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Date: Thu, 11 Jan 2018 16:02:57 +0800
From: Alan Kao <nonerkao@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Palmer Dabbelt <palmer@sifive.com>, Albert Ou <albert@sifive.com>,
        Ingo Molnar <mingo@redhat.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Kamil Rytarowski <n54@gmx.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        patches@groups.riscv.org, linux-kernel@vger.kernel.org,
        Alan Kao <alankao@andestech.com>,
        Greentime Hu <greentime@andestech.com>
Subject: Re: [PATCH 2/6] riscv/ftrace: Add dynamic function tracer support
Message-ID: <20180111080255.GA2848@93d8b218059b>
References: <20180110073814.32338-1-alankao@andestech.com>
 <20180110073814.32338-3-alankao@andestech.com>
 <20180110113643.7622a7d3@vmware.local.home>
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On Wed, Jan 10, 2018 at 11:36:43AM -0500, Steven Rostedt wrote:
> On Wed, 10 Jan 2018 15:38:10 +0800
> Alan Kao <nonerkao@gmail.com> wrote:
> 
> > +static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
> > +				bool enable)
> > +{
> > +	unsigned int offset = (unsigned int)(target - hook_pos);
> > +	unsigned int auipc_call = to_auipc_insn(offset);
> > +	unsigned int jalr_call = to_jalr_insn(offset);
> > +	unsigned int calls[2] = {auipc_call, jalr_call};
> > +	unsigned int nops[2] = {NOP4, NOP4};
> > +	int ret = 0;
> > +
> > +	/* when ftrace_make_nop is called */
> > +	if (!enable)
> > +		ret = ftrace_check_current_call(hook_pos, calls);
> > +
> > +	if (ret)
> > +		goto out;
> > +
> > +	/* replace the auipc-jalr pair at once */
> > +	ret = probe_kernel_write((void *)hook_pos, enable ? calls : nops,
> > +				 MCOUNT_INSN_SIZE);
> > +	if (ret)
> 
> You don't want to return the return of probe_kernel_write() here. For
> ftrace bug to work properly, if a fail to write occurs, you need to
> return -EPERM.
> 
> -- Steve
> 
Thanks for the correction and the style fix in the previous mail.
These problems will be fixed in the next version patch.

Alan