Re: Segfault in jit tuple deforming on arm64 due to LLVM issue

On Wed, Aug 28, 2024 at 12:07 AM Anthonin Bonnefoy
<anthonin(dot)bonnefoy(at)datadoghq(dot)com> wrote:
> On Tue, Aug 27, 2024 at 12:01 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> > Thanks! And that's great news. Do you want to report this experience
> > to the PR, in support of committing it? That'd make it seem easier to
> > consider shipping a back-ported copy...
>
> Yes, I will do that.

Thanks. Here's a slightly tidied up version:

1. I used namespace llvm::backport, instead of a different class
name. That minimises the diff against their code.

2. I tested against LLVM 10-18, and found that 10 and 11 lack some
needed symbols. So I just hid this code from them. Even though our
stable branches support those and even older versions, I am not sure
if it's worth trying to do something about that for EOL'd distros that
no one has ever complained about. I am willing to try harder if
someone thinks that's important...

One little problem I am aware of is that if you make an empty .o,
macOS's new linker issues a warning, but I think I could live with
that. I guess I could put a dummy symbol in there... FWIW those old
LLVM versions spit out tons of other warnings from the headers on
newer compilers too, so *shrug*, don't use them? But then if this
code lands in LLVM 19 we'll also be hiding it for 19+ too.

Next, I think we should wait to see if the LLVM project commits that
PR, this so that we can sync with their 19.x stable branch, instead of
using code from a PR. Our next minor release is in November, so we
have some time. If they don't commit it, we can consider it anyway: I
mean, it's crashing all over the place in production, and we see that
other projects are shipping this code already.