2 * linux/arch/cris/entry.S
4 * Copyright (C) 2000, 2001, 2002 Axis Communications AB
6 * Authors: Bjorn Wesen (bjornw@axis.com)
10 * entry.S contains the system-call and fault low-level handling routines.
12 * NOTE: This code handles signal-recognition, which happens every time
13 * after a timer-interrupt and after each system call.
15 * Stack layout in 'ret_from_system_call':
16 * ptrace needs to have all regs on the stack.
17 * if the order here is changed, it needs to be
18 * updated in fork.c:copy_process, signal.c:do_signal,
19 * ptrace.c and ptrace.h
23 #include <linux/linkage.h>
24 #include <linux/sys.h>
25 #include <asm/unistd.h>
26 #include <asm/arch/sv_addr_ag.h>
27 #include <asm/errno.h>
28 #include <asm/thread_info.h>
29 #include <asm/asm-offsets.h>
31 #include <asm/pgtable.h>
33 ;; functions exported from this file
39 .globl multiple_interrupt
42 .globl spurious_interrupt
46 .globl gdb_handle_breakpoint
49 ;; below are various parts of system_call which are not in the fast-path
52 ; Check if preemptive kernel scheduling should be done
55 ; Load current task struct
56 movs.w -8192, $r0 ; THREAD_SIZE = 8192
58 move.d [$r0+TI_preempt_count], $r10 ; Preemption disabled?
62 move.d [$r0+TI_flags], $r10
63 btstq TIF_NEED_RESCHED, $r10 ; Check if need_resched is set
66 ; Ok, lets's do some preemptive kernel scheduling
67 jsr preempt_schedule_irq
68 ; Load new task struct
69 movs.w -8192, $r0 ; THREAD_SIZE = 8192
71 ; One more time (with new task)
75 #define _resume_kernel _Rexit
78 ; Called at exit from fork. schedule_tail must be called to drop
79 ; spinlock if CONFIG_PREEMPT
86 ;; check for resched if preemptive kernel or if we're going back to user-mode
87 ;; this test matches the user_regs(regs) macro
88 ;; we cannot simply test $dccr, because that does not necessarily
89 ;; reflect what mode we'll return into.
91 move.d [$sp + PT_dccr], $r0; regs->dccr
94 ; Note that di below is in delay slot
97 di ; so need_resched and sigpending don't change
99 movs.w -8192, $r0 ; THREAD_SIZE == 8192
102 move.d [$r0+TI_flags], $r10 ; current->work
103 and.d _TIF_WORK_MASK, $r10 ; is there any work to be done on return
109 ;; The system_call is called by a BREAK instruction, which works like
110 ;; an interrupt call but it stores the return PC in BRP instead of IRP.
111 ;; Since we dont really want to have two epilogues (one for system calls
112 ;; and one for interrupts) we push the contents of BRP instead of IRP in the
113 ;; system call prologue, to make it look like an ordinary interrupt on the
116 ;; Since we can't have system calls inside interrupts, it should not matter
117 ;; that we don't stack IRP.
119 ;; In r9 we have the wanted syscall number. Arguments come in r10,r11,r12,r13,mof,srp
121 ;; This function looks on the _surface_ like spaghetti programming, but it's
122 ;; really designed so that the fast-path does not force cache-loading of non-used
123 ;; instructions. Only the non-common cases cause the outlined code to run..
126 ;; stack-frame similar to the irq heads, which is reversed in ret_from_sys_call
127 move $brp,[$sp=$sp-16]; instruction pointer and room for a fake SBFS frame
131 subq 14*4, $sp ; make room for r0-r13
132 movem $r13, [$sp] ; push r0-r13
133 push $r10 ; push orig_r10
134 clear.d [$sp=$sp-4] ; frametype == 0, normal stackframe
137 move.d $r0, [$sp+PT_r10] ; put the default return value in r10 in the frame
139 ;; check if this process is syscall-traced
141 movs.w -8192, $r0 ; THREAD_SIZE == 8192
144 move.d [$r0+TI_flags], $r0
145 btstq TIF_SYSCALL_TRACE, $r0
146 bmi _syscall_trace_entry
151 ;; check for sanity in the requested syscall number
153 cmpu.w NR_syscalls, $r9
154 bcc ret_from_sys_call
155 lslq 2, $r9 ; multiply by 4, in the delay slot
157 ;; as a bonus 7th parameter, we give the location on the stack
158 ;; of the register structure itself. some syscalls need this.
162 ;; the parameter carrying registers r10, r11, r12 and 13 are intact.
163 ;; the fifth and sixth parameters (if any) was in mof and srp
164 ;; respectively, and we need to put them on the stack.
