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[81.157.241.155]) by smtp.gmail.com with ESMTPSA id f197sm1373147wme.22.2019.08.22.13.45.01 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 22 Aug 2019 13:45:02 -0700 (PDT) Subject: Re: [RFC v4 07/18] objtool: Introduce INSN_UNKNOWN type To: Josh Poimboeuf , Raphael Gault Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, peterz@infradead.org, catalin.marinas@arm.com, will.deacon@arm.com, raph.gault+kdev@gmail.com References: <20190816122403.14994-1-raphael.gault@arm.com> <20190816122403.14994-8-raphael.gault@arm.com> <20190822200406.jc3yf77pomxxwep6@treble> From: Julien Message-ID: <3c4e3227-eeb3-371a-d015-a0e0e60e5332@gmail.com> Date: Thu, 22 Aug 2019 21:45:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <20190822200406.jc3yf77pomxxwep6@treble> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Josh, On 22/08/19 21:04, Josh Poimboeuf wrote: > On Fri, Aug 16, 2019 at 01:23:52PM +0100, Raphael Gault wrote: >> On arm64 some object files contain data stored in the .text section. >> This data is interpreted by objtool as instruction but can't be >> identified as a valid one. In order to keep analysing those files we >> introduce INSN_UNKNOWN type. The "unknown instruction" warning will thus >> only be raised if such instructions are uncountered while validating an >> execution branch. >> >> This change doesn't impact the x86 decoding logic since 0 is still used >> as a way to specify an unknown type, raising the "unknown instruction" >> warning during the decoding phase still. >> >> Signed-off-by: Raphael Gault > > Is there a reason such data can't be moved to .rodata? That would seem > like the proper fix. > Raphaël can confirm, if I remember correctly, that issue was encountered on assembly files implementing crypto algorithms were some words/double-words of data were in the middle of the .text. I think it is done this way to make sure the data can be loaded in a single instruction. So moving it to another section could impact the crypto performance depending on the relocations. That was my understanding at least. Cheers, -- Julien Thierry