Date:   Tue, 17 May 2022 10:08:18 +0800
From:   Huacai Chen <chenhuacai@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     WANG Xuerui <kernel@...0n.name>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "<linux-arch@...r.kernel.org>" <linux-arch@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH V10 14/22] LoongArch: Add signal handling support

Hi, Eric,

On Mon, May 16, 2022 at 10:07 PM Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
> WANG Xuerui <kernel@...0n.name> writes:
>
> > Hi,
> >
> > On 5/15/22 21:48, Huacai Chen wrote:
> >> diff --git a/arch/loongarch/include/uapi/asm/sigcontext.h b/arch/loongarch/include/uapi/asm/sigcontext.h
> >> new file mode 100644
> >> index 000000000000..efeb8b3f8236
> >> --- /dev/null
> >> +++ b/arch/loongarch/include/uapi/asm/sigcontext.h
> >> @@ -0,0 +1,63 @@
> >> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> >> +/*
> >> + * Author: Hanlu Li <lihanlu@...ngson.cn>
> >> + *         Huacai Chen <chenhuacai@...ngson.cn>
> >> + *
> >> + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> >> + */
> >> +#ifndef _UAPI_ASM_SIGCONTEXT_H
> >> +#define _UAPI_ASM_SIGCONTEXT_H
> >> +
> >> +#include <linux/types.h>
> >> +#include <linux/posix_types.h>
> >> +
> >> +/* FP context was used */
> >> +#define USED_FP                      (1 << 0)
> >> +/* Load/Store access flags for address error */
> >> +#define ADRERR_RD            (1 << 30)
> >> +#define ADRERR_WR            (1 << 31)
> >>> I've searched GitHub globally, and my local glibc checkout, for usages
> >>> of these 3 constants, and there seems to be none; please consider
> >>> removing these if doable. We don't want cruft in uapi right from the
> >>> beginning.
> >> They will be used in our glibc, I promise.
> > Okay then. Seems simple enough, and from my quick grepping these appear to be
> > original creations -- not carried over from somewhere else, so it's already
> > highly likely that some of the userland tools need these anyway, just not
> > released yet.
>
> I can understand exporting these values but the names aren't very
> well namespaced at all.  Which means they could accidentially
> conflict with things.
>
> It would probably be better to do:
> SC_USED_FP
> SC_ADDRERR_RD
> SC_ADDRERR_WR
SC_ prefix is good, but ADRERR_RD/ADRERR_WR is used together with
SIGSEGV/SIGBUS, so I want to keep the same as BUS_ADRERR (a single D)
if possible.

>
> And with two D's please.  It breaks my fingers to have to
> make a typo like that on purpose.
>
> This is very much a bikeshed comment, but I think the
> bikeshed should be painted.
>
> >>>> +
> >>>> +struct sigcontext {
> >>>> +     __u64   sc_pc;
> >>>> +     __u64   sc_regs[32];
> >>>> +     __u32   sc_flags;
> >>>> +     __u64   sc_extcontext[0] __attribute__((__aligned__(16)));
> >>>> +};
> >>>> +
> >>>> +#define CONTEXT_INFO_ALIGN   16
> >>>> +struct _ctxinfo {
> >>>> +     __u32   magic;
> >>>> +     __u32   size;
> >>>> +     __u64   padding;        /* padding to 16 bytes */
> >>>> +};
> >>>> +
> >>>> +/* FPU context */
> >>>> +#define FPU_CTX_MAGIC                0x46505501
> >>>> +#define FPU_CTX_ALIGN                8
> >>>> +struct fpu_context {
> >>>> +     __u64   regs[32];
> >>>> +     __u64   fcc;
> >>>> +     __u32   fcsr;
> >>>> +};
> >>> The 3 structs above should already see usage downstream (glibc and other
> >>> low-level friends), so they probably shouldn't be touched by now. At
> >>> least I can't see problems.
> >>>> +
> >>>> +/* LSX context */
> >>>> +#define LSX_CTX_MAGIC                0x53580001
> >>>> +#define LSX_CTX_ALIGN                16
> >>>> +struct lsx_context {
> >>>> +     __u64   regs[2*32];
> >>>> +     __u64   fcc;
> >>>> +     __u32   fcsr;
> >>>> +     __u32   vcsr;
> >>>> +};
> >>>> +
> >>>> +/* LASX context */
> >>>> +#define LASX_CTX_MAGIC               0x41535801
> >>>> +#define LASX_CTX_ALIGN               32
> >>>> +struct lasx_context {
> >>>> +     __u64   regs[4*32];
> >>>> +     __u64   fcc;
> >>>> +     __u32   fcsr;
> >>>> +     __u32   vcsr;
> >>>> +};
> >>> Do we want to freeze the LSX/LASX layout this early, before any detail
> >>> of said extension are published? We'll need to update kernel later
> >>> anyway, so I'd recommend leaving them out for the initial bring-up.
> >> Yes, they are freezed.
> > Okay too, I remember these are the same values as in the old world, so it should
> > be easy to support both worlds at least in this regard.
>
> You know.  I really don't like this including code for hardware that may
> be frozen but is not publicly documented yet.  Especially when the plan
> is to publicly document the hardware.  It has the real problem that no
> one else can review the code.
>
> In ever design I have worked with there have been places where the
> people putting it together have had blind spots.  The only way I know to
> get past blind spots is to get as many people as possible looking,
> and to listen to the feedback.
>
> Given that neither lsx_context nor lasx_context are used in the kernel
> code yet I would very much prefer that their inclusion wait until there
> is actual code that needs them.
>
> If nothing else that will put the definitions in context so people can
> more easily see the big picture and understand how the pieces fit.
OK, I will remove lsx_context/lasx_context in the next version.

Huacai
>
> Eric

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