linux-kernel - Re: [PATCH v2] x86/insn, tools/x86: Fix some potential undefined behavior.

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Message-ID: <20201016093724.GH2611@hirez.programming.kicks-ass.net>
Date:   Fri, 16 Oct 2020 11:37:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     hpa@...or.com
Cc:     Ian Rogers <irogers@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org,
        Adrian Hunter <adrian.hunter@...el.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Numfor Mbiziwo-Tiapo <nums@...gle.com>
Subject: Re: [PATCH v2] x86/insn, tools/x86: Fix some potential undefined
 behavior.

On Thu, Oct 15, 2020 at 02:34:57PM -0700, hpa@...or.com wrote:
> Wait, what?
> 
> You are taking about x86-specific code, and on x86 unaligned memory
> accesses are supported, well-defined, and ubiquitous. 

Objtool uses this x86 instruction decoder, people are cross-buildling
objtool to cross-build x86 kernels.

So it's entirely possible to run the x86 insn decode on BE RISC, which
very much doesn't like unaligned loads.