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From: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
To: 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: Sat, 04 Feb 2023 15:21:32 +0000	[thread overview]
Message-ID: <87leldmp6r.fsf@linaro.org> (raw)
In-Reply-To: <9d30751a-589b-eb95-09b1-61d083ad9730@arm.com>


Luis Machado <luis.machado@arm.com> writes:

> On 2/2/23 03:47, Simon Marchi wrote:
>> On 2/1/23 21:54, Thiago Jung Bauermann wrote:
>>> 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.
>> Ok.  Would it work if a new thread initially inherited the tdesc from
>> its process?
>> 
>
> It should be fine because the first time we fetch a process target
> description, it is eventually obtained from the first and only thread.
> So the SVE vector length should be correct.
>
> Any subsequent attempts to use the process' target description (the
> first one we obtained), after further stops, may end up using an
> incorrect description.
>
> I think this is handled correctly by the target architecture target
> hook though. But there are other places where this is potentially
> incorrect.
>
> For example...
>
> - When using gcore to dump a core file, GDB only dumps a single target
> description. While this might be correct for a target with a fixed
> target description or a AArch64 target that doesn't support SVE, it
> likely won't be correctly for one AArch64 target supporting SVE if its
> threads changed vector length mid-execution. Either we emit target
> description notes by thread, or we don't emit a target description
> note for those cases.
>
> - When loading the above/older gcore core files back, GDB will use a
> potentially incorrect target description. If we decide to emit
> per-thread target descriptions, it should be fine. Otherwise we may
> need to have a "thread architecture" hook for core files as well.
>
> - The remote has no concept of a thread architecture (Thiago is
> addressing this with this patch series).
>
> - AArch64 frames may have slightly different vg values, which means
> their gdbarches are different as well.
>
> Given the differences between two gdbarches are small, we mostly get
> away with it. But if there are further differences (different hooks,
> for example), I fear we may run into a situation where we use an
> incorrect gdbarch to call a particular hook.

Indeed, good points! Thank you for bringing them up. I can address core
file dumping/loading after this series.

Regarding frames with different vg values, it's important to be aware of
this discrepancy but IMHO it makes sense to work on it when it becomes
a problem...

-- 
Thiago

  reply	other threads:[~2023-02-04 15:21 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 [this message]
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
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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