linux-kernel - Re: [PATCH v2 5/8] ftrace: Add swap_func to ftrace_process

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Message-ID: <Zs3zcwyygUk4_X8y@kernel.org>
Date: Tue, 27 Aug 2024 18:40:35 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Andreas Larsson <andreas@...sler.com>,
	Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>,
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	Dinh Nguyen <dinguyen@...nel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
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Subject: Re: [PATCH v2 5/8] ftrace: Add swap_func to ftrace_process_locs()

On Mon, Aug 26, 2024 at 01:29:09PM -0400, Steven Rostedt wrote:
> On Mon, 26 Aug 2024 09:55:29 +0300
> Mike Rapoport <rppt@...nel.org> wrote:
> 
> > From: Song Liu <song@...nel.org>
> > 
> > ftrace_process_locs sorts module mcount, which is inside RO memory. Add a
> > ftrace_swap_func so that archs can use RO-memory-poke function to do the
> > sorting.
> 
> Can you add the above as a comment above the ftrace_swap_func() function?

Sure.
 
> Thanks,
> 
> -- Steve
> 
> > 
> > Signed-off-by: Song Liu <song@...nel.org>
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> > ---
> >  include/linux/ftrace.h |  2 ++
> >  kernel/trace/ftrace.c  | 13 ++++++++++++-
> >  2 files changed, 14 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> > index fd5e84d0ec47..b794dcb7cae8 100644
> > --- a/include/linux/ftrace.h
> > +++ b/include/linux/ftrace.h
> > @@ -1188,4 +1188,6 @@ unsigned long arch_syscall_addr(int nr);
> >  
> >  #endif /* CONFIG_FTRACE_SYSCALLS */
> >  
> > +void ftrace_swap_func(void *a, void *b, int n);
> > +
> >  #endif /* _LINUX_FTRACE_H */
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 4c28dd177ca6..9829979f3a46 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -6989,6 +6989,17 @@ static void test_is_sorted(unsigned long *start,
> > unsigned long count) }
> >  #endif
> >  
> > +void __weak ftrace_swap_func(void *a, void *b, int n)
> > +{
> > +	unsigned long t;
> > +
> > +	WARN_ON_ONCE(n != sizeof(t));
> > +
> > +	t = *((unsigned long *)a);
> > +	*(unsigned long *)a = *(unsigned long *)b;
> > +	*(unsigned long *)b = t;
> > +}
> > +
> >  static int ftrace_process_locs(struct module *mod,
> >  			       unsigned long *start,
> >  			       unsigned long *end)
> > @@ -7016,7 +7027,7 @@ static int ftrace_process_locs(struct module *mod,
> >  	 */
> >  	if (!IS_ENABLED(CONFIG_BUILDTIME_MCOUNT_SORT) || mod) {
> >  		sort(start, count, sizeof(*start),
> > -		     ftrace_cmp_ips, NULL);
> > +		     ftrace_cmp_ips, ftrace_swap_func);
> >  	} else {
> >  		test_is_sorted(start, count);
> >  	}
> 

-- 
Sincerely yours,
Mike.