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 23:29:59 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Guo Ren <guoren@...nel.org>
Cc:     Punit Agrawal <punitagrawal@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "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()

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.

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>