Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 15 Sep 2022 10:47:01 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Chen Zhongjin <chenzhongjin@huawei.com>
Cc:     Michael Matz <matz@suse.de>, Borislav Petkov <bp@alien8.de>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        linux-toolchains@vger.kernel.org,
        Indu Bhagat <indu.bhagat@oracle.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-kernel@vger.kernel.org, "Jose E. Marchesi" <jemarch@gnu.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Mark Rutland <mark.rutland@arm.com>,
        Will Deacon <will@kernel.org>, x86@kernel.org,
        linux-arm-kernel@lists.infradead.org,
        live-patching@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Ard Biesheuvel <ardb@kernel.org>,
        Sathvika Vasireddy <sv@linux.ibm.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Mark Brown <broonie@kernel.org>
Subject: Re: [RFC] Objtool toolchain proposal:
 -fannotate-{jump-table,noreturn}
Message-ID: <YyLmhUxTUaNzaieC@hirez.programming.kicks-ass.net>
References: <20220909180704.jwwed4zhwvin7uyi@treble>
 <Yx8PcldkdOLN8eaw@nazgul.tnic>
 <alpine.LSU.2.20.2209121200120.8265@wotan.suse.de>
 <6a61aa57-141f-039c-5a2d-b2d79fecb8c2@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <6a61aa57-141f-039c-5a2d-b2d79fecb8c2@huawei.com>
Precedence: bulk

On Thu, Sep 15, 2022 at 10:56:58AM +0800, Chen Zhongjin wrote:

> We have found some anonymous information on x86 in .rodata.

Well yes, but that's still a bunch of heuristics on our side.

> I'm not sure if those are *all* of Josh wanted on x86, however for arm64 we
> did not found that in the same section so it is a problem on arm64 now.

Nick found Bolt managed the ARM64 jumptables:

  https://github.com/llvm/llvm-project/blob/main/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp#L484

But that does look like a less than ideal solution too.

> Does the compiler will emit these for all arches? At lease I tried and
> didn't find anything meaningful (maybe I omitted it).

That's the question; can we get the compiler to help us here in a well
defined manner.