From: Andrew Burgess <aburgess@redhat.com>
To: Simon Marchi <simark@simark.ca>,
Luis Machado <luis.machado@arm.com>,
Thiago Jung Bauermann via Gdb-patches
<gdb-patches@sourceware.org>
Cc: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Subject: Re: [PATCH v3 6/8] gdb/remote: Parse tdesc field in stop reply and threads list XML
Date: Fri, 03 Feb 2023 16:33:44 +0000 [thread overview]
Message-ID: <87sffmr9nb.fsf@redhat.com> (raw)
In-Reply-To: <7ad8e78a-7966-a714-d4cb-ebe1bfa606ee@simark.ca>
Simon Marchi <simark@simark.ca> writes:
> On 2/3/23 06:27, Luis Machado wrote:
>> On 2/1/23 20:16, Simon Marchi via Gdb-patches wrote:
>>>> IIUC, the tdescs would be deleted during the
>>>> pop_all_targets_at_and_above, when the refcount of the remote_target
>>>> gets to 0 and it gets deleted. And the threads would be removed in
>>>> generic_mourn_inferior just after.
>>>>
>>>> An idea could be to call generic_mourn_inferior before
>>>> remote_unpush_target (no idea if it works). Another one would be to
>>>> get a temporary reference to the remote_target object in
>>>> remote_unpush_target, just so that it outlives the threads.
>>>> Or maybe we should say that it's a process target's responsibility to
>>>> delete any thread it "owns" before getting deleted itself.
>>>
>>> Another question related to this popped while reading the following
>>> patch. When creating a gdbarch from a tdesc, the gdbarch keeps a
>>> pointer to that tdesc (accessible through gdbarch_target_desc). And
>>> AFAIK, we never delete gdbarches. So I suppose the gdbarch will refer a
>>> stale target desc. At first I thought it wouldn't be a problem in
>>> practice, because while that gdbarch object still exists, nothing
>>> references it (it is effectively leaked). But then I remember that we
>>> cache gdbarches to avoid creating arches with duplicate features. So
>>> later (let's say if you connect again to a remote), we might want to
>>> create a gdbarch with the same features as before, and we'll dig up the
>>> old gdbarch, that points to the now deleted tdesc.
>>
>> The target descriptions for aarch64 are all cached using a map in gdb/aarch64-tdep.c:
>>
>> /* All possible aarch64 target descriptors. */
>> static std::unordered_map <aarch64_features, target_desc *> tdesc_aarch64_map;
>>
>> I don't think we should try to delete those, and they should live throughout the life of gdb (unless things get large, then we might consider cleanups).
>
> When debugging natively with GDB, that's true. When debugging remotely,
> on GDBserver-side, that's true too. But when debugging remotely, on
> GDB-side, don't we create a new target_desc object for each read target
> description?
>
> Ok, I just saw in xml-tdesc.c:
>
> /* A record of every XML description we have parsed. We never discard
> old descriptions, because we never discard gdbarches. As long as we
> have a gdbarch referencing this description, we want to have a copy
> of it here, so that if we parse the same XML document again we can
> return the same "struct target_desc *"; if they are not singletons,
> then we will create unnecessary duplicate gdbarches. See
> gdbarch_list_lookup_by_info. */
>
> static std::unordered_map<std::string, target_desc_up> xml_cache;
>
> So, at least, a remote sending the same exact XML over and over will
> lead to the same target_desc object being reused. And there won't be
> lifetime issues, since the target_desc created from XML also live
> forever. So I guess we're good.
Simon,
Thanks for chasing this down. I guess my concerns about object life
time are addressed then.
Thanks,
Andrew
next prev parent reply other threads:[~2023-02-03 16:33 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87sffmr9nb.fsf@redhat.com \
--to=aburgess@redhat.com \
--cc=gdb-patches@sourceware.org \
--cc=luis.machado@arm.com \
--cc=simark@simark.ca \
--cc=thiago.bauermann@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).