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From: Florian Weimer <fweimer@redhat.com>
To: systemtap <systemtap@sourceware.org>
Cc: Sergio Durigan Junior <sergiodj@sergiodj.net>,
	Luis Machado via Gdb <gdb@sourceware.org>,
	 Luis Machado via Libc-alpha <libc-alpha@sourceware.org>,
	 Luis Machado <luis.machado@linaro.org>,
	doko@debian.org
Subject: Re: GDB shared library tracking with stap probes x _dl_debug_state
Date: Sat, 08 May 2021 12:55:56 +0200	[thread overview]
Message-ID: <87tunda403.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <87bl9mi4xi.fsf@paluero> (Sergio Durigan Junior's message of "Fri, 07 May 2021 17:56:25 -0400")

* Sergio Durigan Junior:

> On Friday, May 07 2021, Luis Machado via Gdb wrote:
>
>> On 5/7/21 5:44 PM, Florian Weimer wrote:
>>> * Luis Machado via Libc-alpha:
>>> 
>>>> That's all fine, but there is one small detail that doesn't work for
>>>> armhf, and that is discovering if we're dealing with a PC that is arm
>>>> mode or thumb mode.
>>> Is it possible to recognize Arm mode vs thumb mode based on the NOP
>>> encoding at the probe address?
>>> 
>>
>> If we know the instruction is a NOP, it might be possible.
>
> I think it's guaranteed that the instruction is always going to be a
> NOP.

Maybe we can add a comment to that effect to the Systemtap sources?

Start of the thread is here:

  <https://sourceware.org/pipermail/gdb/2021-May/049421.html>

I think there are four distinct two-byte patterns at the probe
addressing, depending on endianess and thumb/non-thumb mode.  Looking at
the instruction has the clear advantage that it works with today's
binaries.

Thanks,
Florian


       reply	other threads:[~2021-05-08 10:55 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <b0b35028-2463-dd00-14af-22be2e7b6ff6@linaro.org>
     [not found] ` <878s4qb7fj.fsf@oldenburg.str.redhat.com>
     [not found]   ` <07b03137-a083-dada-68da-965779cd41ff@linaro.org>
     [not found]     ` <87bl9mi4xi.fsf@paluero>
2021-05-08 10:55       ` Florian Weimer [this message]
2021-05-10 14:16         ` Luis Machado
2021-05-11  8:00           ` Ulrich Weigand
2021-05-24 14:22           ` Luis Machado

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