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Re: lib/55719 (Unwind tables for signal trampoline on amd64 are incorrect)

Ok, I've combined the two approaches like so:

The new patch continues to work for gccgo and does so with far less
complexity. I'm quite hopeful that this is now in a mergeable state.

On Sun, Oct 11, 2020 at 11:30 PM Nikhil Benesch
<> wrote:
> On Sun, Oct 11, 2020 at 10:35 PM Andrew Cagney <> wrote:
> > So any code wanting the caller's stack pointer will need to parse the
> > CFI and then unwind the stack-pointer (CFA is a convenient fiction
> > invented by DWARF).
> >
> > The only real expectation is that the CFA is constant through out the
> > lifetime of the frame (one of the things identifying  a single-stepped
> > call/return instruction is the changed CFA).
> Hmm, ok, so perhaps just picking a different CFA for this frame is
> acceptable then. My assertion that the CFA must be equal to RSP on
> amd64 is based only on this blog post [0], which is hardly
> authoritative.
> Kamil's patch as written sets the CFA to both R15 and later (RSP + 8),
> but that is easy enough to fix to drop the second .cfi_def_cfa
> directive. There is still the issue of generating the FDE one PC
> earlier than the beginning of the sigtramp symbol, but maybe I can
> work something out.
> Also apologies that my last mail was sent in HTML, not plain text.
> That should be fixed now.
> [0]:

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