Re: Linux powerpc new system call instruction and ABI

From: Segher Boessenkool <segher@kernel.crashing.org>
To: Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
Cc: "npiggin@gmail.com" <npiggin@gmail.com>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"ldv@altlinux.org" <ldv@altlinux.org>,
	"mpe@ellerman.id.au" <mpe@ellerman.id.au>,
	"musl@lists.openwall.com" <musl@lists.openwall.com>,
	"libc-dev@lists.llvm.org" <libc-dev@lists.llvm.org>,
	"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>
Subject: Re: Linux powerpc new system call instruction and ABI
Date: Wed, 19 May 2021 10:22:05 -0500	[thread overview]
Message-ID: <20210519152205.GL10366@gate.crashing.org> (raw)
In-Reply-To: <11d62aa2488e51ec00fe77f24a1d7cdcc21af0b8.camel@infinera.com>

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