Re: drivers/gpu/drm/i915/i915.prelink.o: warning: objtool: __intel_wait_for_register_fw.cold()+0xce: relocation to !ENDBR: vlv_allow_gt_wake.cold+0x0

Josh Poimboeuf
2022-04-06T18:01:48Z

On Wed, Apr 06, 2022 at 09:43:30AM +0200, Peter Zijlstra wrote:
> On Tue, Apr 05, 2022 at 10:32:51PM -0700, Josh Poimboeuf wrote:
> > More broadly, this issue could theoretically happen in some other places
> > throughout the kernel tree, since _THIS_IP_ is fundamentally unreliable
> > as currently written.
> >
> > So we could look at making _THIS_IP_ more predictable.
> >
> > Inline asm would work better ("lea 0(%rip), %[rip]"), but then you need
> > an arch-dependent implementation...
>
> Well, there's a ton of _THIS_IP_ instances all around, and it would be
> unfortunate to have them grow into actual code :/

What do you mean by growing into actual code? It's still just a single
instruction, as was the immediate load before.

Though, you pasted this on irc:

#define _THIS_IP_ ({ __label__ __here; __here: asm_volatile_goto ("":::: __here); (unsigned long)&&__here; })

which seems decent to me, though less than ideal because it grows an
ENDBR. But I like its arch-independence, so yeah, LGTM.

--
Josh