From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.esperi.org.uk (icebox.esperi.org.uk [81.187.191.129]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 82F434A35 for ; Tue, 28 Apr 2026 20:52:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=81.187.191.129 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777409531; cv=none; b=q16fGtYIaaqj06rwu7aK3y/44QzLXrS+7uOjxA527ntvzansBCvnvhQ36a5muad882fbnqzVORvnmjTRNRRRZrWPPQny7UaOMzcTii/ercjIRtOolCBMLOIHoclhj2Dkq4RXLdIjWer8xOpzQOFJnHLH+ru7YLLATZBtxMDApmY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777409531; c=relaxed/simple; bh=qouNh6UcUG4S/e0/ShThRuxY9m7r8+NyPiSnzhYERmI=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=c00geRBj9ymepxdc7BucZkUvRjhFal5dMCfFa8PbR1OLOXhGRFnbO5lVlSaTO/NnNh+hUYh90MvsBjbBaOfBKRKOAXaSZWb87YhcUDvE6gA7n0VswXQQ3T3n+gXpWRxaN3AyeKS2bHCY7yNmI2GUlNCDUqOU7QRzfKdfnp8qUN0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=esperi.org.uk; spf=pass smtp.mailfrom=esperi.org.uk; arc=none smtp.client-ip=81.187.191.129 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=esperi.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=esperi.org.uk Received: from loom (nix@sidle.srvr.nix [192.168.14.8]) by mail.esperi.org.uk (8.17.2/8.17.2) with ESMTPS id 63SKq4hx015856 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Tue, 28 Apr 2026 21:52:05 +0100 From: Nick Alcock To: Kris Van Hees Cc: dtrace@lists.linux.dev, dtrace-devel@oss.oracle.com Subject: Re: [PATCH 5/6] fbt: retrieve function return value using helper In-Reply-To: <3dc679a2ee099ae4e555e093422b17b6@oracle.com> (Kris Van Hees's message of "Tue, 28 Apr 2026 19:05:27 +0000") References: <3dc679a2ee099ae4e555e093422b17b6@oracle.com> Emacs: a learning curve that you can use as a plumb line. Date: Tue, 28 Apr 2026 21:52:04 +0100 Message-ID: <87jytqreob.fsf@esperi.org.uk> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: dtrace@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-DCC-wuwien-Metrics: loom 1290; Body=3 Fuz1=3 Fuz2=3 rep=17% On 28 Apr 2026, Kris Van Hees outgrape: > We were causing BPF verifier errors when trying to access the return value > of some functions due to incorrect calculation of the offset to read from. > Rather than implementing the more complex logic needed to calculate the > proper offset of the return value, we can just use the bpf_get_func_ret() > BPF helper. This does not impose a performance decrease because that > helper gets inlined by the BPF verifier. Presumably we are a suitable probe type? ... yes, we are. > Signed-off-by: Kris Van Hees Reviewed-by: Nick Alcock Looks much nicer. -- NULL && (void)