils-gdb] Fix backwards compatibility with old GDBservers (PR remote/22597)

sergiodj+buildbot-2
*** TEST RESULTS FOR COMMIT 3cada74087687907311b52781354ff551e10a0ed ***

Author: Pedro Alves <[hidden email]>
Branch: master
Commit: 3cada74087687907311b52781354ff551e10a0ed

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  <[hidden email]>

        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  <[hidden email]>

        PR remote/22597
        * gdb.server/stop-reply-no-thread.c: New file.
        * gdb.server/stop-reply-no-thread.exp: New file.
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Failures on Fedora-i686, branch master

sergiodj+buildbot-2
Buildslave:
        fedora-x86-64-2

Full Build URL:
        <http://gdb-build.sergiodj.net/builders/Fedora-i686/builds/8532>

Commit(s) tested:
        3cada74087687907311b52781354ff551e10a0ed

Author(s) (in the same order as the commits):
        Pedro Alves <[hidden email]>

Subject:
        Fix backwards compatibility with old GDBservers (PR remote/22597)

Testsuite log (gdb.sum and gdb.log) URL(s):
        <http://gdb-build.sergiodj.net/results/Fedora-i686/3c/3cada74087687907311b52781354ff551e10a0ed/>

*** Diff to previous build ***
============================
new FAIL: gdb.gdb/complaints.exp: breakpoint in captured_command_loop
new FAIL: gdb.gdb/complaints.exp: run until breakpoint at captured_command_loop
new FAIL: gdb.gdb/observer.exp: breakpoint in captured_main
new FAIL: gdb.gdb/observer.exp: run until breakpoint at captured_main
new FAIL: gdb.gdb/python-interrupts.exp: breakpoint in captured_command_loop
new FAIL: gdb.gdb/python-interrupts.exp: run until breakpoint at captured_command_loop
new FAIL: gdb.gdb/python-selftest.exp: breakpoint in captured_command_loop
new FAIL: gdb.gdb/python-selftest.exp: run until breakpoint at captured_command_loop
new FAIL: gdb.gdb/selftest.exp: breakpoint in captured_main
new FAIL: gdb.gdb/selftest.exp: run until breakpoint at captured_main
PASS -> FAIL: gdb.linespec/cpls-abi-tag.exp: test_abi_tag: completion: at tag: tab complete "b test_abi_tag_function[abi:"
PASS -> FAIL: gdb.linespec/cpls-abi-tag.exp: test_abi_tag: completion: at tag: cmd complete "b test_abi_tag_function[abi:"
============================


*** Complete list of XFAILs for this builder ***

To obtain the list of XFAIL tests for this builder, go to:

        <http://git.sergiodj.net/?p=gdb-xfails.git;a=blob;f=xfails/Fedora-i686/xfails/master/xfail;hb=e3bd253>

You can also see a pretty-printed version of the list, with more information
about each XFAIL, by going to:

        <http://git.sergiodj.net/?p=gdb-xfails.git;a=blob;f=xfails/Fedora-i686/xfails/master/xfail.table;hb=e3bd253>



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Failures on Fedora-x86_64-m32, branch master

sergiodj+buildbot-2
In reply to this post by sergiodj+buildbot-2
Buildslave:
        fedora-x86-64-4

Full Build URL:
        <http://gdb-build.sergiodj.net/builders/Fedora-x86_64-m32/builds/8508>

Commit(s) tested:
        3cada74087687907311b52781354ff551e10a0ed

Author(s) (in the same order as the commits):
        Pedro Alves <[hidden email]>

Subject:
        Fix backwards compatibility with old GDBservers (PR remote/22597)

Testsuite log (gdb.sum and gdb.log) URL(s):
        <http://gdb-build.sergiodj.net/results/Fedora-x86_64-m32/3c/3cada74087687907311b52781354ff551e10a0ed/>

*** Diff to previous build ***
============================
PASS -> KFAIL: gdb.threads/process-dies-while-handling-bp.exp: non_stop=off: cond_bp_target=1: inferior 1 exited
============================


*** Complete list of XFAILs for this builder ***

To obtain the list of XFAIL tests for this builder, go to:

        <http://git.sergiodj.net/?p=gdb-xfails.git;a=blob;f=xfails/Fedora-x86_64-m32/xfails/master/xfail;hb=93edd57>

You can also see a pretty-printed version of the list, with more information
about each XFAIL, by going to:

        <http://git.sergiodj.net/?p=gdb-xfails.git;a=blob;f=xfails/Fedora-x86_64-m32/xfails/master/xfail.table;hb=93edd57>



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Failures on Fedora-x86_64-native-gdbserver-m64, branch master

sergiodj+buildbot-2
In reply to this post by sergiodj+buildbot-2
Buildslave:
        fedora-x86-64-1

Full Build URL:
        <http://gdb-build.sergiodj.net/builders/Fedora-x86_64-native-gdbserver-m64/builds/8491>

