linux-hardening - RE: [PATCH v2] ARM: unwind: improve unwinders for noreturn case

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Message-ID: <8f12147ee3cf4bbd8fc980821ae1deac@AcuMS.aculab.com>
Date: Fri, 22 Mar 2024 14:16:15 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Russell King' <linux@...linux.org.uk>
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Subject: RE: [PATCH v2] ARM: unwind: improve unwinders for noreturn case

...
> Whereas we already provide an abort() function because iirc the
> compiler used to emit branches to that due to noreturn functions. If
> correct, there's previous convention for doing this - and abort() is
> still exists in the kernel and in userspace since it's part of ANSI
> C. This would be a more reliable and portable solution, but probably
> not for embedded platforms - and that's probably why it got removed.

Wouldn't you want it to do a 'bl abort' so that you could do a backtrace
to find out which 'noreturn' function had returned?

But that leaves you with another 'noreturn' function that you have
difficulty generating a backtrace from.

So you'd need a compiler option to specify what to put there.
I'd suspect linux would like something that generates an 'undefined
instruction' trap - since that would be expected to fault with the
saved PC pointing to the instruction itself (but architectures may vary).

'One size' definitely doesn't 'fit all' :-)

	David

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