linux-kernel - Re: [GIT PULL] ftrace: Changes for v6.17

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Message-ID: <20250731075318.45a2f84d@gandalf.local.home>
Date: Thu, 31 Jul 2025 07:53:18 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Mark Rutland <mark.rutland@....com>, Artem Sadovnikov
 <a.sadovnikov@...ras.ru>
Subject: Re: [GIT PULL] ftrace: Changes for v6.17

On Wed, 30 Jul 2025 16:15:21 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Tue, 29 Jul 2025 at 11:42, Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> >   In print_graph_proc() the pid_ptr string is of size 11, but the comment says
> >   /* sign + log10(MAX_INT) + '\0' */ which is actually 12.  
> 
> Lol. Quoting the ancient Greeks: "Math is hard, let's go shopping".
> 
> That said, the comment is garbage anyway.
> 
> Because "sign + log10(MAX_INT) + '\0'" really is just 11 - if you
> round or truncate.

I'm confused, sizeof("-2147483648") is equal to 12.

$ echo '
#include <stdio.h>
int main (int argc, char **argv)
{
        printf("%ld\n", sizeof("-2147483648"));
        return 0;
}' > maxchar.c

$ gcc -o maxchar maxchar.c
$ ./maxchar
12

> 
> So somebody may have actually done the math "correctly", but the math
> was just stated wrongly.
> 
> Much better to actually write things out properly instead of trying to be fancy.
> 
> Becasue might be more legible to actually write it out and let the
> compiler do things, ie just do
> 
>    // This includes the sign and the terminating '\0'
>    #define MAX_INT_CHARACTERS sizeof("-2147483648")
> 
> which doesn't require people to know - or think they know - logarithms.

Hmm, should we add that to a header file?

-- Steve