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From: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
To: Simon Marchi <simark@simark.ca>
Cc: Andrew Burgess <aburgess@redhat.com>,
	Thiago Jung Bauermann via Gdb-patches
	<gdb-patches@sourceware.org>,
	Simon Marchi <simon.marchi@efficios.com>
Subject: Re: [PATCH v3 5/8] gdbserver: Transmit target description ID in thread list and stop reply
Date: Thu, 02 Feb 2023 21:43:58 +0000	[thread overview]
Message-ID: <87ilgjagkh.fsf@linaro.org> (raw)
In-Reply-To: <4ee73f43-ae93-ebf1-41ea-6cf68649fb2b@simark.ca>


Simon Marchi <simark@simark.ca> writes:

> On 2/1/23 07:07, Andrew Burgess via Gdb-patches wrote:
>> Additionally, I think it would be worth adding a new feature to the
>> qSupported packet, maybe 'per-thread-tdesc'.  With this added, GDB would
>> be able to tell gdbserver that it supports this feature, and gdbserver
>> will be able to confirm that the feature is supported.
>> 
>> I'm not 100% sure what we'd want to do if it turns out GDB doesn't
>> support the feature?  Is it better to push on with GDB using the wrong
>> target description?  Or would it be better if gdbserver exits with an
>> error suggesting the GDB needs updating?  In some ways, _what_ we do
>> doesn't really matter to me, but I think having the feature will allow
>> us to pick a suitable error handling solution later if needed.
>> 
>> I'd be happy if adding the feature was done as a separate patch in this
>> series, but I do think it should be part of this series.
>
> I forgot to comment on that part.  Just to think out loud:

I tested the two cases you mentioned below.

> - If GDB supports the new feature but GDBserver doesn't, I guess that
>   debugging works exactly like today?  What happens today if a remote
>   thread changes its SVE vector size, the registers that GDB shows will
>   simply not reflect the reality, they might have bogus values, but
>   debugging will otherwise work?

Yes, that's exactly what happens.

> - If GDB does not support the new feature but GDBserver does, I guess it
>   is problematic, because GDBserver will assume that GDB will have
>   adjusted its expectations about the length (and layout) of the g
>   packet response, since it told GDB about the thread-specific tdesc.
>   But since GDB doesn't know about thread-specific tdescs, it will try
>   to interpret the g packet response with the register layout of the
>   process-wide tdesc, possibly leading to the infamous "Remote 'g'
>   packet reply is too long", if the received response is longer than
>   expected.

This too.

> So, I agree that we need some feature flag for this.

Ok, I will add it for the next version of the patches.

-- 
Thiago

  reply	other threads:[~2023-02-02 21:44 UTC|newest]

