Re: [RFC PATCH 00/17] objtool: add base support for arm64

[Ard Biesheuvel <ardb@kernel.org>]

On Fri, 22 Jan 2021 at 18:44, Mark Brown <broonie@kernel.org> wrote:
>
> On Thu, Jan 21, 2021 at 12:54:52PM -0600, Josh Poimboeuf wrote:
>
> > 2) The shadow stack idea sounds promising -- how hard would it be to
> >    make a prototype reliable unwinder?
>
> In theory it doesn't look too hard and I can't see a particular reason
> not to try doing this - there's going to be edge cases but hopefully for
> reliable stack trace they're all in areas where we would be happy to
> just decide the stack isn't reliable anyway, things like nesting which
> allocates separate shadow stacks for each nested level for example.
> I'll take a look.

This reminds me - a while ago, I had a stab at writing a rudimentary
GCC plugin that pushes/pops return addresses to a shadow call stack
pointed to by x18 [0]
I am by no means suggesting that we should rely on a GCC plugin for
this, only that it does seem rather straight-forward for the compiler
to manage a stack with return addresses like that (although the devil
is probably in the details, as usual)

[0] https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=arm64-scs-gcc