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Date:   Fri, 25 Feb 2022 00:55:20 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     x86@kernel.org, joao@overdrivepizza.com, hjl.tools@gmail.com,
        jpoimboe@redhat.com, andrew.cooper3@citrix.com,
        linux-kernel@vger.kernel.org, ndesaulniers@google.com,
        keescook@chromium.org, samitolvanen@google.com,
        mark.rutland@arm.com, alyssa.milburn@intel.com, mbenes@suse.cz,
        rostedt@goodmis.org, mhiramat@kernel.org,
        alexei.starovoitov@gmail.com
Subject: Re: [PATCH v2 12/39] x86/ibt,ftrace: Search for __fentry__ location
Message-Id: <20220225005520.c69be2fbdbd28028361792d9@kernel.org>
In-Reply-To: <20220224151322.714815604@infradead.org>
References: <20220224145138.952963315@infradead.org>
        <20220224151322.714815604@infradead.org>
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Hi Peter,

On Thu, 24 Feb 2022 15:51:50 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> Have ftrace_location() search the symbol for the __fentry__ location
> when it isn't at func+0 and use this for {,un}register_ftrace_direct().
> 
> This avoids a whole bunch of assumptions about __fentry__ being at
> func+0.
> 
> Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  kernel/trace/ftrace.c |   30 ++++++++++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
> 
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1578,7 +1578,24 @@ unsigned long ftrace_location_range(unsi
>   */
>  unsigned long ftrace_location(unsigned long ip)
>  {
> -	return ftrace_location_range(ip, ip);
> +	struct dyn_ftrace *rec;
> +	unsigned long offset;
> +	unsigned long size;
> +
> +	rec = lookup_rec(ip, ip);
> +	if (!rec) {
> +		if (!kallsyms_lookup_size_offset(ip, &size, &offset))
> +			goto out;
> +
> +		if (!offset)

Isn't this 'if (offset)' ?

> +			rec = lookup_rec(ip - offset, (ip - offset) + size);
> +	}
> +
> +	if (rec)
> +		return rec->ip;
> +
> +out:
> +	return 0;
>  }

Thank you,

>  
>  /**
> @@ -5110,11 +5127,16 @@ int register_ftrace_direct(unsigned long
>  	struct ftrace_func_entry *entry;
>  	struct ftrace_hash *free_hash = NULL;
>  	struct dyn_ftrace *rec;
> -	int ret = -EBUSY;
> +	int ret = -ENODEV;
>  
>  	mutex_lock(&direct_mutex);
>  
> +	ip = ftrace_location(ip);
> +	if (!ip)
> +		goto out_unlock;
> +
>  	/* See if there's a direct function at @ip already */
> +	ret = -EBUSY;
>  	if (ftrace_find_rec_direct(ip))
>  		goto out_unlock;
>  
> @@ -5222,6 +5244,10 @@ int unregister_ftrace_direct(unsigned lo
>  
>  	mutex_lock(&direct_mutex);
>  
> +	ip = ftrace_location(ip);
> +	if (!ip)
> +		goto out_unlock;
> +
>  	entry = find_direct_entry(&ip, NULL);
>  	if (!entry)
>  		goto out_unlock;
> 
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>