From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/14927 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH 0/6] updates for linux v5.3 Date: Tue, 12 Nov 2019 12:16:06 +0100 Message-ID: <20191112111606.GE25646@port70.net> References: <20191110010802.GC25646@port70.net> <20191110061409.GM16318@brightrain.aerifal.cx> <20191110120253.GD25646@port70.net> <20191112030150.GQ16318@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="154909"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Mutt/1.10.1 (2018-07-13) To: musl@lists.openwall.com Original-X-From: musl-return-14943-gllmg-musl=m.gmane.org@lists.openwall.com Tue Nov 12 12:16:21 2019 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.89) (envelope-from ) id 1iUU9l-000eAb-BT for gllmg-musl@m.gmane.org; Tue, 12 Nov 2019 12:16:21 +0100 Original-Received: (qmail 16114 invoked by uid 550); 12 Nov 2019 11:16:18 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 16096 invoked from network); 12 Nov 2019 11:16:18 -0000 Mail-Followup-To: musl@lists.openwall.com Content-Disposition: inline In-Reply-To: <20191112030150.GQ16318@brightrain.aerifal.cx> Xref: news.gmane.org gmane.linux.lib.musl.general:14927 Archived-At: * Rich Felker [2019-11-11 22:01:50 -0500]: > On Sun, Nov 10, 2019 at 01:02:53PM +0100, Szabolcs Nagy wrote: > > * Rich Felker [2019-11-10 01:14:09 -0500]: > > > On Sun, Nov 10, 2019 at 02:08:02AM +0100, Szabolcs Nagy wrote: > > > > >From 560fd1ebe616fd59c0abcaf86bec6109bfcd2141 Mon Sep 17 00:00:00 2001 > > > > From: Szabolcs Nagy > > > > Date: Sun, 3 Nov 2019 22:45:05 +0000 > > > > Subject: [PATCH 4/6] sys/ptrace.h: add PTRACE_GET_SYSCALL_INFO from linux v5.3 > > > > > > > > ptrace API to get details of the syscall the tracee is blocked in, see > > > > > > > > linux commit 201766a20e30f982ccfe36bebfad9602c3ff574a > > > > ptrace: add PTRACE_GET_SYSCALL_INFO request > > > > > > > > the align attribute was used to keep the layout the same across targets > > > > e.g. on m68k uint32_t is 2 byte aligned, this helps with compat ptrace. > > > > > > Can you explain the motivation for this? At first I thought it was for > > > overall alignment of the structure, but there are also 64-bit members > > > that aren't aligned, so presumably this is only to get padding after > > > the initial uint8_t? If so, just add 3 explicit padding members: > > > > the original linux struct had padding but during > > review they changed it to aligned because some > > linux devs thought that made the intent clearer > > or more future proof (e.g. what if uint64_t is > > also 2byte aligned, but on the 64bit version of > > the same architecture it's 8byte aligned, then > > compat ptrace would not work because one abi > > would have padding and the other wouldnt). > > I don't follow that line of reasoning; the alignment would potentially > differ, but the layout wouldn't, and that's why I initially suspected > they were doing this for alignment. In any case, the only arch without > at least 4-byte alignment is m68k, and it's not going to have a 64-bit > version. why would the layout be the same? uint8_t x; uint64_t y; // aligned to 2 bytes and uint8_t x; uint64_t y; // aligned to 4 bytes should have different layout (1 vs 3 bytes padding). > > > i guess for musl either works, but the current > > struct is how it is defined in glibc. > > Generally in musl we prefer not using extensions in public headers > except where the effect can be achieved in no other way. Only m68k is > affected by using the forced alignment here, but I don't think there's > any strong reason to prefer one way or the other. I think I'd want to > include the padding even if we do also include > _Alignas/alignas/__attribute__((__aligned__)) (dependent on language > version macros) so that in the fallback case the layout is still > correct even if the alignment isn't (on m68k only). ok with me.