linux-kernel - Re: [PATCH v3 16/16] objtool,x86: Rewrite retpoline thunk calls

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Message-ID: <YL+0MO/1Ra1tnzhT@hirez.programming.kicks-ass.net>
Date:   Tue, 8 Jun 2021 20:17:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Fāng-ruì Sòng <maskray@...gle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>, lma@...ihalf.com,
        Guenter Roeck <groeck@...gle.com>,
        Juergen Gross <jgross@...e.com>, lb@...ihalf.com,
        LKML <linux-kernel@...r.kernel.org>, mbenes@...e.com,
        Radosław Biernacki <rad@...ihalf.com>,
        upstream@...ihalf.com,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH v3 16/16] objtool,x86: Rewrite retpoline thunk calls

On Tue, Jun 08, 2021 at 10:29:56AM -0700, Nathan Chancellor wrote:
> On 6/8/2021 10:22 AM, Peter Zijlstra wrote:

> > Since it's a VM, can you use the gdb-stub to ask it where it's stuck?
> > 
> 
> Unfortunately, this is the VM provided by the Windows Subsystem for Linux so
> examining it is nigh-impossible :/ I am considering bisecting the transforms
> that objtool does to try and figure out the one that causes the machine to
> fail to boot or try to reproduce in a different hypervisor, unless you have
> any other ideas.

Does breaking Windows earn points similar to breaking the binary
drivers? :-) :-)

The below should kill this latest transform and would quickly confirm if
the that is causing your problem. If that's not it, what was your last
known working version?


diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e5947fbb9e7a..d0f231b9c5a1 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1857,10 +1857,10 @@ static int decode_sections(struct objtool_file *file)
 	 * Must be after add_special_section_alts(), since this will emit
 	 * alternatives. Must be after add_{jump,call}_destination(), since
 	 * those create the call insn lists.
-	 */
 	ret = arch_rewrite_retpolines(file);
 	if (ret)
 		return ret;
+	 */
 
 	return 0;
 }