linux-kernel - Re: [PATCH 2/7] tracing: Change strlen to sizeof for hist trigger static strings

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Message-ID: <0c78a59b1dcb05237f35bb9c9714debfa96680c7.camel@perches.com>
Date:   Wed, 19 Dec 2018 13:08:20 -0800
From:   Joe Perches <joe@...ches.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Tom Zanussi <zanussi@...nel.org>
Cc:     tglx@...utronix.de, mhiramat@...nel.org, namhyung@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel@...lfernandes.org, mathieu.desnoyers@...icios.com,
        julia@...com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH 2/7] tracing: Change strlen to sizeof for hist trigger
 static strings

On Wed, 2018-12-19 at 16:01 -0500, Steven Rostedt wrote:
> On Wed, 19 Dec 2018 14:38:39 -0600
> Tom Zanussi <zanussi@...nel.org> wrote:
> 
> > On Wed, 2018-12-19 at 15:30 -0500, Steven Rostedt wrote:
> > > On Wed, 19 Dec 2018 12:20:19 -0800
> > > Joe Perches <joe@...ches.com> wrote:
> > >   
> > > > > Yeah, I had considered it but wasn't sure it was worth it.  Since
> > > > > you're suggesting it is, I can send another patch on top of
> > > > > these, or
> > > > > feel free if you want to too.  ;-)    
> > > > 
> > > > I believe the 'strlen("foo") -> sizeof("foo") - 1'
> > > > conversions do not change objects at all.
> > > > 
> > > > strlen("constant") is already optimized by gcc to a
> > > > constant value when fed a constant string.  
> > > 
> > > If that's the case (and it probably is), then yeah, strlen is
> > > probably
> > > better. As it can handle the "not a constant" that you stated in
> > > another email.
> > >   
> > 
> > OK, so I guess that means we should just drop this patch ('[PATCH 2/7]
> > tracing: Change strlen to sizeof for hist trigger static strings').
> > 
> 
> No, that patch is fine, the macro was not. I've already applied your
> patch set. Just need to run it through my tests.

The patch included:

-	start += strlen("char[");
+	start += sizeof("char[") - 1;

So, that 2/7 patch is unnecessary as there is no object code
change and using 'sizeof("const") - 1' is less intelligible
than strlen("const")

If you convert the strncmp(ptr, "const", strlen("const"))
uses to strncmp_prefix(ptr, "const") eventually, the patch
just makes more variations to change.