169 jsr [$r9+sys_call_table] ; actually do the system call
170 addq 3*4, $sp ; pop the mof, srp and regs parameters
171 move.d $r10, [$sp+PT_r10] ; save the return value
173 moveq 1, $r9 ; "parameter" to ret_from_sys_call to show it was a sys call
175 ;; fall through into ret_from_sys_call to return
178 ;; r9 is a parameter - if >=1 we came from a syscall, if 0, from an irq
180 ;; get the current task-struct pointer (see top for defs)
182 movs.w -8192, $r0 ; THREAD_SIZE == 8192
185 di ; make sure need_resched and sigpending don't change
186 move.d [$r0+TI_flags],$r1
187 and.d _TIF_ALLWORK_MASK, $r1
188 bne _syscall_exit_work
192 ;; this epilogue MUST match the prologues in multiple_interrupt, irq.h and ptregs.h
194 bne _RBFexit ; was not CRIS_FRAME_NORMAL, handle otherwise
195 addq 4, $sp ; skip orig_r10, in delayslot
196 movem [$sp+], $r13 ; registers r0-r13
197 pop $mof ; multiply overflow register
198 pop $dccr ; condition codes
199 pop $srp ; subroutine return pointer
200 ;; now we have a 4-word SBFS frame which we do not want to restore
201 ;; using RBF since it was not stacked with SBFS. instead we would like to
202 ;; just get the PC value to restart it with, and skip the rest of
204 ;; Also notice that it's important to use instructions here that
205 ;; keep the interrupts disabled (since we've already popped DCCR)
206 move [$sp=$sp+16], $p8; pop the SBFS frame from the sp
207 jmpu [$sp-16] ; return through the irp field in the sbfs frame
210 movem [$sp+], $r13 ; registers r0-r13, in delay slot
211 pop $mof ; multiply overflow register
212 pop $dccr ; condition codes
213 pop $srp ; subroutine return pointer
214 rbf [$sp+] ; return by popping the CPU status
216 ;; We get here after doing a syscall if extra work might need to be done
217 ;; perform syscall exit tracing if needed
220 ;; $r0 contains current at this point and irq's are disabled
222 move.d [$r0+TI_flags], $r1
223 btstq TIF_SYSCALL_TRACE, $r1
229 move.d $r9, $r1 ; preserve r9
237 move.d [$r0+TI_flags], $r1
238 btstq TIF_NEED_RESCHED, $r1
239 bpl _work_notifysig ; was neither trace nor sched, must be signal/notify
243 move.d $r9, $r1 ; preserve r9
248 move.d [$r0+TI_flags], $r1
249 and.d _TIF_WORK_MASK, $r1; ignore the syscall trace counter
252 btstq TIF_NEED_RESCHED, $r1
253 bmi _work_resched ; current->work.need_resched
257 ;; deal with pending signals and notify-resume requests
259 move.d $r9, $r10 ; do_notify_resume syscall/irq param
260 move.d $sp, $r11 ; the regs param
261 move.d $r1, $r12 ; the thread_info_flags parameter
267 ;; We get here as a sidetrack when we've entered a syscall with the
268 ;; trace-bit set. We need to call do_syscall_trace and then continue
271 _syscall_trace_entry:
272 ;; PT_r10 in the frame contains -ENOSYS as required, at this point
276 ;; now re-enter the syscall code to do the syscall itself
277 ;; we need to restore $r9 here to contain the wanted syscall, and
278 ;; the other parameter-bearing registers
280 move.d [$sp+PT_r9], $r9
281 move.d [$sp+PT_orig_r10], $r10 ; PT_r10 is already filled with -ENOSYS.
282 move.d [$sp+PT_r11], $r11
283 move.d [$sp+PT_r12], $r12
284 move.d [$sp+PT_r13], $r13
285 move [$sp+PT_mof], $mof
286 move [$sp+PT_srp], $srp
291 ;; resume performs the actual task-switching, by switching stack pointers
292 ;; input arguments: r10 = prev, r11 = next, r12 = thread offset in task struct
293 ;; returns old current in r10
295 ;; TODO: see the i386 version. The switch_to which calls resume in our version
296 ;; could really be an inline asm of this.
299 push $srp ; we keep the old/new PC on the stack
300 add.d $r12, $r10 ; r10 = current tasks tss
301 move $dccr, [$r10+THREAD_dccr]; save irq enable state
304 move $usp, [$r10+ THREAD_usp] ; save user-mode stackpointer
306 ;; See copy_thread for the reason why register R9 is saved.
308 movem $r9, [$sp] ; save non-scratch registers and R9.
