linux-kernel - Re: [PATCH v2 1/2] scripts: ftrace - move the sort-processing in ftrace

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Message-ID: <YZOstJy9mbZvHMUi@hirez.programming.kicks-ass.net>
Date:   Tue, 16 Nov 2021 14:05:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yinan Liu <yinan@...ux.alibaba.com>
Cc:     rostedt@...dmis.org, mark-pk.tsai@...iatek.com, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] scripts: ftrace - move the sort-processing in
 ftrace_init to compile time

On Tue, Nov 16, 2021 at 08:42:28PM +0800, Yinan Liu wrote:
> 
> 
> 在 2021/11/16 下午4:07, Peter Zijlstra 写道:
> 
> > /me hands a bucket of {} your way.
> 
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6406,8 +6406,10 @@ static int ftrace_process_locs(struct module *mod,
>         if (!count)
>                 return 0;
> 
> -       sort(start, count, sizeof(*start),
> -            ftrace_cmp_ips, NULL);
> +       if (mod) {
> +               sort(start, count, sizeof(*start),
> +                    ftrace_cmp_ips, NULL);
> +       }
> 
> hi，peter
> 
> you mean like this? I hope I'm not mistaken.

Exactly.

> 
> > Also, can't sorttable be ran on modules ?
> 
> The .ko file will be relocated after insmod or modprobe.
> And the mcount redirection in .ko is based on ".text",
> ".init.text", ".ref.text", ".sched.text", ".spinlock.text",
> ".irqentry .text", ".softirqentry.text", ".kprobes.text", ".cpuidle.text",
> ".text.unlikely". These sections‘ loading
> position are not in definite order.
> 
> So sorting this part at compile time doesn't make much sense.

Bah.. I thought the sections would retain relative position at least,
but alas. if that isn't done you're quite right that sorting seems
pointless.