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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42b53e982d6sm28560143f8f.21.2025.11.17.14.09.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Nov 2025 14:09:55 -0800 (PST) Date: Mon, 17 Nov 2025 22:09:53 +0000 From: David Laight To: Alexandre Chartre Cc: Josh Poimboeuf , linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org Subject: Re: [PATCH v4 00/28] objtool: Function validation tracing Message-ID: <20251117220953.4f7bccc7@pumpkin> In-Reply-To: <3673c975-dc51-47ea-940b-8f09afa213a5@oracle.com> References: <20251113164917.2563486-1-alexandre.chartre@oracle.com> <3367da83-16b7-4c6a-bd08-d14ec4067025@oracle.com> <20251117094210.3c3e4f40@pumpkin> <81693206-9002-4669-ab74-fda3d31c25bb@oracle.com> <20251117123729.72ffa3e2@pumpkin> <3673c975-dc51-47ea-940b-8f09afa213a5@oracle.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 17 Nov 2025 14:11:55 +0100 Alexandre Chartre wrote: > On 11/17/25 13:37, David Laight wrote: > > On Mon, 17 Nov 2025 10:47:06 +0100 > > Alexandre Chartre wrote: > > > >> On 11/17/25 10:42, David Laight wrote: > > ... > >>> Although I think there ought to be some indication of the 31 NOP bytes > >>> at the end of the middle alternative. > >> > >> I am now compacting the code by removing all trailing NOPs. I should probably > >> improve that with printing the actual number of NOPs, for example NOP31 (or nop31) > > > > That is the sort of thing I was thinking of. > > Perhaps the actual opcodes on one line - eg: NOP5; NOP5; NOP5; NOP1 > > That might not always be very compact. For example __switch_to_asm() has 41 NOP1. > I will use NOP for now, and we can improve later. Could you use NOP1*41 (etc) so that NOP5*4 is different from NOP1*20? (I'm guessing you hand-decode the standard NOP sequences already?) Hmm... you don't want to execute that many 0x90 bytes. I think that case might have had a jump around them. Do I remember something about the trailing nop being merged? Perhaps that is the kernel patching code. Something made me think objtool might (also) be doing it. David