Commit(s) tested:
        3cada74087687907311b52781354ff551e10a0ed

Author(s) (in the same order as the commits):
        Pedro Alves <[hidden email]>

Subject:
        Fix backwards compatibility with old GDBservers (PR remote/22597)

Testsuite log (gdb.sum and gdb.log) URL(s):
        <http://gdb-build.sergiodj.net/results/Fedora-x86_64-native-gdbserver-m64/3c/3cada74087687907311b52781354ff551e10a0ed/>

*** Diff to previous build ***
============================
PASS -> KFAIL: gdb.threads/process-dies-while-handling-bp.exp: non_stop=off: cond_bp_target=1: inferior 1 exited
============================


*** Complete list of XFAILs for this builder ***

To obtain the list of XFAIL tests for this builder, go to:

        <http://git.sergiodj.net/?p=gdb-xfails.git;a=blob;f=xfails/Fedora-x86_64-native-gdbserver-m64/xfails/master/xfail;hb=05dfcb4>

You can also see a pretty-printed version of the list, with more information
about each XFAIL, by going to:

        <http://git.sergiodj.net/?p=gdb-xfails.git;a=blob;f=xfails/Fedora-x86_64-native-gdbserver-m64/xfails/master/xfail.table;hb=05dfcb4>



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Failures on Ubuntu-AArch32-native-extended-gdbserver-m32, branch master

sergiodj+buildbot-2
In reply to this post by sergiodj+buildbot-2
Buildslave:
        ubuntu-trusty-aarch32-1

Full Build URL:
        <http://gdb-build.sergiodj.net/builders/Ubuntu-AArch32-native-extended-gdbserver-m32/builds/2533>

Commit(s) tested:
        3cada74087687907311b52781354ff551e10a0ed

Author(s) (in the same order as the commits):
        Pedro Alves <[hidden email]>

Subject:
        Fix backwards compatibility with old GDBservers (PR remote/22597)

Testsuite log (gdb.sum and gdb.log) URL(s):
        <http://gdb-build.sergiodj.net/results/Ubuntu-AArch32-native-extended-gdbserver-m32/3c/3cada74087687907311b52781354ff551e10a0ed/>

*** Diff to previous build ***
============================
new KFAIL: gdb.base/step-over-syscall.exp: clone: displaced=on: single step over clone
new FAIL: gdb.threads/interrupt-while-step-over.exp: displaced-stepping=off: iter=1: wait for stops
new FAIL: gdb.threads/interrupt-while-step-over.exp: displaced-stepping=off: iter=3: wait for stops
new FAIL: gdb.threads/interrupt-while-step-over.exp: displaced-stepping=off: iter=11: wait for stops
new FAIL: gdb.threads/interrupt-while-step-over.exp: displaced-stepping=off: iter=14: wait for stops
new FAIL: gdb.threads/interrupt-while-step-over.exp: displaced-stepping=off: iter=17: wait for stops
PASS -> KFAIL: gdb.threads/process-dies-while-handling-bp.exp: non_stop=on: cond_bp_target=1: inferior 1 exited
new FAIL: gdb.threads/queue-signal.exp: determine thread functions
============================


*** Complete list of XFAILs for this builder ***

FAILURE TO OBTAIN THE COMMIT FOR THE XFAIL LIST.  PLEASE CONTACT THE BUILDBOT ADMIN.



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Failures on Ubuntu-AArch32-native-gdbserver-m32, branch master

sergiodj+buildbot-2
In reply to this post by sergiodj+buildbot-2
Buildslave:
        ubuntu-trusty-aarch32-1

Full Build URL:
        <http://gdb-build.sergiodj.net/builders/Ubuntu-AArch32-native-gdbserver-m32/builds/2515>

Commit(s) tested:
        3cada74087687907311b52781354ff551e10a0ed

Author(s) (in the same order as the commits):
        Pedro Alves <[hidden email]>

Subject:
        Fix backwards compatibility with old GDBservers (PR remote/22597)

Testsuite log (gdb.sum and gdb.log) URL(s):
        <http://gdb-build.sergiodj.net/results/Ubuntu-AArch32-native-gdbserver-m32/3c/3cada74087687907311b52781354ff551e10a0ed/>

*** Diff to previous build ***
============================
PASS -> KFAIL: gdb.threads/process-dies-while-handling-bp.exp: non_stop=on: cond_bp_target=1: inferior 1 exited
============================


*** Complete list of XFAILs for this builder ***

To obtain the list of XFAIL tests for this builder, go to:

        <http://git.sergiodj.net/?p=gdb-xfails.git;a=blob;f=xfails/Ubuntu-AArch32-native-gdbserver-m32/xfails/master/xfail;hb=>

You can also see a pretty-printed version of the list, with more information
about each XFAIL, by going to:

        <http://git.sergiodj.net/?p=gdb-xfails.git;a=blob;f=xfails/Ubuntu-AArch32-native-gdbserver-m32/xfails/master/xfail.table;hb=>