linux-kernel - Re: boot flooded with unwind: Index not found

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Date:   Wed, 9 Mar 2022 01:08:17 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Corentin Labbe <clabbe.montjoie@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: boot flooded with unwind: Index not found

On Wed, Mar 09, 2022 at 12:01:26AM +0000, Russell King (Oracle) wrote:
> To reinterate what I've just put on IRC - we have not got to the bottom
> of this problem yet - it still very much exists.
> 
> There seems to be something of a fundamental issue with the unwinder,
> it now appears to be going wrong and failing to unwind beyond a
> couple of functions, and the address it's coming out with appears to
> be incorrect. I've only just discovered this because I created my very
> own bug, and yet again, the timing sucks with the proximity of the
> merge window.
> 
> I'm getting:
> 
> [   13.198803] [<c0017728>] (unwind_backtrace) from [<c0012828>] (show_stack+0x10/0x14)
> [   13.198820] [<c0012828>] (show_stack) from [<c2be78d4>] (0xc2be78d4)
> 
> for the WARN_ON() stacktrace, and that address that apparently called
> show_stack() is most definitely rubbish and incorrect. This makes any
> WARN_ON() condition undebuggable.
> 
> This is with both 9183/1 and 9184/1 applied on top of pulling your
> "arm-ftrace-for-rmk" tag and also with just the "arm-vmap-stacks-v6"
> tag. This seems to point at one of these patches breaking the
> unwinder:
> 
> a1c510d0adc6 ARM: implement support for vmap'ed stacks
> 532319b9c418 ARM: unwind: disregard unwind info before stack frame is set up

The above commit appears to be what's breaking the unwinder. Without
this I get sane stacktraces. With it, the unwinder spits out stupid
function addresses.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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