Re: [PATCH 1/2] mips: convert syscall to generic entry

[Thomas Bogendoerfer <tsbogend@alpha.franken.de>]

On Wed, Sep 08, 2021 at 10:08:47AM +0800, 陈飞扬 wrote:
> On Tue, 7 Sept 2021 at 21:49, Jiaxun Yang <jiaxun.yang@flygoat.com> wrote:
> >
> >
> > 在 2021/9/7 14:16, FreeFlyingSheep 写道:
> > > From: Feiyang Chen <chenfeiyang@loongson.cn>
> > >
> > > Convert mips syscall to use the generic entry infrastructure from
> > > kernel/entry/*.
> > >
> > > There are a few special things on mips:
> > >
> > > - There is one type of syscall on mips32 (scall32-o32) and three types
> > > of syscalls on mips64 (scall64-o32, scall64-n32 and scall64-n64). Now
> > > convert to C code to handle different types of syscalls.
> > >
> > > - For some special syscalls (e.g. fork, clone, clone3 and sysmips),
> > > save_static_function() wrapper is used to save static registers. Now
> > > SAVE_STATIC is used in handle_sys before calling do_syscall(), so the
> > > save_static_function() wrapper can be removed.
> > >
> > > - For sigreturn/rt_sigreturn and sysmips, inline assembly is used to
> > > jump to syscall_exit directly for skipping setting the error flag and
> > > restoring all registers. Now use regs->regs[27] to mark whether to
> > > handle the error flag and always restore all registers in handle_sys,
> > > so these functions can return normally as other architecture.
> >
> > Hmm, that would give us overhead of register context on these syscalls.
> >
> > I guess it's worthy?
> >
> 
> Hi, Jiaxun,
> 
> Saving and restoring registers against different system calls can be
> difficult due to the use of generic entry.
> To avoid a lot of duplicate code, I think the overhead is worth it.

could you please provide numbers for that ? This code still runs
on low end MIPS CPUs for which overhead might mean a different
ballpark than some highend Loongson CPUs.

Thomas.

-- 
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