From: Josh Stone <jistone@redhat.com>
To: Pedro Alves <palves@redhat.com>, gdb-patches@sourceware.org
Cc: philippe.waroquiers@skynet.be, sergiodj@redhat.com, eliz@gnu.org,
xdje42@gmail.com, scox@redhat.com
Subject: Re: [PATCH v4] Implement 'catch syscall' for gdbserver
Date: Tue, 12 Jan 2016 20:01:00 -0000 [thread overview]
Message-ID: <56955B84.7050905@redhat.com> (raw)
In-Reply-To: <56955283.1060502@redhat.com>
On 01/12/2016 11:22 AM, Pedro Alves wrote:
> On 01/12/2016 07:10 PM, Josh Stone wrote:
>> On 01/12/2016 04:05 AM, Pedro Alves wrote:
>>> On 01/09/2016 03:09 AM, Josh Stone wrote:
>>>
>>>>
>>>> 2016-01-08 Josh Stone <jistone@redhat.com>
>>>> Philippe Waroquiers <philippe.waroquiers@skynet.be>
>>>>
>>>> * gdb.texinfo (Remote Configuration): List the QCatchSyscalls packet.
>>>> (Stop Reply Packets): List the syscall entry and return stop reasons.
>>>> (General Query Packets): Describe QCatchSyscalls, and add it to the
>>>> table and detailed list of stub features.
>>>>
>>>
>>> "table of detailed", I think.
>>
>> I'm referring to two hunks:
>> - the table: Feature Name / Value Required / Default / Probe Allowed
>> - the list below it, "currently defined stub features, in more detail"
>>
>> Maybe I just need another article, "to the table and the detailed list"
>
> Ah. Yes, that way I think wouldn't have been confused.
>
>>
>>>> @@ -648,6 +658,12 @@ handle_extended_wait (struct lwp_info **orig_event_lwp, int wstat)
>>>> event_thr->last_resume_kind = resume_continue;
>>>> event_thr->last_status.kind = TARGET_WAITKIND_IGNORE;
>>>>
>>>> + /* Update syscall state in the new lwp, effectively mid-syscall too.
>>>> + The client really should send a new list to catch, in case the
>>>> + architecture changed, but for ANY_SYSCALL it doesn't matter. */
>>>> + event_lwp->syscall_state = TARGET_WAITKIND_SYSCALL_ENTRY;
>>>> + proc->syscalls_to_catch = syscalls_to_catch;
>>>
>>> The tone of this comment sounds to me as if the client should always
>>> send a new list, just in case, but for some odd reason it sometimes doesn't.
>>>
>>> I think we want to convey the opposite, like:
>>>
>>> /* Update syscall state in the new lwp, effectively mid-syscall too. */
>>> event_lwp->syscall_state = TARGET_WAITKIND_SYSCALL_ENTRY;
>>>
>>> /* Restore the list to catch. Don't rely on the client, which is free
>>> to avoid sending a new list when the architecture doesn't change.
>>> Also, for ANY_SYSCALL, the architecture doesn't really matter. */
>>> proc->syscalls_to_catch = syscalls_to_catch;
>>
>> Sure, I'll take your rewrite verbatim, if you don't mind.
>
> Certainly don't mind.
>
>
>>
>>>> static int
>>>> +linux_supports_catch_syscall (void)
>>>> +{
>>>> + return (the_low_target.get_syscall_trapinfo != NULL
>>>> + && linux_supports_tracesysgood());
>>>
>>> Space: "linux_supports_tracesysgood ()"
>>
>> OK
>>
>>>> +proc test_catch_syscall_execve {} {
>>>> + global gdb_prompt decimal
>>>> +
>>>> + with_test_prefix "execve" {
>>>> +
>>>> + # Tell the test program we want an execve.
>>>> + gdb_test_no_output "set do_execve = 1"
>>>> +
>>>> + # Check for entry/return across the execve, making sure that the
>>>> + # syscall_state isn't lost when turning into a new process.
>>>> + insert_catch_syscall_with_arg "execve"
>>>> + check_continue "execve"
>>>> +
>>>> + # Remotes that don't track exec may report the raw SIGTRAP for it.
>>>> + # If we use stepi now, we'll get a consistent trap for all targets.
>>>> + gdb_test "stepi" ".*" "step after execve"
>>>
>>> Why is it important to do this raw SIGTRAP handling? What happens if you don't
>>> do this? Won't those targets already FAIL the check_continue tests?
>>
>> Just in case, the context from Linux man ptrace:
>>
>> If the PTRACE_O_TRACEEXEC option is not in effect for the execing
>> tracee, and if the tracee was PTRACE_ATTACHed rather that
>> PTRACE_SEIZEd, the kernel delivers an extra SIGTRAP to the tracee
>> after execve(2) returns. This is an ordinary signal (similar to
>> one which can be generated by kill -TRAP), not a special kind of
>> ptrace-stop.
