linux-kernel - Re: [PATCH 5/5] x86/unwind/orc: delete dead write in __orc

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Date:   Fri, 11 Mar 2022 19:59:00 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] x86/unwind/orc: delete dead write in __orc_find()

On Fri, Mar 11, 2022 at 03:13:02PM +0000, David Laight wrote:
> From: Alexey Dobriyan
> > Sent: 11 March 2022 14:43
> > 
> > Also move "mid" variable to the innermost scope and delete useless
> > parenthesis while I'm at it.
> 
> Hiding the definition of 'mid' in the inner scope is pointless.

Not, it is not.

> I'm also not 100% sure that 'found' is always set.

"found" is left as-is by the patch.

> Consider the ip < orc_ip(first) case.

> > --- a/arch/x86/kernel/unwind_orc.c
> > +++ b/arch/x86/kernel/unwind_orc.c
> > @@ -35,7 +35,7 @@ static struct orc_entry *__orc_find(int *ip_table, struct orc_entry *u_table,
> >  {
> >  	int *first = ip_table;
> >  	int *last = ip_table + num_entries - 1;
> > -	int *mid = first, *found = first;
> > +	int *found = first;
> > 
> >  	if (!num_entries)
> >  		return NULL;
> > @@ -47,7 +47,7 @@ static struct orc_entry *__orc_find(int *ip_table, struct orc_entry *u_table,
> >  	 * ignored when they conflict with a real entry.
> >  	 */
> >  	while (first <= last) {
> > -		mid = first + ((last - first) / 2);
> > +		int *mid = first + (last - first) / 2;
> > 
> >  		if (orc_ip(mid) <= ip) {
> >  			found = mid;