Re: [PATCH] x86: work around clang IAS bug referencing __force_order

[Linus Torvalds]

On Sat, Aug 22, 2020 at 11:17 AM Miguel Ojeda
<miguel.ojeda.sandonis@xxxxxxxxx> wrote:
>
> However, the important question is whether those users/companies care
> about running the latest kernels. Many of those definitely do not want
> to touch their kernel either. For those that do, there are several
> longterms to pick from that still support 4.9, as well as other
> workarounds.
>
> Thus I am usually in favor of raising the minimum whenever new hacks
> are required to be added. On the other hand, we already raised the
> version twice this year and it is not clear to me what is the minimum
> version we would need to go for to ensure this does not bite us.

Yeah. The good news is that I haven't seen a lot of pushback on the
gcc version updates so far. I was expecting some complaints. I haven't
seen a single one.

That may be because people did end up finding it very onerous and
complained internally on channels I haven't seen, but it might also be
indicative of us having perhaps been a bit too timid about compiler
version updates.

However, in this case, can we just leave that old "__force_order" hack
alone, and to work around the clang thing, just make a dummy
definition of it anyway.

Alternatively, just use the memory clobber. We use memory clobbers
elsewhere in inline asms to make sure they are serialized, it's not
normally a huge problem. Both clang and gcc should be smart enough to
know that a memory clobber doesn't matter for things like local
variables etc that might be on stack but have never had their address
taken.

Or are there other cases than that particular __force_order thing that
people now worry about?

             Linus