Date: Fri, 9 Aug 2019 09:57:33 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Warner Losh <imp@bsdimp.com> Cc: Gleb Smirnoff <glebius@freebsd.org>, Warner Losh <imp@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r350764 - head/sys/arm64/arm64 Message-ID: <20190809065733.GI2731@kib.kiev.ua> In-Reply-To: <CANCZdfocZ6DVm7ASgMia0owvx9EPs-8NuH=bQzRZ=BXpLraQqw@mail.gmail.com> References: <201908081748.x78Hm79V085760@repo.freebsd.org> <20190808225947.GD1531@FreeBSD.org> <CANCZdfocZ6DVm7ASgMia0owvx9EPs-8NuH=bQzRZ=BXpLraQqw@mail.gmail.com>
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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 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.
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