From: Matthew Wilcox <willy@infradead.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
Ingo Molnar <mingo@kernel.org>,
x86@kernel.org, masahiroy@kernel.org, michal.lkml@markovi.net,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [tip: objtool/core] jump_label, x86: Allow short NOPs
Date: Tue, 29 Jun 2021 21:00:57 +0100 [thread overview]
Message-ID: <YNt7+fRNOnorLsYW@casper.infradead.org> (raw)
In-Reply-To: <YKS2oX/PCfp4NQ8V@hirez.programming.kicks-ass.net>
So this got merged without the corresponding Kbuild update being merged,
and my kernel failed to boot. Bisect got as far as
$ git bisect good
Bisecting: 4 revisions left to test after this (roughly 2 steps)
[ab3257042c26d0cd44793c741e2f89bf38b21fe8] jump_label, x86: Allow short NOPs
before my sluggish memory remembered this thread from six weeks ago.
So if anybody else hits this, do a make clean.
On Wed, May 19, 2021 at 08:56:33AM +0200, Peter Zijlstra wrote:
> On Tue, May 18, 2021 at 07:44:11PM -0500, Josh Poimboeuf wrote:
>
> > I'm not exactly thrilled that objtool now has the power to easily brick
> > a system :-/ Is it really worth it?
>
> The way I look at it is that not running objtool is a bug either way,
> bricking a system is ofcourse a somewhat more drastic failure mode than
> missing ORC info for example, but neither are good.
>
> As to worth, about half the jump labels are shorter now, this reduces I$
> pressure on hot paths. Any little thing to offset the ever increasing
> bulk seems like a good thing to me. But yes, it would be nice if the
> assemblers wouldn't suck so bad and this wouldn't need objtool :/ But
> I've tried poking the tools guys and they don't really seem interested
> :-(
>
> Also, only dirty builds are affected here; clean builds (always
> recommended afaik, because dep trouble isn't unheard of) are fine.
>
> > Anyway, here's one way to fix it. Maybe Masahiro has a better idea.
>
> Thanks! lemme go read up on this magic :-)
next prev parent reply other threads:[~2021-06-29 20:01 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-06 19:33 [PATCH 00/13] jump_label: Yet another attempt at variable sized jump_labels Peter Zijlstra
2021-05-06 19:33 ` [PATCH 01/13] objtool: Rewrite hashtable sizing Peter Zijlstra
2021-05-12 10:41 ` Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-06-10 18:14 ` [PATCH 01/13] " Nathan Chancellor
2021-06-10 18:43 ` Peter Zijlstra
2021-06-10 18:54 ` Nathan Chancellor
2021-06-10 18:50 ` Sami Tolvanen
2021-06-10 19:33 ` Peter Zijlstra
2021-06-10 19:43 ` Sami Tolvanen
2021-06-10 20:59 ` Nathan Chancellor
2021-06-14 13:19 ` [tip: objtool/core] objtool: Improve reloc hash size guestimate tip-bot2 for Peter Zijlstra
2021-05-06 19:33 ` [PATCH 02/13] x86,objtool: Dont exclude arch/x86/realmode/ Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] x86, objtool: " tip-bot2 for Peter Zijlstra
2021-05-06 19:33 ` [PATCH 03/13] jump_label, x86: Strip ASM jump_label support Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-05-06 19:33 ` [PATCH 04/13] jump_label, x86: Factor out the __jump_table generation Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-05-06 19:33 ` [PATCH 05/13] jump_label, x86: Improve error when we fail expected text Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-05-06 19:33 ` [PATCH 06/13] jump_label, x86: Introduce jump_entry_size() Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-05-06 19:33 ` [PATCH 07/13] jump_label, x86: Add variable length patching support Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-05-13 14:16 ` [PATCH 07.5/13] jump_label,x86: Remove unused JUMP_LABEL_NOP_SIZE Peter Zijlstra
2021-05-14 7:01 ` [tip: objtool/core] jump_label/x86: " tip-bot2 for Peter Zijlstra
2021-05-06 19:34 ` [PATCH 08/13] jump_label: Free jump_entry::key bit1 for build use Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-05-06 19:34 ` [PATCH 09/13] jump_label,x86: Emit short JMP Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] jump_label, x86: " tip-bot2 for Peter Zijlstra
2021-05-06 19:34 ` [PATCH 10/13] objtool: Decode jump_entry::key addend Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-05-06 19:34 ` [PATCH 11/13] objtool: Rewrite jump_label instructions Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-05-06 19:34 ` [PATCH 12/13] objtool: Provide stats for jump_labels Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-05-13 14:15 ` [PATCH 12.5/13] objtool: Reflow handle_jump_alt() Peter Zijlstra
2021-05-06 19:34 ` [PATCH 13/13] jump_label,x86: Allow short NOPs Peter Zijlstra
2021-05-06 19:49 ` Peter Zijlstra
2021-05-12 13:19 ` [tip: objtool/core] jump_label, x86: " tip-bot2 for Peter Zijlstra
2021-05-18 19:50 ` Peter Zijlstra
2021-05-18 20:24 ` Peter Zijlstra
2021-05-19 0:44 ` Josh Poimboeuf
2021-05-19 6:56 ` Peter Zijlstra
2021-06-29 20:00 ` Matthew Wilcox [this message]
2021-06-29 20:35 ` Matthew Wilcox
2021-06-30 7:07 ` Peter Zijlstra
2021-06-30 7:38 ` Peter Zijlstra
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