From: Rich Felker <dalias@libc.org>
To: Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
Cc: "segher@kernel.crashing.org" <segher@kernel.crashing.org>,
"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>,
"npiggin@gmail.com" <npiggin@gmail.com>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
"libc-dev@lists.llvm.org" <libc-dev@lists.llvm.org>
Subject: Re: [musl] Re: Linux powerpc new system call instruction and ABI
Date: Wed, 19 May 2021 19:48:47 -0400 [thread overview]
Message-ID: <20210519234846.GS2546@brightrain.aerifal.cx> (raw)
In-Reply-To: <adec4377144a44b6f9ddd10c1b5256b80c9ceb50.camel@infinera.com>
On Wed, May 19, 2021 at 06:09:25PM +0000, Joakim Tjernlund wrote:
> On Wed, 2021-05-19 at 10:22 -0500, Segher Boessenkool wrote:
> > 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 :-)
>
> Adding an extra indicator does not break ABI, does it ?
It does, because the old ABI on most archs has no clobbers except the
return value register. Some archs though have additional
syscall-clobbered regs that could be repurposed as extra return
values, but you could only rely on them being meaningful after probing
for a kernel that speaks the new variant. This just makes things more
complicated, not more useful.
> W.r.t breaking ABI, isn't that what PowerPC is trying to do with the new syscall I/F?
No, it's a new independent interface.
Rich
next prev parent reply other threads:[~2021-05-19 23:49 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-11 8:12 [musl] " Nicholas Piggin
2020-06-11 8:12 ` [musl] [PATCH 1/2] powerpc/64s/exception: treat NIA below __end_interrupts as soft-masked Nicholas Piggin
2020-07-24 13:25 ` [musl] " Michael Ellerman
2020-06-11 8:12 ` [musl] [PATCH 2/2] powerpc/64s: system call support for scv/rfscv instructions Nicholas Piggin
2020-07-23 6:47 ` [musl] " Michael Ellerman
2020-07-23 16:48 ` Christophe Leroy
2020-07-24 10:45 ` Michael Ellerman
2020-06-11 21:02 ` [musl] Re: Linux powerpc new system call instruction and ABI Segher Boessenkool
2020-06-14 9:26 ` Nicholas Piggin
2021-05-18 23:13 ` Dmitry V. Levin
2021-05-19 2:50 ` Nicholas Piggin
2021-05-19 5:01 ` Nicholas Piggin
2021-05-21 19:40 ` Matheus Castanho
2021-05-21 19:52 ` Florian Weimer
2021-05-21 20:00 ` Matheus Castanho
2021-05-21 20:52 ` Dmitry V. Levin
2021-05-24 12:11 ` Matheus Castanho
2021-05-24 20:33 ` Matheus Castanho
2021-05-19 10:24 ` Dmitry V. Levin
2021-05-19 10:59 ` Nicholas Piggin
2021-05-19 12:39 ` Tulio Magno Quites Machado Filho
2021-05-19 13:26 ` Dmitry V. Levin
2021-05-19 22:51 ` Nicholas Piggin
2021-05-19 23:27 ` Dmitry V. Levin
2021-05-20 2:40 ` Nicholas Piggin
2021-05-20 3:06 ` Dmitry V. Levin
2021-05-20 5:12 ` Nicholas Piggin
2021-05-19 7:33 ` Joakim Tjernlund
2021-05-19 7:55 ` Nicholas Piggin
2021-05-19 8:08 ` Joakim Tjernlund
2021-05-19 8:42 ` Nicholas Piggin
2021-05-19 11:12 ` Nicholas Piggin
2021-05-19 14:38 ` Segher Boessenkool
2021-05-19 15:06 ` Joakim Tjernlund
2021-05-19 15:22 ` Segher Boessenkool
2021-05-19 15:36 ` Rich Felker
2021-05-19 18:09 ` Joakim Tjernlund
2021-05-19 23:48 ` Rich Felker [this message]
2021-05-20 1:06 ` Dmitry V. Levin
2021-05-20 2:45 ` Nicholas Piggin
2021-05-20 2:59 ` Dmitry V. Levin
2021-05-20 7:20 ` Nicholas Piggin
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