Re: [PATCH] x86: bring back rep movsq for user access on CPUs without ERMS

[Linus Torvalds]

On Mon, 28 Aug 2023 at 11:04, Mateusz Guzik <mjguzik@xxxxxxxxx> wrote:
>
> Other files do it (e.g., see __copy_user_nocache), but I have no
> strong opinion myself.

So the __copy_user_nocache() thing is a case of that second issue -
see my comment about "some sane visually sensible grouping" of the
numbers.

Look closer, and you'll notice that they aren't actually sequential.
They are of the form XY where the X is the grouping, and Y is the
local number within that grouping.

That case also comes with a fair amount of comments about each group
for the extable entries.

But yes, we also do have a number of thos e"sequential labels". See
for example arch/x86/lib/getuser.S, where we then end up having all
the exception handling at the end because it is mostly shared across
cases. It's ugly.

We also have a lot of ugly cases that probably shouldn't use numbers
at all, eg csum_partial(). I think that goes back to some darker age
when things like "assembly is so trivial that it doesn't need any
fancy explanatory labels for code" was ok.

See also arch/x86/lib/memmove_64.S for similar horrors. I wonder if it
is a case of "use compiler to get almost the right code, then massage
things manually". Nasty, nasty. That should use legible names, not
random numbers.

I also suspect some people really thought that the numbers need to be
unique, and just didn't know to use local numbering.

             Linus