From owner-freebsd-hackers@freebsd.org Tue Jun 12 18:13:27 2018 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 94164100F026 for ; Tue, 12 Jun 2018 18:13:27 +0000 (UTC) (envelope-from ben@bwidawsk.net) Received: from mail.bwidawsk.net (zangief.bwidawsk.net [107.170.211.233]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "bwidawsk.net", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 13B0D72CE6; Tue, 12 Jun 2018 18:13:27 +0000 (UTC) (envelope-from ben@bwidawsk.net) Received: by mail.bwidawsk.net (Postfix, from userid 5001) id 06947122809; Tue, 12 Jun 2018 11:13:19 -0700 (PDT) X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on zangief.bwidawsk.net X-Spam-Level: X-Spam-ASN: X-Spam-Status: No, score=-1.0 required=4.1 tests=ALL_TRUSTED=-1 shortcircuit=no autolearn=no autolearn_force=no version=3.4.1 Received: from mail.bwidawsk.net (unknown [134.134.139.93]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mail.bwidawsk.net (Postfix) with ESMTPSA id 18E2F122547; Tue, 12 Jun 2018 11:13:17 -0700 (PDT) Date: Tue, 12 Jun 2018 11:13:16 -0700 From: Ben Widawsky To: Brooks Davis Cc: Warner Losh , "freebsd-hackers@freebsd.org" , Mark Johnston Subject: Re: specifying alignment of loader files Message-ID: <20180612181316.e67bv44exkvhmtyv@mail.bwidawsk.net> References: <20180612170420.GD56138@raichu> <20180612171649.GE56138@raichu> <20180612175130.GF56138@raichu> <20180612181009.GA11238@spindle.one-eyed-alien.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180612181009.GA11238@spindle.one-eyed-alien.net> User-Agent: NeoMutt/20180323 X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 12 Jun 2018 18:13:27 -0000 On 18-06-12 18:10:09, Brooks Davis wrote: > On Tue, Jun 12, 2018 at 11:55:27AM -0600, Warner Losh wrote: > > On Tue, Jun 12, 2018 at 11:51 AM, Mark Johnston wrote: > > > > > On Tue, Jun 12, 2018 at 11:45:01AM -0600, Warner Losh wrote: > > > > On Tue, Jun 12, 2018 at 11:16 AM, Mark Johnston > > > wrote: > > > > > > > > > On Tue, Jun 12, 2018 at 11:11:25AM -0600, Warner Losh wrote: > > > > > > On Tue, Jun 12, 2018 at 11:04 AM, Mark Johnston > > > > > wrote: > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > I'm writing some code which processes a file loaded by the > > > loader. I > > > > > > > want the file's contents to be available at a certain alignment in > > > > > > > memory, and as far as I can see, the loader provides no alignment > > > > > > > guarantees today. The access will happen early enough during boot > > > that > > > > > > > making an aligned copy of the data will be awkward, so I'd like the > > > > > > > loader to provide the desired alignment. > > > > > > > > > > > > > > I'm considering adding a new "module_align" variable that would > > > specify > > > > > > > the alignment for a given file type, and plumb that through to > > > > > > > command_load(). Does anyone have an alternate suggestion, or an > > > > > > > objection to my proposal? > > > > > > > > > > > > > > > > > > > I thought the loader already did that for ELF sections... Why not > > > wrap > > > > > your > > > > > > file in such a segment? > > > > > > > > > > In this case it's a raw binary file (CPU microcode), and I want to be > > > > > able to load it without any modifications or wrappers. > > > > > > > > > > > > > How do you identify the type then? I'm ok in theory with this (though a > > > > variable is more flexible than needed), but that's my main concern. > > > What's > > > > the alignment required btw? > > > > > > It'd be a property of the type, e.g., > > > > > > cpu_ucode_name=/boot/firmware/... > > > cpu_ucode_align=16 > > > > > > I do feel like having a separate variable is overkill, but I can't see > > > a less invasive solution that isn't hacky. > > > > > > The required alignment for Intel is 16 bytes; I'm not yet sure whether > > > AMD has a required alignment. > > > > > > > OK. That seems sane. I was thinking it was more general than this, but I'm > > cool with what you've outlined. > > > > OTOH, wouldn't just loading all files on page boundaries suffice? > > Page boundaries might be too much on very small systems, but there's > a principled argument for 8-bytes just based on the aligment of > primative types so 16 (or even 64) isn't much of a stretch. 16-bytes > would future-proof for the CHERI variants that are likely to make > it to silicon. > > -- Brooks I think native cacheline size is a pretty safe yet more conservative than page size bet ie. me too for 64.