linux-kernel - Re: [PATCH] ARM: module: Teach unwinder about PLTs

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Date:   Thu, 7 Jul 2022 08:34:09 +0200
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Kursad Oney <kursad.oney@...adcom.com>,
        Russell King <linux@...linux.org.uk>,
        Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: module: Teach unwinder about PLTs

Hello Florian,

On 06/07/2022 20:09, Florian Fainelli wrote:
>>
>> "unwind: Index not found eef26358" warnings keep popping up on
>> CONFIG_ARM_MODULE_PLTS-enabled systems if the PC points to a PLT veneer.
>> Teach the unwinder how to deal with them, taking into account they don't
>> change state of the stack or register file except loading PC.
>>
>> Tested-by: Kursad Oney <kursad.oney@...adcom.com>
>> Link: https://lore.kernel.org/linux-arm-kernel/20200402153845.30985-1-kursad.oney@broadcom.com/
>> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>
> 
> I would be inclined to slap a Fixes tag to this patch so we get it back ported where appropriate, however it is not clear to me which specific
> commit(s) we should be listing here.

usually I don't hesitate to add "Fixes:" tag and this patch definitely could be ported to some
stable versions, but it's hard to say what it fixes. It's actually a combination of rarely
(if at all) used ARM_MODULE_PLTS functionality and other *debug* features, where unwinder is
used. In very similar case of commit 79f32b221b18c15a98507b101ef4beb52444cc6f
("ARM: 9079/1: ftrace: Add MODULE_PLTS support") I wasn't able to figure out which commit
I'm fixing.

I expect those who use ARM_MODULE_PLT and any kind of debugging to be able to backport the
patch downstream ;) 

-- 
Best regards,
Alexander Sverdlin.