310 move.d $sp, [$r10+THREAD_ksp] ; save the kernel stack pointer for the old task
311 move.d $sp, $r10 ; return last running task in r10
312 and.d -8192, $r10 ; get thread_info from stackpointer
313 move.d [$r10+TI_task], $r10 ; get task
314 add.d $r12, $r11 ; find the new tasks tss
315 move.d [$r11+THREAD_ksp], $sp ; switch into the new stackframe by restoring kernel sp
317 movem [$sp+], $r9 ; restore non-scratch registers and R9.
319 move [$r11+THREAD_usp], $usp ; restore user-mode stackpointer
321 move [$r11+THREAD_dccr], $dccr ; restore irq enable status
322 jump [$sp+] ; restore PC
324 ;; This is the MMU bus fault handler.
325 ;; It needs to stack the CPU status and overall is different
326 ;; from the other interrupt handlers.
329 ;; For refills we try to do a quick page table lookup. If it is
330 ;; a real fault we let the mm subsystem handle it.
332 ;; the first longword in the sbfs frame was the interrupted PC
333 ;; which fits nicely with the "IRP" slot in pt_regs normally used to
334 ;; contain the return address. used by Oops to print kernel errors.
335 sbfs [$sp=$sp-16] ; push the internal CPU status
340 move.d [R_MMU_CAUSE], $r1
341 ;; ETRAX 100LX TR89 bugfix: if the second half of an unaligned
342 ;; write causes a MMU-fault, it will not be restarted correctly.
343 ;; This could happen if a write crosses a page-boundary and the
344 ;; second page is not yet COW'ed or even loaded. The workaround
345 ;; is to clear the unaligned bit in the CPU status record, so
346 ;; that the CPU will rerun both the first and second halves of
347 ;; the instruction. This will not have any sideeffects unless
348 ;; the first half goes to any device or memory that can't be
349 ;; written twice, and which is mapped through the MMU.
351 ;; We only need to do this for writes.
352 btstq 8, $r1 ; Write access?
355 move.d [$sp+16], $r0 ; Clear unaligned bit in csrinstr
358 1: btstq 12, $r1 ; Refill?
360 lsrq 24, $r1 ; Get PGD index (bit 24-31)
361 move.d [per_cpu__current_pgd], $r0 ; PGD for the current process
362 move.d [$r0+$r1.d], $r0 ; Get PMD
365 and.w PAGE_MASK, $r0 ; Remove PMD flags
366 move.d [R_MMU_CAUSE], $r1
368 and.d 0x7ff, $r1 ; Get PTE index into PGD (bit 13-23)
369 move.d [$r0+$r1.d], $r1 ; Get PTE
373 move.d $r1, [R_TLB_LO]
377 rbf [$sp+] ; return by popping the CPU status
379 2: ; PMD or PTE missing, let the mm subsystem fix it up.
383 ; Ok, not that easy, pass it on to the mm subsystem
384 ; The MMU status record is now on the stack
385 push $srp ; make a stackframe similar to pt_regs
391 push $r10 ; dummy orig_r10
393 push $r10 ; frametype == 1, BUSFAULT frame type
395 move.d $sp, $r10 ; pt_regs argument to handle_mmu_bus_fault
397 jsr handle_mmu_bus_fault ; in arch/cris/arch-v10/mm/fault.c
399 ;; now we need to return through the normal path, we cannot just
400 ;; do the RBFexit since we might have killed off the running
401 ;; process due to a SEGV, scheduled due to a page blocking or
404 moveq 0, $r9 ; busfault is equivalent to an irq
409 ;; special handlers for breakpoint and NMI
415 move.d [hw_bp_trig_ptr],$r10
418 move.d $r10,[hw_bp_trig_ptr]
426 ;; this prologue MUST match the one in irq.h and the struct in ptregs.h!!!
427 move $brp,[$sp=$sp-16]; instruction pointer and room for a fake SBFS frame
434 push $r10 ; push orig_r10
435 clear.d [$sp=$sp-4] ; frametype == 0, normal frame
437 ;; If there is a glitch on the NMI pin shorter than ~100ns
438 ;; (i.e. non-active by the time we get here) then the nmi_pin bit
439 ;; in R_IRQ_MASK0_RD will already be cleared. The watchdog_nmi bit
440 ;; is cleared by us however (when feeding the watchdog), which is why
441 ;; we use that bit to determine what brought us here.
443 move.d [R_IRQ_MASK0_RD], $r1 ; External NMI or watchdog?
448 setf m ; Enable NMI again
449 ba _Rexit ; Return the standard way
452 #if defined(CONFIG_ETRAX_WATCHDOG) && !defined(CONFIG_SVINTO_SIM)
453 ;; Check if we're waiting for reset to happen, as signalled by
454 ;; hard_reset_now setting cause_of_death to a magic value. If so, just
455 ;; get stuck until reset happens.
