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From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: x86@kernel.org, jgross@suse.com, mbenes@suse.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 14/14] objtool,x86: Rewrite retpoline thunk calls
Date: Fri, 19 Mar 2021 16:56:30 +0100	[thread overview]
Message-ID: <YFTJro42GX6m7O5Q@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210319153026.cfqwyy36feqyunyd@treble>

On Fri, Mar 19, 2021 at 10:30:26AM -0500, Josh Poimboeuf wrote:
> On Fri, Mar 19, 2021 at 09:06:44AM +0100, Peter Zijlstra wrote:
> > > Also doesn't the alternative code already insert nops?
> > 
> > Problem is that the {call,jmp} *%\reg thing is not fixed length. They're
> > 2 or 3 bytes depending on which register is picked.
> 
> Why do they need to be fixed length?  Objtool can use sym->len as the
> alternative replacement length.  Then alternatives can add nops as
> needed.

UNDEF has size 0. That is, unless these symbols exist in the translation
unit (they do not) we have no clue.

Arguably I could parse the symbol name again and then we know the
register number and thus if we need REX etc.. but I figured we wanted to
avoid all that.

  reply	other threads:[~2021-03-19 15:57 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-18 17:11 [PATCH v2 00/14] x86,objtool: Optimize !RETPOLINE Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 01/14] x86: Add insn_decode_kernel() Peter Zijlstra
2021-03-19 10:40   ` Borislav Petkov
2021-03-18 17:11 ` [PATCH v2 02/14] x86/alternatives: Optimize optimize_nops() Peter Zijlstra
2021-03-21 12:06   ` Borislav Petkov
2021-03-22  8:17     ` Peter Zijlstra
2021-03-22 11:07       ` Borislav Petkov
2021-03-18 17:11 ` [PATCH v2 03/14] x86/retpoline: Simplify retpolines Peter Zijlstra
2021-03-19 17:18   ` David Laight
2021-03-22  9:32     ` Peter Zijlstra
2021-03-22 15:41       ` David Laight
2021-03-18 17:11 ` [PATCH v2 04/14] objtool: Correctly handle retpoline thunk calls Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 05/14] objtool: Per arch retpoline naming Peter Zijlstra
2021-03-19  2:38   ` Josh Poimboeuf
2021-03-19  9:07     ` Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 06/14] objtool: Fix static_call list generation Peter Zijlstra
2021-03-22 12:44   ` Miroslav Benes
2021-03-18 17:11 ` [PATCH v2 07/14] objtool: Rework rebuild_reloc logic Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 08/14] objtool: Add elf_create_reloc() helper Peter Zijlstra
2021-03-19  1:42   ` Josh Poimboeuf
2021-03-19  9:47     ` Peter Zijlstra
2021-03-19 15:12       ` Josh Poimboeuf
2021-03-19 15:24         ` Peter Zijlstra
2021-03-19 15:37           ` Josh Poimboeuf
2021-03-18 17:11 ` [PATCH v2 09/14] objtool: Extract elf_strtab_concat() Peter Zijlstra
2021-03-19  2:10   ` Josh Poimboeuf
2021-03-19  9:52     ` Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 10/14] objtool: Extract elf_symbol_add() Peter Zijlstra
2021-03-19  2:14   ` Josh Poimboeuf
2021-03-19  9:54     ` Peter Zijlstra
2021-03-19 15:04       ` Josh Poimboeuf
2021-03-18 17:11 ` [PATCH v2 11/14] objtool: Add elf_create_undef_symbol() Peter Zijlstra
2021-03-19  2:29   ` Josh Poimboeuf
2021-03-19  7:56     ` Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 12/14] objtool: Allow archs to rewrite retpolines Peter Zijlstra
2021-03-19  2:54   ` Josh Poimboeuf
2021-03-19 11:21     ` Peter Zijlstra
2021-03-19 13:28       ` Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 13/14] objtool: Skip magical retpoline .altinstr_replacement Peter Zijlstra
2021-03-18 17:11 ` [PATCH v2 14/14] objtool,x86: Rewrite retpoline thunk calls Peter Zijlstra
2021-03-19  3:29   ` Josh Poimboeuf
2021-03-19  8:06     ` Peter Zijlstra
2021-03-19 15:30       ` Josh Poimboeuf
2021-03-19 15:56         ` Peter Zijlstra [this message]
2021-03-19 22:52           ` Josh Poimboeuf

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