>>
>> Since that's a signal-stop *after* execve returns, the check_continue
>> will have succeeded already.
>
> Still can't see how that step would help -- check_continue does two
> "continue"s. So one would stop at the random SIGTRAP, and FAIL,
> and another would lose control of the inferior, probably running
> to end.
The first continue hits syscall_entry:execve. The second continue hits
syscall_return:execve. The second is the bug I fixed -- if it forgot
syscall_state across exec, the return was reported like another entry.
After that, there might be an impending SIGTRAP stop, depending on
whether PTRACE_O_TRACEEXEC is active. The step was a way of just
effecting a SIGTRAP for everyone, so it was easy to match.
>> The check_continue is really the only bit I care about for this test
>> anyway. The rest is just trying to finish the target process cleanly.
>> I was having trouble matching consistent output since plain remote was
>> getting that SIGTRAP, but extended-remote would use exec events and not
>> report anything extra. Adding the stepi made both stop the same way.
>>
>> This is moot now, since plain remotes are now tracking exec events too.
>> I developed this test just before that went in last month. :)
>> I just tried with that stepi commented out, and the test still passes on
>> local, remote, and extended-remote, so I'll remove it.
>
> OK, yes, let's drop it then. :-)
>
> Patch is OK with these changes, BTW.
Great! I'll make these final tweaks and push it out.
next prev parent reply other threads:[~2016-01-12 20:01 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-30 11:02 [PATCH] " Josh Stone
2015-10-30 13:26 ` Eli Zaretskii
2015-11-01 22:15 ` Doug Evans
2015-11-02 18:24 ` Josh Stone
2015-11-21 10:29 ` Philippe Waroquiers
2015-11-23 4:20 ` Doug Evans
2015-11-23 4:20 ` Doug Evans
2015-11-25 2:37 ` Josh Stone
2015-11-26 2:53 ` [PATCH v2 1/2] gdbserver: Set Linux ptrace options ASAP Josh Stone
2015-11-26 2:54 ` [PATCH v2 2/2] Implement 'catch syscall' for gdbserver Josh Stone
2015-11-26 10:34 ` [PATCH v2 1/2] gdbserver: Set Linux ptrace options ASAP Pedro Alves
2015-11-30 18:50 ` Josh Stone
2015-12-01 20:17 ` Josh Stone
2015-12-02 14:01 ` Pedro Alves
2015-12-04 2:26 ` [PATCH v3 1/2] gdbserver: set ptrace flags after creating inferiors Josh Stone
2015-12-04 2:27 ` [PATCH v3 2/2] Implement 'catch syscall' for gdbserver Josh Stone
2015-12-04 8:45 ` Eli Zaretskii
2015-12-05 2:14 ` Josh Stone
2015-12-05 8:02 ` Eli Zaretskii
2015-12-07 16:50 ` Josh Stone
2015-12-07 17:15 ` Eli Zaretskii
2015-12-04 13:18 ` Pedro Alves
2015-12-05 2:16 ` Josh Stone
2015-12-08 13:31 ` Pedro Alves
2015-12-08 19:02 ` Josh Stone
2015-12-08 13:37 ` Pedro Alves
2015-12-11 21:19 ` Josh Stone
2015-12-16 15:42 ` Pedro Alves
2016-01-09 3:09 ` [PATCH v4] " Josh Stone
2016-01-09 7:37 ` Eli Zaretskii
2016-01-11 17:44 ` Philippe Waroquiers
2016-01-12 12:05 ` Pedro Alves
2016-01-12 19:10 ` Josh Stone
2016-01-12 19:22 ` Pedro Alves
2016-01-12 20:01 ` Josh Stone [this message]
2016-03-29 14:27 ` Yao Qi
2016-03-29 18:12 ` Josh Stone
2016-03-29 23:49 ` Josh Stone
2016-03-30 12:23 ` Yao Qi
2016-03-31 1:10 ` Josh Stone
2016-04-01 13:05 ` Yao Qi
2016-04-01 16:38 ` Josh Stone
2016-05-29 16:47 ` [doc] NEWS: QCatchSyscalls: simplify Jan Kratochvil
2016-05-29 17:29 ` Eli Zaretskii
2016-05-29 17:50 ` Jan Kratochvil
2016-05-29 18:19 ` Eli Zaretskii
2016-05-29 18:47 ` [commit] " Jan Kratochvil
2015-12-04 12:16 ` [PATCH v3 1/2] gdbserver: set ptrace flags after creating inferiors Pedro Alves
2015-12-05 2:14 ` Josh Stone
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