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From: Luis Machado <luis.machado@arm.com>
To: Joel Brobecker <brobecker@adacore.com>,
	Torbjorn SVENSSON <torbjorn.svensson@foss.st.com>,
	simon.marchi@polymtl.ca, tom@tromey.com
Cc: gdb-patches@sourceware.org
Subject: Re: GDB 13 release -- 2023-01-21 Update
Date: Fri, 27 Jan 2023 06:38:52 +0000	[thread overview]
Message-ID: <47dff98e-b714-2d72-bc3b-c14c4e0313d0@arm.com> (raw)
In-Reply-To: <Y9NvgBUvtCBfp0Qi@adacore.com>

On 1/27/23 06:30, Joel Brobecker wrote:
> Hello,
> 
>>>     * [Torbjorn] tdep/29738
>>>       Arm M-profile dwarf2 unwinder performance suffers from exponential growth
>>>       https://sourceware.org/bugzilla/show_bug.cgi?id=29738
>>>
>>>       patch v3, 2023-01-19, reviewed 2023-01-20:
>>>       https://sourceware.org/pipermail/gdb-patches/2023-January/195915.html
>>
>> I just pushed this for master.
>> Is it okay to also push the 2 patches to gdb-13-branch?
> 
> For the avoidance of doubt, my understanding is that we are talking
> about the following two patches:
> 
>      commit d72ba177c85f2ad18d0dcabdd8844532c9acb819
>      Author: Torbj�rn SVENSSON <torbjorn.svensson@foss.st.com>
>      Date:   Thu Nov 17 12:17:53 2022 +0100
>      Subject: gdb: dwarf2 generic implementation for caching function data
> 
> ... and ...
> 
>      commit 5cf11483141a58314834653003e49709b47822d5
>      Author: Torbj�rn SVENSSON <torbjorn.svensson@foss.st.com>
>      Date:   Thu Nov 17 12:18:20 2022 +0100
>      Subject: gdb/arm: Use new dwarf2 function cache
> 
> I hope I having missed any other patch!
> 
> The first one adds, as the subject indicates, a framework for
> caching frame-related information, and the second patch takes
> advantage of that framework,
> 
> Luis marked the corresponding PR as "important to fix", so
> I'm assuming the impact if we do not backport is significant
> (exponentional performance degradation). I was confused into
> thinking that this would "only" impact Cortex-m without security
> extensions, but maybe it's the opposite actually.

It affects m-profiles, but it affects the targets with the security extensions more, as they have more SP registers.

> 
> So the next question is, what is the potential impact if we
> backport the patch and there is a bug in it:
> 
>    - Well, it touches the generic Arm unwinding code, so
>      worse case scenario, DWARF-based unwinding is broken?

The change is restricted to m-profiles. Unless there is something really off with the caching code, it should break all Arm unwinding.

> 
>    - With that said, the patch appears to simply add a cache,
>      so the logic of it all doesn't appear to be extremely
>      complicated. So I would rate the risk to be low.

That's what it seems to me.

I think another round of testing would be a good step to make sure there are no hidden bugs.

> 
> If Tom and/or Simon agree, my assessment is that it is fine
> to backport those two patches onto the gdb-13 branch.
> 


  reply	other threads:[~2023-01-27  6:39 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-21  6:08 Joel Brobecker
2023-01-25 20:18 ` Torbjorn SVENSSON
2023-01-27  6:30   ` Joel Brobecker
2023-01-27  6:38     ` Luis Machado [this message]
2023-01-27 17:17       ` Simon Marchi
2023-01-28  8:39         ` Luis Machado
2023-01-29 11:52           ` Joel Brobecker
2023-01-30 11:23             ` Luis Machado
2023-01-31  7:03               ` Joel Brobecker
2023-01-31 13:57                 ` Luis Machado
2023-01-31 14:33                   ` Luis Machado
2023-02-02  3:44                   ` Joel Brobecker

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