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From: Luis Machado <>
To: Simon Marchi <>,
	Torbjorn SVENSSON <>,
Cc:, Yvan Roux <>
Subject: Re: [PATCH v3 1/2] gdb: dwarf2 generic implementation for caching function data
Date: Fri, 20 Jan 2023 17:33:32 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 1/20/23 17:28, Simon Marchi wrote:
>> I suppose a generic cache might be useful in the long run, but it
>> would have an impact on other code paths and I'm not comfortable of
>> doing this major change now. Doing this change would imply that almost
>> everything related to unwinding is impacted in one way or another and
>> I suppose we would need to test that. With the solution I proposed,
>> only Arm Cortex would be impacted and the scope for testing would be
>> rather small.
> I understand the feeling.  It's impossible to test every change on every
> configuration.  We do our best to understand the code and how the change
> will impact different configurations, but we also have to accept a
> certain level of risk that we will break something, otherwise we will
> never change / improve anything.  More eyes on the code, more people
> testing regularly with different configurations and more configurations
> on the Buildbot can help mitigate that.
>> I'm also aiming to resolve this for GDB13, so doing this major change
>> is a bit late in the sprint, right?
> Indeed.  Then I think it's fine to introduce what you have, and then we
> could replace it with a more general solution later.
>> If you have a better idea on how to cache everything, like in your 3
>> ideas above, please don't hesitate do share the implementation. :)
> I imagine something simple.  A hash table in frame_info or somewhere
> else, where frame_unwind_register_value would put values returned by
> `next_frame->unwind->prev_register`, which would be returned directly on
> subsequent calls.  This makes the assumption that a given frame info
> object has the same unwinder throughout its lifetime, and that it will
> return the same register value throughout its lifetime.  I don't know of
> any situation where that is not true.
> To keep the allocation / deallocation cost down, the hash tables could
> be allocated on the frame obstack.

Maybe not a solution for now, but can't we use something like the trad-frame structs to cache
values/locations of registers for a given frame?

  reply	other threads:[~2023-01-20 17:33 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-19 10:29 Torbjörn SVENSSON
2023-01-19 10:29 ` [PATCH v3 2/2] gdb/arm: Use new dwarf2 function cache Torbjörn SVENSSON
2023-01-25 16:55   ` Luis Machado
2023-01-25 17:12     ` Simon Marchi
2023-01-25 20:15       ` Torbjorn SVENSSON
2023-01-19 16:53 ` [PATCH v3 1/2] gdb: dwarf2 generic implementation for caching function data Simon Marchi
2023-01-20 14:12   ` Torbjorn SVENSSON
2023-01-20 17:28     ` Simon Marchi
2023-01-20 17:33       ` Luis Machado [this message]
2023-01-20 17:43         ` Simon Marchi
2023-01-25  9:34           ` Torbjorn SVENSSON
2023-01-20 19:59 ` Tom Tromey
2023-01-25  9:39   ` Torbjorn SVENSSON
2023-01-25 16:11     ` Tom Tromey

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