Re: [GIT PULL] perf tools fixes for v7.0: 2nd batch

[Linus Torvalds]

On Mon, 23 Mar 2026 at 03:57, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
>
>       tools arch x86: Sync the msr-index.h copy with the kernel sources
>       tools headers UAPI: Sync linux/kvm.h with the kernel sources
>       tools headers UAPI: Sync x86's asm/kvm.h with the kernel sources
>       tools headers: Synchronize linux/build_bug.h with the kernel sources

So I think we need to come up with some solution to *not* do this all,
because honestly, it's getting hugely annoying.

And it's not annoying due to the unnecessary diffs per se, but because
this tool header sync then causes 'objtool' - which also uses some of
those headers - to be rebuilt, and then that causes *everything* to be
rebuilt.

Just because the perf tree decided it needed to sync headers for
unexplained reasons.

The docs say "this works surprisingly well". That *used* to be the
case. But with objtool also being affected, it really does *not* work
well at all.

And no, the tools cannot use the kernel headers directly. That
*really* didn't work well, and required synchronizing kernel changes
with tooling changes, and was just a pain.

So the "header copies" solved a real problem, but we need to figure
out something better.

And honestly, the "something better" may be to just remove the
mindless check for "headers aren't 100% sync".

Because 99% of the time nobody cares. This time, for example, the
header changes in question were comments and stuff that was inside a
__KERNEL__ guard.

So how about just at least as a first step trying to remove the
warning that is actively detrimental, and only do header syncs when
there is a *real* reason for them?

                 Linus