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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	alexei.starovoitov@gmail.com, ndesaulniers@google.com
Subject: Re: [PATCH v2 08/14] x86/retpoline: Create a retpoline thunk array
Date: Wed, 20 Oct 2021 10:09:56 -0700	[thread overview]
Message-ID: <20211020170956.g67xcsvvdkuqg3qa@treble> (raw)
In-Reply-To: <f33b9c4e-08c1-f88d-4873-82050a944010@citrix.com>

On Wed, Oct 20, 2021 at 05:46:39PM +0100, Andrew Cooper wrote:
> On 20/10/2021 16:57, Josh Poimboeuf wrote:
> > On Wed, Oct 20, 2021 at 12:44:50PM +0200, Peter Zijlstra wrote:
> >> Stick all the retpolines in a single symbol and have the individual
> >> thunks as inner labels, this should guarantee thunk order and layout.
> > How so?
> >
> > Just wondering what the purpose of the array is.  It doesn't seem to be
> > referenced anywhere.
> 
> The array property is what makes:
> 
> > +	reg = (target - &__x86_indirect_thunk_rax) /
> > +	      (&__x86_indirect_thunk_rcx - &__x86_indirect_thunk_rax);
> 
> safe in the next path.

The thunks were already 32-byte aligned.  I don't see how slapping a few
unused symbols around them does anything.

-- 
Josh


  reply	other threads:[~2021-10-20 17:10 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-20 10:44 [PATCH v2 00/14] x86: Rewrite the retpoline rewrite logic Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 01/14] objtool: Tag retpoline thunk symbols Peter Zijlstra
2021-10-20 15:17   ` Josh Poimboeuf
2021-10-26  7:55     ` Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 02/14] objtool: Explicitly avoid self modifying code in .altinstr_replacement Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 03/14] objtool: Shrink struct instruction Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 04/14] objtool,x86: Replace alternatives with .retpoline_sites Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 05/14] x86/retpoline: Remove unused replacement symbols Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 06/14] x86/asm: Fix register order Peter Zijlstra
2021-10-22 19:27   ` David Laight
2021-10-25 14:09   ` Borislav Petkov
2021-10-20 10:44 ` [PATCH v2 07/14] x86/asm: Fixup odd GEN-for-each-reg.h usage Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 08/14] x86/retpoline: Create a retpoline thunk array Peter Zijlstra
2021-10-20 15:57   ` Josh Poimboeuf
2021-10-20 16:46     ` Andrew Cooper
2021-10-20 17:09       ` Josh Poimboeuf [this message]
2021-10-20 19:22         ` Peter Zijlstra
2021-10-20 19:43           ` Josh Poimboeuf
2021-10-20 19:34       ` Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 09/14] x86/alternative: Implement .retpoline_sites support Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 10/14] x86/alternative: Handle Jcc __x86_indirect_thunk_\reg Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 11/14] x86/alternative: Try inline spectre_v2=retpoline,amd Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 12/14] x86/alternative: Add debug prints to apply_retpolines() Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 13/14] x86,bugs: Unconditionally allow spectre_v2=retpoline,amd Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 14/14] bpf,x86: Respect X86_FEATURE_RETPOLINE* Peter Zijlstra
2021-10-20 11:09   ` Peter Zijlstra
2021-10-20 16:56     ` Josh Poimboeuf
2021-10-20 19:23       ` Peter Zijlstra
2021-10-21  0:05     ` Alexei Starovoitov
2021-10-21  8:47       ` Peter Zijlstra
2021-10-21 18:03         ` Alexei Starovoitov
2021-10-21 22:37           ` Peter Zijlstra
2021-10-21 23:24             ` Alexei Starovoitov
2021-10-21 23:38               ` Josh Poimboeuf
2021-10-21 23:42                 ` Alexei Starovoitov
2021-10-22 11:31                   ` Peter Zijlstra
2021-10-22 15:22                     ` Alexei Starovoitov
2021-10-25 13:44                       ` Maciej Fijalkowski
2021-10-25 12:42                         ` Peter Zijlstra
2021-10-21 23:51         ` Zvi Effron
2021-10-22  8:33           ` Peter Zijlstra
2021-10-22 21:06             ` Zvi Effron
2021-10-21  0:07   ` Alexei Starovoitov
2021-10-21  0:18     ` Josh Poimboeuf
2021-10-21  8:53       ` Peter Zijlstra

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