linux-kernel - Re: [PATCH 5/7] powerpc/ftrace: Update ftrace

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Date:   Tue, 18 Jun 2019 11:45:09 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/7] powerpc/ftrace: Update ftrace_location() for
 powerpc -mprofile-kernel

On Tue, 18 Jun 2019 20:17:04 +0530
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:

> @@ -1551,7 +1551,7 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
>  	key.flags = end;	/* overload flags, as it is unsigned long */
>  
>  	for (pg = ftrace_pages_start; pg; pg = pg->next) {
> -		if (end < pg->records[0].ip ||
> +		if (end <= pg->records[0].ip ||

This breaks the algorithm. "end" is inclusive. That is, if you look for
a single byte, where "start" and "end" are the same, and it happens to
be the first ip on the pg page, it will be skipped, and not found.

-- Steve

>  		    start >= (pg->records[pg->index - 1].ip + MCOUNT_INSN_SIZE))
>  			continue;
>  		rec = bsearch(&key, pg->records, pg->index,