Thread overview: 94+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-30  4:45 [PATCH v3 0/8] gdbserver improvements for AArch64 SVE support Thiago Jung Bauermann
2023-01-30  4:45 ` [PATCH v3 1/8] gdbserver: Add assert in find_register_by_number Thiago Jung Bauermann
2023-01-31 17:05   ` Simon Marchi
2023-01-31 19:49     ` Thiago Jung Bauermann
2023-02-01 15:43       ` Simon Marchi
2023-01-30  4:45 ` [PATCH v3 2/8] gdbserver: Add PID parameter to linux_get_auxv and linux_get_hwcap Thiago Jung Bauermann
2023-02-01  9:07   ` Luis Machado
2023-02-01 10:54   ` Andrew Burgess
2023-02-01 16:01     ` Simon Marchi
2023-02-01 19:33       ` Thiago Jung Bauermann
2023-02-01 19:53         ` Simon Marchi
2023-02-01 21:55           ` Thiago Jung Bauermann
2023-02-06 19:54   ` Pedro Alves
2023-02-06 20:16     ` Simon Marchi
2023-02-07 15:19       ` Pedro Alves
2023-02-07 21:47         ` Thiago Jung Bauermann
2023-02-09  1:31           ` Simon Marchi
2023-02-10  3:54             ` Thiago Jung Bauermann
2023-02-07 22:28     ` Thiago Jung Bauermann
2023-01-30  4:45 ` [PATCH v3 3/8] gdbserver/linux-aarch64: Factor out function to get aarch64_features Thiago Jung Bauermann
2023-02-01  8:59   ` Luis Machado
2023-02-01 16:04     ` Simon Marchi
2023-02-01 22:13       ` Thiago Jung Bauermann
2023-01-30  4:45 ` [PATCH v3 4/8] gdbserver/linux-aarch64: When thread stops, update its target description Thiago Jung Bauermann
2023-02-01  9:05   ` Luis Machado
2023-02-01 11:06   ` Andrew Burgess
2023-02-01 16:21     ` Simon Marchi
2023-02-01 16:32       ` Luis Machado
2023-02-02  2:54         ` Thiago Jung Bauermann
2023-02-02  3:47           ` Simon Marchi
2023-02-03  3:47             ` Thiago Jung Bauermann
2023-02-03 11:13               ` Luis Machado
2023-02-04 15:26                 ` Thiago Jung Bauermann
2023-02-03 11:11             ` Luis Machado
2023-02-04 15:21               ` Thiago Jung Bauermann
2023-02-06  9:07                 ` Luis Machado
2023-02-06 12:15                   ` Thiago Jung Bauermann
2023-02-06 20:29                 ` Pedro Alves
2023-02-07  8:11                   ` Luis Machado
2023-02-07 14:39                     ` Thiago Jung Bauermann
2023-02-03 10:57           ` Luis Machado
2023-02-04  6:18             ` Thiago Jung Bauermann
2023-02-06 20:26           ` Pedro Alves
2023-02-07 21:06             ` Thiago Jung Bauermann
2023-02-09  2:46               ` Simon Marchi
2023-02-10  3:29                 ` Thiago Jung Bauermann
2023-02-10 14:56                   ` Luis Machado
2023-02-10 15:04                     ` Tom Tromey
2023-02-10 15:28                       ` Luis Machado
2023-02-10 17:26                       ` Thiago Jung Bauermann
2023-02-10 21:01                         ` Simon Marchi
2023-01-30  4:45 ` [PATCH v3 5/8] gdbserver: Transmit target description ID in thread list and stop reply Thiago Jung Bauermann
2023-01-30 12:52   ` Eli Zaretskii
2023-01-30 14:05     ` Thiago Jung Bauermann
2023-02-01  9:39   ` Luis Machado
2023-02-01 12:07   ` Andrew Burgess
2023-02-01 13:03     ` Eli Zaretskii
2023-02-01 17:37     ` Simon Marchi
2023-02-02 20:36       ` Thiago Jung Bauermann
2023-02-02 20:56         ` Simon Marchi
2023-02-01 20:46     ` Simon Marchi
2023-02-02 21:43       ` Thiago Jung Bauermann [this message]
2023-02-01 14:51   ` Andrew Burgess
2023-02-01 17:03     ` Simon Marchi
2023-02-02 19:52       ` Thiago Jung Bauermann
2023-02-02 20:51         ` Simon Marchi
2023-02-03  2:44           ` Thiago Jung Bauermann
2023-02-03 16:29             ` Andrew Burgess
2023-02-04  6:08               ` Thiago Jung Bauermann
2023-02-03 11:22       ` Luis Machado
2023-02-03 12:50         ` Simon Marchi
2023-01-30  4:45 ` [PATCH v3 6/8] gdb/remote: Parse tdesc field in stop reply and threads list XML Thiago Jung Bauermann
2023-02-01  9:52   ` Luis Machado
2023-02-05  0:06     ` Thiago Jung Bauermann
2023-02-06  9:10       ` Luis Machado
2023-02-01 14:32   ` Andrew Burgess
2023-02-01 19:50     ` Simon Marchi
2023-02-01 20:16       ` Simon Marchi
2023-02-03 11:27         ` Luis Machado
2023-02-03 13:19           ` Simon Marchi
2023-02-03 16:33             ` Andrew Burgess
2023-01-30  4:45 ` [PATCH v3 7/8] gdb/aarch64: Detect vector length changes when debugging remotely Thiago Jung Bauermann
2023-02-01  9:58   ` Luis Machado
2023-02-01 15:26   ` Andrew Burgess
2023-02-01 20:20     ` Simon Marchi
2023-02-03 11:31       ` Luis Machado
2023-02-03 16:38       ` Andrew Burgess
2023-02-03 19:07         ` Simon Marchi
2023-01-30  4:45 ` [PATCH v3 8/8] gdb/testsuite: Add test to exercise multi-threaded AArch64 SVE inferiors Thiago Jung Bauermann
2023-02-01 10:10   ` Luis Machado
2023-02-06 19:11 ` [PATCH v3 0/8] gdbserver improvements for AArch64 SVE support Pedro Alves
2023-02-06 20:05   ` Simon Marchi
2023-02-06 21:06     ` Pedro Alves
2023-02-07 13:49       ` Simon Marchi

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