Messages in this thread | | | Date | Mon, 24 Aug 2009 20:34:32 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 05/12] update FTRACE_SYSCALL_MAX |
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* Paul Mundt <lethal@linux-sh.org> wrote:
> 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).
I agree with you - we should certainly add a clean and arch-generic way and drop the FTRACE_SYSCALL_MAX hack which really just tried to hide the arch differences for no strong reason.
At the same time the compat syscall space should be solved too, and a synonymous compat_NR_syscalls value introduced. (perhaps defined to 0 on non-compat kernels)
Ingo
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