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Date:   Mon, 12 Oct 2020 09:12:36 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Josh Poimboeuf <jpoimboe@redhat.com>
Cc:     Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Masami Hiramatsu <mhiramat@kernel.org>, x86 <x86@kernel.org>
Subject: Re: [tip: objtool/core] x86/insn: Support big endian cross-compiles
Message-Id: <20201012091236.0f9a64bfedb8825732b65ea5@kernel.org>
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        <20201009203822.GA2974@worktop.programming.kicks-ass.net>
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        <20201010174415.zwopoy6vpficoqlr@treble>
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On Sat, 10 Oct 2020 12:44:15 -0500
Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> On Fri, Oct 09, 2020 at 10:49:21PM +0200, Borislav Petkov wrote:
> > On Fri, Oct 09, 2020 at 10:38:22PM +0200, Peter Zijlstra wrote:
> > > On Wed, Oct 07, 2020 at 04:20:19PM -0000, tip-bot2 for Martin Schwidefsky wrote:
> > > > The following commit has been merged into the objtool/core branch of tip:
> > > > 
> > > > Commit-ID:     2a522b53c47051d3bf98748418f4f8e5f20d2c04
> > > > Gitweb:        https://git.kernel.org/tip/2a522b53c47051d3bf98748418f4f8e5f20d2c04
> > > > Author:        Martin Schwidefsky <schwidefsky@de.ibm.com>
> > > > AuthorDate:    Mon, 05 Oct 2020 17:50:31 +02:00
> > > > Committer:     Josh Poimboeuf <jpoimboe@redhat.com>
> > > > CommitterDate: Tue, 06 Oct 2020 09:32:29 -05:00
> > > > 
> > > > x86/insn: Support big endian cross-compiles
> > > > 
> > > > x86 instruction decoder code is shared across the kernel source and the
> > > > tools. Currently objtool seems to be the only tool from build tools needed
> > > > which breaks x86 cross compilation on big endian systems. Make the x86
> > > > instruction decoder build host endianness agnostic to support x86 cross
> > > > compilation and enable objtool to implement endianness awareness for
> > > > big endian architectures support.
> > > > 
> > > > Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
> > > > Co-developed-by: Vasily Gorbik <gor@linux.ibm.com>
> > > > Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
> > > > Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
> > > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > > 
> > > This commit breaks the x86 build with CONFIG_X86_DECODER_SELFTEST=y.
> > > 
> > > I've asked Boris to truncate tip/objtool/core.
> > 
> > Yeah, top 4 are gone until this is resolved.
> 
> Masami, I wonder if we even need these selftests anymore?  Objtool
> already decodes the entire kernel.

No, they have different roles. The selftest checks if the decoder
works correctly by comparing with the output of objdump.

As far as I can see, the objtool relies on the sanity of the decoder
(it trusts the output of the decoder).

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>