linux-kernel - Re: [PATCH 06/13] arc: define syscall_get

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Date:   Fri, 9 Nov 2018 16:11:21 +0000
From:   Alexey Brodkin <alexey.brodkin@...opsys.com>
To:     "luto@...capital.net" <luto@...capital.net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-audit@...hat.com" <linux-audit@...hat.com>,
        "vineet.gupta1@...opsys.com" <vineet.gupta1@...opsys.com>,
        "eparis@...hat.com" <eparis@...hat.com>,
        "ldv@...linux.org" <ldv@...linux.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "paul@...l-moore.com" <paul@...l-moore.com>,
        "lineprinter@...linux.org" <lineprinter@...linux.org>
Subject: Re: [PATCH 06/13] arc: define syscall_get_arch()

Hi Andy,

On Fri, 2018-11-09 at 07:56 -0800, Andy Lutomirski wrote:
> > On Nov 9, 2018, at 7:27 AM, Alexey Brodkin <alexey.brodkin@...opsys.com> wrote:
> > 
> > Hi Andy,
> > 
> > > On Fri, 2018-11-09 at 07:17 -0800, Andy Lutomirski wrote:
> > > On Fri, Nov 9, 2018 at 6:22 AM Alexey Brodkin
> > > <alexey.brodkin@...opsys.com> wrote:
> > > > Hi Dmitry,
> > > > 
> > > > > On Fri, 2018-11-09 at 06:16 +0300, Dmitry V. Levin wrote:
> > > > > syscall_get_arch() is required to be implemented on all architectures
> > > > > that use tracehook_report_syscall_entry() in order to extend
> > > > > the generic ptrace API with PTRACE_GET_SYSCALL_INFO request.
> > > > > 
> > > > > Signed-off-by: Dmitry V. Levin <ldv@...linux.org>
> > > > > ---
> > > > > arch/arc/include/asm/syscall.h | 6 ++++++
> > > > > include/uapi/linux/audit.h     | 1 +
> > > > > 2 files changed, 7 insertions(+)
> > > > 
> > > > [snip]
> > > > 
> > > > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > > > > index 818ae690ab79..a7149ceb5b98 100644
> > > > > --- a/include/uapi/linux/audit.h
> > > > > +++ b/include/uapi/linux/audit.h
> > > > > @@ -375,6 +375,7 @@ enum {
> > > > > 
> > > > > #define AUDIT_ARCH_AARCH64   (EM_AARCH64|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
> > > > > #define AUDIT_ARCH_ALPHA     (EM_ALPHA|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
> > > > > +#define AUDIT_ARCH_ARC               (EM_ARC)
> > > > 
> > > > Similarly here we need to have:
> > > > ---------------------------->8-----------------------------
> > > > +#define AUDIT_ARCH_ARC         (EM_ARC|EM_ARCV2)
> > > > ---------------------------->8-----------------------------
> > > > 
> > > 
> > > Huh?  How does the bitwise or of two ELF machine codes make any sense?
> > 
> > Oops... I didn't read examples of AUDIT_ARCH_ALPHA above :(
> > Indeed that was stupid.
> > 
> > But what would be a proper fix then?
> > 
> > Something like that?
> > ---------------------------->8-----------------------------
> > #define AUDIT_ARCH_ARC               (EM_ARC)
> > #define AUDIT_ARCH_ARCV2             (EM_ARCV2)
> > 
> > 
> > static inline int syscall_get_arch(void)
> > {
> > #ifdef __ARC700__
> >       return AUDIT_ARCH_ARC;
> > #else
> >       return AUDIT_ARCH_ARCV2;
> > #endif
> > }
> > ---------------------------->8-----------------------------
> > 
> 
> Maybe, but I know basically nothing about ARC.  Is the syscall numbering or calling convention different on ARC vs ARCv2?

Syscall numbering should be the same as we use UAPI for both ARCompact (AKA ARCv1)
and ARCv2. As for calling convention I think it indeed differs.

Note ARCompact and ARCv2 ISAs are binary incompatible!

Even though assembly look pretty much the same (sans instructions
available only for either ARCompact or ARCv2) encodings are different so
in that sense these are completely different architectures.

Also I'm wondering what could be other cases for use of syscall_get_arch().

So I'd say it's better to report different values for ARC ISAs.
And given we use the same values as in Binutils IMHO it would be good
to not mix IDs here.

-Alexey