linux-kernel - Re: [PATCH v1 7/7] DCE/DSE: riscv: trim syscall tables

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Date:   Sat,  7 Oct 2023 21:35:44 +0800
From:   Zhangjin Wu <falcon@...ylab.org>
To:     arnd@...db.de
Cc:     falcon@...ylab.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
        tim.bird@...y.com, tanyuan@...ylab.org
Subject: Re: [PATCH v1 7/7] DCE/DSE: riscv: trim syscall tables

Hi, Arnd

> On Tue, Sep 26, 2023, at 00:43, Zhangjin Wu wrote:
> > When the maximum nr of the used syscalls is smaller than __NR_syscalls
> > (original syscalls total). It is able to update __NR_syscalls to
> > (maximum nr + 1) and further trim the '>= (maximum nr + 1)' part of the
> > syscall tables:
> >
> > For example:
> >
> >     sys_call_table [143] = {
> > 	[0 ... 143 - 1] = sys_ni_syscall,
> >         [64] = sys_write,
> >         [93] = sys_exit,
> >         [142] = sys_reboot,
> >     }
> >
> > The >= 143 part of the syscall tables can be trimmed.
> >
> > At the same time, the syscall >= 143 from user space must be ignored
> > from do_trap_ecall_u() of traps.c.
> >
> > Signed-off-by: Zhangjin Wu <falcon@...ylab.org>
> > ---
> >  arch/riscv/include/asm/unistd.h               |  2 ++
> >  arch/riscv/kernel/Makefile                    |  2 ++
> >  arch/riscv/kernel/syscalls/Makefile           | 22 +++++++++++++++++++
> >  .../kernel/syscalls/compat_syscall_table.c    |  4 ++--
> >  arch/riscv/kernel/syscalls/syscall_table.c    |  4 ++--
> >  5 files changed, 30 insertions(+), 4 deletions(-)
> 
> This bit feels like you are overoptimizing for a corner case:
> there is not much to be gained in terms of memory savings, but
> you add complexity in an area that I feel should be made common
> between architectures.
> 
> I hope to get back to working on consolidating both the
> syscall.tbl input files and the build infrastructure for them
> across architectures, and you make that harder here, so I'd
> prefer you to drop this part, at least until the code is
> shared across all architectures.
>

Agree, let's drop it.

Thanks,
Zhangjin

>     Arnd