From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=90.155.92.199 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794472791; b=iPl37P97i2Kzb1bIB5BeZ1cbcWkm5ifBdRIMzMmZpaqjNVrjmvHGxyZxGcyvMElsb7o3 0CYGvyRaqTbvKXYMwvaoHMXBHmzsZ8gxIvzWpSvrPeJFUT/pcE3gEIaOHSIZDmR5B3eNP L3nWo4HZVZtIqZp2t0MYpbhDosspoG9Xn5GMawgTrdID08SG7krIsHzrGsY6BMtkA041O w1OjUtM7b4Gl+ol/y7cNJLzlPjrwEhwvmM5HUGGquFgPn7gs2TLMIsSrucxkElmsiKBj8 K7eulqRY3zmxG20l5aHpKVhNlqGN+/H6YeL++6Ii5gj3gv8Tj/w20W00bncgKQY/ong== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794472791; h=DMARC-Filter:DKIM-Signature:Received:Received:Date:From:To:Cc: Subject:Message-ID:References:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; bh=HoCxZnqDwVt70RG0ruGtLMnZF1f0PVlcRbSPjTQhqSY=; b=F6v78JlzFpMimaOokKRJ9zah3Tuak2G7vqK399Y1rfcAzXRoMZ03IiFnM09/o4412xbK Ud1rNECsLsnM64Cy3J+a+c0BUp5qeAl35Mbdd/RlUDiAZ1vyCAZJMheDRW/ZohRKrnNbr nf1uEYy4Y7rRRndmaD548z4MwjtRmpjWysKbjkFqxfbjE+PV+bEUZAF/hykc+zKyv+t1o usQlFw0kzvM2k6KvFf2+pHFyU4qxYSs8DmAWOTbmfvKqkYUB1AoSQgF07CX65L7iSIXxE +RYl/oTHhLr5xDqUfd+/cxCThTTAxvNBJFWh9ZPxzoTlkDNE2oQ66KOyT6kqHrcJqSQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=desiato.20200630 header.b=Mc1d85U7; arc=none smtp.remote-ip=90.155.92.199 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E1067606B385; Thu, 12 Nov 2026 08:39:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org E1067606B385 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=desiato.20200630 header.b=Mc1d85U7 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=HoCxZnqDwVt70RG0ruGtLMnZF1f0PVlcRbSPjTQhqSY=; b=Mc1d85U7R3WLHU95WhUzdkZxgV ozTHQCkjclHt9UTS4prS3VMsVNmWfjlvc7XhqH+HFB6+nasvs8/itX1bdWbFw2NpY6MUTl6+pkWMR hDAM6b19sQ5gp49s72iO5FSmiyPQCftKbLx6OhVskS8hYWRXhNEydcsHXuZi3A9mnYYvRIjpNfGS2 sTT3icVYicDyuc+q8SD1kIlYQyoZ9OV0ZuX5EE2SnaJ/UMgFKfNgoeY+mxAVZXCEXhKpsBV+eMNLr GvSrompn4wAl/mqMFdufyaPz0NqdPQuLd7FBGOLmKjraaBLFFDKKKP5zPSSrxu7qp12T8QIL4FssF 2vq4j43A==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.100.1 #2 (Red Hat Linux)) id 1xRQLS-0000000A4TG-2N2H; Thu, 12 Nov 2026 08:39:46 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 7506E30066A; Thu, 12 Nov 2026 09:39:45 +0100 (CET) Date: Thu, 12 Nov 2026 09:39:45 +0100 From: Peter Zijlstra To: Jiri Olsa Cc: Masami Hiramatsu , Naveen N Rao , "David S. Miller" , Josh Poimboeuf , Jason Baron , Alice Ryhl , Steven Rostedt , Ard Biesheuvel , Thomas Gleixner , Ingo Molnar , Alan Maguire , x86@kernel.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH 03/13] jump_label/x86: Avoid decoding instructions for jump entry size Message-ID: <20261112083945.GF2668804@noisy.programming.kicks-ass.net> References: <20261109194916.1089703-1-jolsa@kernel.org> <20261109194916.1089703-4-jolsa@kernel.org> X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261109194916.1089703-4-jolsa@kernel.org> On Mon, Nov 09, 2026 at 08:49:06PM +0100, Jiri Olsa wrote: > int arch_jump_entry_size(struct jump_entry *entry) > { > + const u8 *code = (void *)jump_entry_code(entry); > > + if (code[0] == JMP8_INSN_OPCODE || > + !memcmp(code, x86_nops[JMP8_INSN_SIZE], JMP8_INSN_SIZE)) > + return JMP8_INSN_SIZE; > > + if (code[0] == JMP32_INSN_OPCODE || > + !memcmp(code, x86_nops[JMP32_INSN_SIZE], JMP32_INSN_SIZE)) > + return JMP32_INSN_SIZE; > + > + BUG(); > } Does this actually generate sane code and checks code[0] first for both values before it goes and does memcmp() ? The naive translation would suggest it does not.