Re: [PATCH] gdbstub: Switch to the thread receiving a signal

[Pavel Labath]

Thanks for taking a look. I've sent out a new version of the patch. 
Besides the Makefile change, I have also replaced the direct 
gdbserver_state manipulation with a call to gdb_set_stop_cpu.

Further responses inline.

On 19/10/2021 19:02, Alex Bennée wrote:
> Pavel Labath <pavel@labath.sk> writes:
>
> > Respond with Txxthread:yyyy; instead of a plain Sxx to indicate which
> > thread received the signal. Otherwise, the debugger will associate it
> > with the main one. Also automatically select this thread, as that is
> > what gdb expects.
> >
> > Signed-off-by: Pavel Labath <pavel@labath.sk>
> > ---
> >   gdbstub.c                                     |  9 ++-
> >   tests/tcg/multiarch/Makefile.target           |  7 +++
> >   .../gdbstub/test-thread-breakpoint.py         | 60 +++++++++++++++++++
> >   3 files changed, 74 insertions(+), 2 deletions(-)
> >   create mode 100644 tests/tcg/multiarch/gdbstub/test-thread-breakpoint.py
> >
> > diff --git a/gdbstub.c b/gdbstub.c
> > index 36b85aa..7bd4479 100644
> > --- a/gdbstub.c
> > +++ b/gdbstub.c
> > @@ -3138,8 +3138,13 @@ gdb_handlesig(CPUState *cpu, int sig)
> >       tb_flush(cpu);
> >   
> >       if (sig != 0) {
> > -        snprintf(buf, sizeof(buf), "S%02x", target_signal_to_gdb(sig));
> > -        put_packet(buf);
> > +        gdbserver_state.c_cpu = cpu;
> > +        gdbserver_state.g_cpu = cpu;
> > +        g_string_printf(gdbserver_state.str_buf,
> > +                        "T%02xthread:", target_signal_to_gdb(sig));
> > +        gdb_append_thread_id(cpu, gdbserver_state.str_buf);
> > +        g_string_append_c(gdbserver_state.str_buf, ';');
> > +        put_strbuf();
> >       }
> >       /* put_packet() might have detected that the peer terminated the
> >          connection.  */
> > diff --git a/tests/tcg/multiarch/Makefile.target 
> > b/tests/tcg/multiarch/Makefile.target
> > index 85a6fb7..c7b7e8b 100644
> > --- a/tests/tcg/multiarch/Makefile.target
> > +++ b/tests/tcg/multiarch/Makefile.target
> > @@ -73,6 +73,13 @@ run-gdbstub-qxfer-auxv-read: sha1
> >                 --bin $< --test 
> > $(MULTIARCH_SRC)/gdbstub/test-qxfer-auxv-read.py, \
> >         "basic gdbstub qXfer:auxv:read support")
> >   
> > +run-gdbstub-thread-breakpoint: testthread
> > +       $(call run-test, $@, $(GDB_SCRIPT) \
> > +               --gdb $(HAVE_GDB_BIN) \
> > +               --qemu $(QEMU) --qargs "$(QEMU_OPTS)" \
> > +               --bin $< --test 
> > $(MULTIARCH_SRC)/gdbstub/test-thread-breakpoint.py, \
> > +       "hitting a breakpoint on non-main thread")
> > +
>
> You also need to add the test to EXTRA_RUNS here (or just bellow in fact).
Done.

> >   else
> >   run-gdbstub-%:
> >         $(call skip-test, "gdbstub test $*", "need working gdb")
> > diff --git a/tests/tcg/multiarch/gdbstub/test-thread-breakpoint.py 
> > b/tests/tcg/multiarch/gdbstub/test-thread-breakpoint.py
> > new file mode 100644
> > index 0000000..798d508
> > --- /dev/null
> > +++ b/tests/tcg/multiarch/gdbstub/test-thread-breakpoint.py
> > @@ -0,0 +1,60 @@
> > +from __future__ import print_function
> > +#
> > +# Test auxiliary vector is loaded via gdbstub
> > +#
> > +# This is launched via tests/guest-debug/run-test.py
> > +#
> > +
> > +import gdb
> > +import sys
> > +
> > +failcount = 0
> > +
> > +def report(cond, msg):
> > +    "Report success/fail of test"
> > +    if cond:
> > +        print ("PASS: %s" % (msg))
> > +    else:
> > +        print ("FAIL: %s" % (msg))
> > +        global failcount
> > +        failcount += 1
> > +
> > +def run_test():
> > +    "Run through the tests one by one"
> > +
> > +    sym, ok = gdb.lookup_symbol("thread1_func")
> > +    gdb.execute("b thread1_func")
> > +    gdb.execute("c")
> > +
> > +    frame = gdb.selected_frame()
> > +    report(str(frame.function()) == "thread1_func", "break @
> >   %s"%frame)
>
> Does this actually check the correct thread is reported?
It does it indirectly -- there is only one thread which can have 
thread1_func on the stack. If we do not report the correct thread, 
selected_frame() will point into the bowels of pthread_join, as that's 
where the main thread will be stuck at.
I don't know of a direct way to check for the reported thread. 
gdb.selected_thread().name would be more direct, but I am not sure we 
would be able to correctly set the thread name on all supported platforms.

> > +
> > +#
> > +# This runs as the script it sourced (via -x, via run-test.py)
> > +#
> > +try:
> > +    inferior = gdb.selected_inferior()
> > +    arch = inferior.architecture()
> > +    print("ATTACHED: %s" % arch.name())
> > +except (gdb.error, AttributeError):
> > +    print("SKIPPING (not connected)", file=sys.stderr)
> > +    exit(0)
> > +
> > +if gdb.parse_and_eval('$pc') == 0:
> > +    print("SKIP: PC not set")
> > +    exit(0)
> > +
> > +try:
> > +    # These are not very useful in scripts
> > +    gdb.execute("set pagination off")
> > +    gdb.execute("set confirm off")
> > +
> > +    # Run the actual tests
> > +    run_test()
> > +except (gdb.error):
> > +    print ("GDB Exception: %s" % (sys.exc_info()[0]))
> > +    failcount += 1
> > +    pass
> > +
> > +print("All tests complete: %d failures" % failcount)
> > +exit(failcount)