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    SubjectRe: [PATCH 05/12] update FTRACE_SYSCALL_MAX
    On Mon, Aug 24, 2009 at 10:42:28AM -0400, Jason Baron wrote:
    > On Mon, Aug 24, 2009 at 11:15:39PM +0900, Paul Mundt wrote:
    > > 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?
    >
    > No, you are right. When I changed the FTRACE_SYSCALL_MAX to 299, and
    > 337, there was no reflinkat syscall in the tree. So, it was equivalent
    > to NR_syscalls at that point in time. So that's where the confusion is.
    >
    > Clearly, all the more reason to drop FTRACE_SYSCALL_MAX and change to
    > NR_syscalls...
    >
    If FTRACE_SYSCALL_MAX is dropped then s390 will be fixed, and I'll take
    care of the sh update. If you want to hold off on adding NR_syscalls back
    to x86, then s390 will need a #define FTRACE_SYSCALL_MAX __NR_syscalls in
    arch/s390/include/asm/ftrace.h. Keeping FTRACE_SYSCALL_MAX around seems
    to be asking for trouble, though (although I don't know what the original
    rationale behind adding it was).


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