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SubjectRe: [PATCH v7 02/11] x86/retpoline: Temporarily disable objtool when CONFIG_RETPOLINE=y
On Tue, Jan 09, 2018 at 02:43:08PM +0000, David Woodhouse wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> objtool's assembler currently cannot deal with the code generated by the
> retpoline compiler and throws hundreds of warnings, mostly because it sees
> calls that don't have a symbolic target.
>
> Exclude all the options that rely on objtool when RETPOLINE is active.
>
> This mainly means that the kernel has to fallback to use the frame pointer
> unwinder and livepatch is not supported.
>
> Josh is looking into resolving the issue.

I have a fix brewing for this, in two parts:

- Part 1 will allow objtool to understand the flow *around* the
retpolines (but not *inside* them). Which basically means that ORC
will still get confused if it tries to unwind from inside a retpoline,
but otherwise it should work fine. This code is pretty much done,
just need to do some testing with it first. This should allow us to
re-enable objtool and friends: ORC, reliable stacks, livepatch
consistency model.

- Part 2 will add ORC annotations for inside the retpolines. This will
be a little harder, but I have my fingers crossed that it's do-able
within a week or so.

--
Josh

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