From: Pedro Alves <pedro@palves.net>
To: Thiago Jung Bauermann <thiago.bauermann@linaro.org>,
Luis Machado <luis.machado@arm.com>
Cc: Simon Marchi <simark@simark.ca>,
Andrew Burgess <aburgess@redhat.com>,
Thiago Jung Bauermann via Gdb-patches
<gdb-patches@sourceware.org>
Subject: Re: [PATCH v3 4/8] gdbserver/linux-aarch64: When thread stops, update its target description
Date: Mon, 6 Feb 2023 20:26:32 +0000 [thread overview]
Message-ID: <3f4e3603-59e3-a896-72e4-d692646c4e44@palves.net> (raw)
In-Reply-To: <87y1pgaib6.fsf@linaro.org>
On 2023-02-02 2:54 a.m., Thiago Jung Bauermann via Gdb-patches wrote:
>
> Luis Machado <luis.machado@arm.com> writes:
>
>> On 2/1/23 16:21, Simon Marchi wrote:
>>>
>>>>> diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
>>>>> index 221de85aa2ee..b52eb23cc444 100644
>>>>> --- a/gdbserver/linux-low.h
>>>>> +++ b/gdbserver/linux-low.h
>>>>> @@ -604,6 +604,12 @@ class linux_process_target : public process_stratum_target
>>>>> /* Architecture-specific setup for the current thread. */
>>>>> virtual void low_arch_setup () = 0;
>>>>> + /* Allows arch-specific code to set the thread's target description when the
>>>>> + inferior stops. Returns nullptr if no thread-specific target description
>>>>> + is necessary. */
>>>>> + virtual const struct target_desc *
>>>>> + get_thread_tdesc (const thread_info *thread);
>>>>
>>>> I think the comment for this function is not correct. The function does
>>>> not SET the thread's target description, but just GETS a target
>>>> description suitable for `thread`. It's the caller's job to do the
>>>> setting.
>>> This comment also gave me pause. How does a getter set something. I
>>> then understood that it allowed the arch-specific code to provide a
>>> thread-specific tdesc. I would suggest just:
>>
>> FWIW, I read it as "the functions *allows* arch-specific code to set".
>> So it doesn't set on its own, but it does allow something else to do
>> it.
>
> Yes, that's what was in my mind when I wrote the comment. But I agree
> it's unclear, and I adopted Simon's suggested version.
>
>>> The other thought I had while re-reading the patch is why do we need to
>>> return and store nullptr if the thread target description is the same as
>>> the main one for the process. get_thread_tdesc could just return
>>> process_info->tdesc if we don't need a separate tdesc, and we would
>>> store that same pointer in thread_info->tdesc.
>
> We don't need to return and store nullptr if the thread target
> description is the same as the main one for the process. Things will
> work fine if we do as you suggest. IIRC my private branch worked liked
> that for a while, before I changed it to the current version.
>
> I changed it because I thought it was a clearer mental model if
> thread_info->tdesc is nullptr when there's not thread-specific target
> description. I can make the get_thread_tdesc method always return a
> valid target description if you think it's better that way.
>
>>> And get_thread_tdesc would just return that (in fact,
>>> get_thread_tdesc might not be necessary then). Perhaps it makes some
>>> things more complicated down the road, but I can't think of anything.
>
> Sorry, I don't understand this part. get_thread_tdesc is necessary
> because it's the hook that allows arch-specific code to provide a target
> description for the thread. I don't see how it can become unnecessary.
>
> Perhaps you mean the get_thread_target_desc function? Sorry about the
> names being so similar, I spent some time trying to think of a better
> name for either the method or the function but failed.
Please drop the "get_" prefix from the class method, it doesn't really
add value, and we typically don't add it. Most GDB getter/setters are
in foo() / set_foo() pair style, rather than get_foo() / set_foo().
A "get_" prefix is however typically used for global getter functions.
FWIW, I have the same thought as Simon while reading this.
>
> In any case, it wouldn't be possible to make get_thread_target_desc just
> return thread_info->tdesc because at least the way these patches are
> currently written, when the inferior starts or a new thread of the
> inferior is spawned thread_info->tdesc is nullptr. gdbserver will only
> call get_thread_tdesc after the first stop (in get_thread_regcache, in
> the process of obtaining the pc register), so we will need to cope with
> that situation.
>
>> Sounds reasonable.
>>
>> Moving towards thread-specific target descriptions/gdbarch would be a positive thing given
>> the SVE precedent. The process-wide target description/gdbarch no
>> longer reflects the correct settings for each thread on AArch64's with SVE support.
>
> In the first version of these patches I removed the process-wide target
> description and moved it to thread_info, but it was a big patch that
> touched many targets. I can bring it back if you think it's worth it.
>
>
next prev parent reply other threads:[~2023-02-06 20:26 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 [this message]
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
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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