Re: [PATCH 05/12] update FTRACE_SYSCALL_MAX

Paul Mundt
2009-08-24T14:15:41Z

On Mon, Aug 24, 2009 at 10:06:29AM -0400, Jason Baron wrote:
> On Mon, Aug 24, 2009 at 10:41:52PM +0900, Paul Mundt wrote:
> > 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.
>
NR_syscalls has always been the total number of system calls, not the
last one.

> > 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.
>

In today's -next:

#ifdef CONFIG_X86_64
# define FTRACE_SYSCALL_MAX 299
#else
# define FTRACE_SYSCALL_MAX 337
#endif

unistd_32.h:

#define __NR_reflinkat 337

unistd_64.h:

#define __NR_reflinkat 299

The first syscall starts at 0, but I don't see how this last syscall is
handled. If there were a __NR_syscalls 300 and 338 respectively, that
would seem to do the right thing. Or am I missing something?