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Message-ID: <20210519152205.GL10366@gate.crashing.org>
Date: Wed, 19 May 2021 10:22:05 -0500
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
Cc: "npiggin@...il.com" <npiggin@...il.com>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
"ldv@...linux.org" <ldv@...linux.org>,
"mpe@...erman.id.au" <mpe@...erman.id.au>,
"musl@...ts.openwall.com" <musl@...ts.openwall.com>,
"libc-dev@...ts.llvm.org" <libc-dev@...ts.llvm.org>,
"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: Linux powerpc new system call instruction and ABI
On Wed, May 19, 2021 at 03:06:49PM +0000, Joakim Tjernlund wrote:
> On Wed, 2021-05-19 at 09:38 -0500, Segher Boessenkool wrote:
> > On Wed, May 19, 2021 at 06:42:40PM +1000, Nicholas Piggin wrote:
> > > Excerpts from Joakim Tjernlund's message of May 19, 2021 6:08 pm:
> > > > I always figured the ppc way was superior. It begs the question if not the other archs should
> > > > change instead?
> > >
> > > It is superior in some ways, not enough to be worth being different.
> >
> > The PowerPC syscall ABI *requires* using cr0.3 for indicating errors,
> > you will have to do that whether you conflate the concepts of return
> > code and error indicator or not!
> >
> > > Other archs are unlikely to change because it would be painful for
> > > not much benefit.
> >
> > Other archs cannot easily change for much the same reason :-)
>
> Really? I figured you could just add extra error indication in kernel syscall I/F.
> Eventually user space could migrate to the new indication.
You seem to assume all user space uses glibc, or *any* libc even? This
is false. Some programs do system calls directly. Do not break the
kernel ABI :-)
Segher
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