Date: Fri, 9 Aug 2019 10:01:31 -0600 From: Warner Losh <imp@bsdimp.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: 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: <CANCZdfodNPJqk5K5ckL4mWsYBwAC53J9afQFwNyhy59SNcULxg@mail.gmail.com> In-Reply-To: <20190809065733.GI2731@kib.kiev.ua> References: <201908081748.x78Hm79V085760@repo.freebsd.org> <20190808225947.GD1531@FreeBSD.org> <CANCZdfocZ6DVm7ASgMia0owvx9EPs-8NuH=bQzRZ=BXpLraQqw@mail.gmail.com> <20190809065733.GI2731@kib.kiev.ua>
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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. 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. 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)? Warnerhome | help
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