From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: alexandre.chartre@oracle.com, linux-kernel@vger.kernel.org,
jthierry@redhat.com, tglx@linutronix.de, x86@kernel.org,
mbenes@suse.cz
Subject: Re: [PATCH 8/8] x86/retpoline: Fix retpoline unwind
Date: Tue, 28 Apr 2020 20:30:28 +0200 [thread overview]
Message-ID: <20200428183028.GB13575@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200424193028.tecqlugzzue2n5vj@treble>
On Fri, Apr 24, 2020 at 02:30:28PM -0500, Josh Poimboeuf wrote:
> On Thu, Apr 23, 2020 at 02:47:25PM +0200, Peter Zijlstra wrote:
> > .macro CALL_NOSPEC reg:req
> > #ifdef CONFIG_RETPOLINE
> > - ANNOTATE_NOSPEC_ALTERNATIVE
> > - ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg),\
> > - __stringify(RETPOLINE_CALL %\reg), X86_FEATURE_RETPOLINE,\
> > - __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_AMD
> > + /*
> > + * This cannot be ALTERNATIVE_2 like with JMP_NOSPEC, because ORC
> > + * unwind data is alternative invariant and needs stack modifying
> > + * instructions to be in the same place for all alternatives.
> > + *
> > + * IOW the CALL instruction must be at the same offset for all cases.
> > + */
> > + ALTERNATIVE "", "lfence", X86_FEATURE_RETPOLINE_AMD
> > + ALTERNATIVE __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \
> > + __stringify(call __x86_retpoline_\reg), X86_FEATURE_RETPOLINE
>
> I'm missing why ALTERNATIVE_2 wouldn't work here. How is the call a
> "stack modifying instruction"? It's not an intra-function call so it
> shouldn't affect ORC at all, right?
My bad. I find it hard not to consider CALL a stack modification. Let me
fix that.
prev parent reply other threads:[~2020-04-28 18:31 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-23 12:47 [PATCH 0/8] objtool vs retpoline Peter Zijlstra
2020-04-23 12:47 ` [PATCH 1/8] objtool: is_fentry_call() crashes if call has no destination Peter Zijlstra
2020-04-23 12:47 ` [PATCH 2/8] objtool: UNWIND_HINT_RET_OFFSET should not check registers Peter Zijlstra
2020-04-23 12:47 ` [PATCH 3/8] objtool: Rework allocating stack_ops on decode Peter Zijlstra
2020-04-23 15:40 ` Alexandre Chartre
2020-04-23 15:54 ` Peter Zijlstra
2020-04-24 7:06 ` Alexandre Chartre
2020-04-23 16:16 ` Peter Zijlstra
2020-04-24 9:43 ` Miroslav Benes
2020-04-23 12:47 ` [PATCH 4/8] objtool: Add support for intra-function calls Peter Zijlstra
2020-04-23 14:34 ` Miroslav Benes
2020-04-23 15:22 ` Peter Zijlstra
2020-04-24 9:37 ` Miroslav Benes
2020-04-24 14:07 ` Miroslav Benes
2020-04-23 12:47 ` [PATCH 5/8] x86/speculation: Change FILL_RETURN_BUFFER to work with objtool Peter Zijlstra
2020-04-23 15:45 ` Alexandre Chartre
2020-04-24 19:04 ` Josh Poimboeuf
2020-04-23 12:47 ` [PATCH 6/8] x86: Simplify retpoline declaration Peter Zijlstra
2020-04-24 19:09 ` Josh Poimboeuf
2020-04-23 12:47 ` [PATCH 7/8] x86: Change {JMP,CALL}_NOSPEC argument Peter Zijlstra
2020-04-23 12:47 ` [PATCH 8/8] x86/retpoline: Fix retpoline unwind Peter Zijlstra
2020-04-23 12:59 ` Peter Zijlstra
2020-04-24 19:30 ` Josh Poimboeuf
2020-04-28 18:30 ` Peter Zijlstra [this message]
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