Date: Fri, 9 Aug 2019 14:29:49 -0700 (PDT) From: "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Warner Losh <imp@bsdimp.com>, Gleb Smirnoff <glebius@freebsd.org>, Warner Losh <imp@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head <svn-src-head@freebsd.org> Subject: Re: svn commit: r350764 - head/sys/arm64/arm64 Message-ID: <201908092129.x79LTncP099313@gndrsh.dnsmgr.net> In-Reply-To: <20190809210505.GJ2731@kib.kiev.ua>
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> On Fri, Aug 09, 2019 at 10:01:31AM -0600, Warner Losh wrote: > > On Fri, Aug 9, 2019 at 12:57 AM Konstantin Belousov <kostikbel@gmail.com> > > wrote: > > > > > On Thu, Aug 08, 2019 at 07:38:28PM -0600, Warner Losh wrote: > > > > On Thu, Aug 8, 2019, 4:59 PM Gleb Smirnoff <glebius@freebsd.org> wrote: > > > > > > > > > Hi, > > > > > > > > > > why do we need COMPAT_43 for arm64 at all? I can't imagine an > > > > > application that would require this compatibility. > > > > > > > > > > A more general question is how far in the future are we going > > > > > to carry COMPAT_43 for i386/amd64? > > > > > > > > > > > > > COMPAT_43 is a weird option. It's a combo of both sys calls and kernel > > > > behavior modifications. Before we thinned the ABIs we supported, it was > > > > necessary for them as well. The biggest behavior change is around > > > signals. > > > > It is weird to sort out and nobody has done the deep analysis to see what > > > > is truly unused and what is there for compat with Linux and other SysV > > > > systems... > > > I am not aware of any changes that COMPAT_43 provides for the signal > > > handling semantic, except a minor adjustment for interpretation of > > > zero-sized stack for sigaltstack(2). > > > > > > > The onstack stuff was what I was thinking about, but we also have code in > > sys_getpid() that returns the ppid in the second retval register, and > > similar things for getuid and getgid, It also allows ioctl numbers that > > have IOC_IN set, but size == 0 (these would otherwise return ENOTTY). It > > also turns on the COMPAT_OLDSOCK code which generally only kicks in when > > compat bits are set, but in one place it allows a shorter unix domain > > socket path length to be compatible unconditionally. The compatibility TTY > > stuff, at least is under COMPAT_43TTY, but that's purely ioctl translation > > code. > I only reacted to the note about changing the signals syscalls behavior. > But the point is valid, we should not change the syscalls ABI for new > binaries when COMPAT_43 is enabled. I propose the following > https://reviews.freebsd.org/D21200 > > WRT ioctl code for no IOC_OUT and size == 0, I believe that this is in > fact cannot be changed. It is enabled also under COMPAT_FREEBSD4 and > 5, and we always enable these for GENERIC. So effectively this ioctl > permissive mode is always there. > > > > > The COMPAT_43 option indeed enables lcall 7,0 syscall entry emulation, > > > on both i386 and amd64. We are able to run FreeBSD 1.1.8 (i386) on amd64 > > > kernel in chroot this way. Since sometimes I get bug reports about this > > > stuff, there are some users of it. I believe it is important to be able > > > to run any FreeBSD binary for PR purposes, to wave the flag of excellent > > > binary compatibility we offer. > > > > > > COMPAT_43 is there to stay as far as there are people willing to maintain > > > it. There are more than one. > > > > > > > I think it's safe to retain on i386. amd64 is less clear to me, but I'd > > lean yes. > I believe amd64 is required since you have less and less chances to usefully > run i386 kernel on modern hardware. Would this also be required for running i386 binaries on amd64 using lib32 that expect the COMPAT_43 behavior? > > All the other platforms I'd agree with gleb: why do we need it in > > the kernels by default (and maybe why do we need to support it at all)? > > > > Warner -- Rod Grimes rgrimes@freebsd.org
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