x86: clear %db registers in new process

[kib]

Summary

Reported by: Michał Górny <[e-mail]>
PR: 254661

[kib]

Clearing %db registers seems to be the right thing to do for forked process.

What is the opinion about new thread? Should we inherit or clear db state? [Patch currently clears]

[mgorny_gentoo.org]

In D29496#661038, @kib wrote:

Clearing %db registers seems to be the right thing to do for forked process.

What is the opinion about new thread? Should we inherit or clear db state? [Patch currently clears]

I don't have a strong opinion. Because of the other bug I've reported earlier, in LLDB we have to copy them anyway, so clearing is fine for me.

That said, I haven't tested other arches, they may be affected as well.

[emaste]

In D29496#661056, @mgorny_gentoo.org wrote:

In D29496#661038, @kib wrote:

Clearing %db registers seems to be the right thing to do for forked process.

What is the opinion about new thread? Should we inherit or clear db state? [Patch currently clears]

I don't have a strong opinion.

Do you know what Linux does?

[mgorny_gentoo.org]

In D29496#661068, @emaste wrote:

Do you know what Linux does?

I don't know for sure but I haven't seen any dbreg copying code in the Linux plugin, so I think threads inherit dbregs on Linux.

[kib]

Only clear %dbX for new process, keep new thread inherit them.

[emaste]

LGTM. We can switch back to the per-thread case if we get new information.