linux-kernel - Re: [PATCH 05/12] update FTRACE_SYSCALL

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Date:	Mon, 24 Aug 2009 10:06:29 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Paul Mundt <lethal@...ux-sh.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	rostedt@...dmis.org, peterz@...radead.org,
	mathieu.desnoyers@...ymtl.ca, jiayingz@...gle.com,
	mbligh@...gle.com, lizf@...fujitsu.com
Subject: Re: [PATCH 05/12] update FTRACE_SYSCALL_MAX

On Mon, Aug 24, 2009 at 10:41:52PM +0900, Paul Mundt wrote:
> > On Mon, Aug 10, 2009 at 04:52:35PM -0400, Jason Baron wrote:
> > > update FTRACE_SYSCALL_MAX to the current number of syscalls
> > > 
> > > Signed-off-by: Jason Baron <jbaron@...hat.com>
> > > 
> > > ---
> > >  arch/x86/include/asm/ftrace.h |    4 ++--
> > >  1 files changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> > > index bd2c651..7113654 100644
> > > --- a/arch/x86/include/asm/ftrace.h
> > > +++ b/arch/x86/include/asm/ftrace.h
> > > @@ -30,9 +30,9 @@
> > >  
> > >  /* FIXME: I don't want to stay hardcoded */
> > >  #ifdef CONFIG_X86_64
> > > -# define FTRACE_SYSCALL_MAX     296
> > > +# define FTRACE_SYSCALL_MAX     299
> > >  #else
> > > -# define FTRACE_SYSCALL_MAX     333
> > > +# define FTRACE_SYSCALL_MAX     337
> > >  #endif
> > 
> > 
> > I don't remember why we had to use a hardcoded number.
> > Is there no way to keep being sync with the current number of
> > syscalls? We dwant to avoid patching the kernel each time we
> > have a new syscall :-)
> > 
> I hope you can clarify what the meaning of this is supposed to be
> exactly. Is this number supposed to be the last usable syscall, or is it
> supposed to be the equivalent of NR_syscalls?
> 

I am using as the equivalent of NR_syscalls.

> Presently on SH we have this as NR_syscalls - 1, while on s390 I see it
> is treated as NR_syscalls directly. s390 opencodes the NR_syscalls
> directly and so presently blows up in -next due to a missing
> FTRACE_SYSCALL_MAX definition:
> 
> 	http://kisskb.ellerman.id.au/kisskb/buildresult/1120523/
> 
> I was in the process of fixing that up when I noticed this difference.
> x86 seems to also treat this as NR_syscalls - 1, but that looks to me
> like there is an off-by-1 in arch_init_ftrace_syscalls() causing the last
> syscall to be skipped?

I don't see how its used as 'NR_syscalls - 1' on x86,
arch_init_ftrace_syscalls() does:

        for (i = 0; i < FTRACE_SYSCALL_MAX; i++) {
                meta = find_syscall_meta(psys_syscall_table[i]);
                syscalls_metadata[i] = meta;
        }

So the last syscall should not be skipped.

We should probably convert *all* the arches to be using NR_syscalls
directly.

thanks,

-Jason



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