linux-kernel - Re: [RFC PATCH 4/5] csky: ftrace: Drop duplicate implementation of arch_check_ftrace

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Date:   Wed, 9 Jun 2021 23:47:30 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Punit Agrawal <punitagrawal@...il.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [RFC PATCH 4/5] csky: ftrace: Drop duplicate implementation of arch_check_ftrace_location()

On Wed, Jun 9, 2021 at 10:30 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> Hi Guo,
>
> On Wed, 9 Jun 2021 20:33:18 +0800
> Guo Ren <guoren@...nel.org> wrote:
>
> > csky using -mcount not -fpatchable-function-entry, so
> >                 /* Given address is not on the instruction boundary */
> >                 if ((unsigned long)p->addr != ftrace_addr)
> >                         return -EILSEQ;
> > all right?
>
> Even if -mcount is used, that check is still needed since the
> ftrace hooked address will be the ftrace_addr. If user tries to
> probe the second instruction in mcount code, kprobes needs to stop it.
Make sense. It guarantees p->addr is the first instruction of function
-mcount call site.

Thx

Acked-by: Guo Ren <guoren@...nel.org>

>
> Thank you,
>
> >
> > On Wed, Jun 9, 2021 at 6:51 PM Punit Agrawal <punitagrawal@...il.com> wrote:
> > >
> > > The csky specific arch_check_ftrace_location() shadows a weak
> > > implementation of the function in core code that offers the same
> > > functionality but with additional error checking.
> > >
> > > Drop the architecture specific function as a step towards further
> > > cleanup in core code.
> > >
> > > Signed-off-by: Punit Agrawal <punitagrawal@...il.com>
> > > Cc: Guo Ren <guoren@...ux.alibaba.com>
> > > ---
> > >  arch/csky/kernel/probes/ftrace.c | 7 -------
> > >  1 file changed, 7 deletions(-)
> > >
> > > diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c
> > > index ef2bb9bd9605..b388228abbf2 100644
> > > --- a/arch/csky/kernel/probes/ftrace.c
> > > +++ b/arch/csky/kernel/probes/ftrace.c
> > > @@ -2,13 +2,6 @@
> > >
> > >  #include <linux/kprobes.h>
> > >
> > > -int arch_check_ftrace_location(struct kprobe *p)
> > > -{
> > > -       if (ftrace_location((unsigned long)p->addr))
> > > -               p->flags |= KPROBE_FLAG_FTRACE;
> > > -       return 0;
> > > -}
> > > -
> > >  /* Ftrace callback handler for kprobes -- called under preepmt disabled */
> > >  void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
> > >                            struct ftrace_ops *ops, struct ftrace_regs *fregs)
> > > --
> > > 2.30.2
> > >
> >
> >
> > --
> > Best Regards
> >  Guo Ren
> >
> > ML: https://lore.kernel.org/linux-csky/
>
>
> --
> Masami Hiramatsu <mhiramat@...nel.org>



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/