456 .comm cause_of_death, 4 ;; Don't declare this anywhere.
457 move.d [cause_of_death], $r10
463 ;; We'll see this in ksymoops dumps.
466 #ifdef CONFIG_ETRAX_WATCHDOG_NICE_DOGGY
467 ;; We just restart the watchdog here to be sure we dont get
468 ;; hit while printing the watchdogmsg below
469 ;; This restart is compatible with the rest of the C-code, so
470 ;; the C-code can keep restarting the watchdog after this point.
471 ;; The non-NICE_DOGGY code below though, disables the possibility
472 ;; to restart since it changes the watchdog key, to avoid any
473 ;; buggy loops etc. keeping the watchdog alive after this.
477 ;; We need to extend the 3.3ms after the NMI at watchdog bite, so we have
478 ;; time for an oops-dump over a 115k2 serial wire. Another 100ms should do.
480 ;; Change the watchdog key to an arbitrary 3-bit value and restart the
483 moveq IO_FIELD (R_WATCHDOG, key, WD_INIT), $r10
484 move.d R_WATCHDOG, $r11
487 moveq IO_FIELD (R_WATCHDOG, key, \
488 IO_EXTRACT (R_WATCHDOG, key, \
489 IO_MASK (R_WATCHDOG, key)) \
491 | IO_STATE (R_WATCHDOG, enable, start), $r10
496 ;; Note that we don't do "setf m" here (or after two necessary NOPs),
497 ;; since *not* doing that saves us from re-entrancy checks. We don't want
498 ;; to get here again due to possible subsequent NMIs; we want the watchdog
501 move.d _watchdogmsg,$r10
505 jsr watchdog_bite_hook
507 ;; This nop is here so we see the "Watchdog_bite" label in ksymoops dumps
508 ;; rather than "spurious_interrupt".
510 ;; At this point we drop down into spurious_interrupt, which will do a
515 .ascii "Oops: bitten by watchdog\n\0"
518 #endif /* CONFIG_ETRAX_WATCHDOG and not CONFIG_SVINTO_SIM */
524 ;; this handles the case when multiple interrupts arrive at the same time
525 ;; we jump to the first set interrupt bit in a priority fashion
526 ;; the hardware will call the unserved interrupts after the handler finishes
529 ;; this prologue MUST match the one in irq.h and the struct in ptregs.h!!!
530 move $irp,[$sp=$sp-16]; instruction pointer and room for a fake SBFS frame
537 push $r10 ; push orig_r10
538 clear.d [$sp=$sp-4] ; frametype == 0, normal frame
547 ;; SIGTRAP the process that executed the break instruction.
548 ;; Make a frame that Rexit in entry.S expects.
550 move $brp, [$sp=$sp-16] ; Push BRP while faking a cpu status record.
551 push $srp ; Push subroutine return pointer.
552 push $dccr ; Push condition codes.
553 push $mof ; Push multiply overflow reg.
554 di ; Need to disable irq's at this point.
555 subq 14*4, $sp ; Make room for r0-r13.
556 movem $r13, [$sp] ; Push the r0-r13 registers.
557 push $r10 ; Push orig_r10.
558 clear.d [$sp=$sp-4] ; Frametype - this is a normal stackframe.
560 movs.w -8192,$r9 ; THREAD_SIZE == 8192
562 move.d [$r9+TI_task], $r10
563 move.d [$r10+TASK_pid], $r10 ; current->pid as arg1.
564 moveq 5, $r11 ; SIGTRAP as arg2.
566 jump ret_from_intr ; Use the return routine for interrupts.
568 gdb_handle_breakpoint:
571 #ifdef CONFIG_ETRAX_KGDB
572 move $dccr, $r0 ; U-flag not affected by previous insns.
573 btstq 8, $r0 ; Test the U-flag.
574 bmi _ugdb_handle_breakpoint ; Go to user mode debugging.
575 nop ; Empty delay slot (cannot pop r0 here).
576 pop $r0 ; Restore r0.
577 ba kgdb_handle_breakpoint ; Go to kernel debugging.
578 pop $dccr ; Restore dccr in delay slot.
581 _ugdb_handle_breakpoint:
582 move $brp, $r0 ; Use r0 temporarily for calculation.
583 subq 2, $r0 ; Set to address of previous instruction.
585 pop $r0 ; Restore r0.
586 ba do_sigtrap ; SIGTRAP the offending process.
587 pop $dccr ; Restore dccr in delay slot.
589 .global kernel_execve
591 move.d __NR_execve, $r9
605 .long sys_restart_syscall /* 0 - old "setup()" system call, used for restarting */
610 .long sys_open /* 5 */
615 .long sys_unlink /* 10 */
620 .long sys_chmod /* 15 */
622 .long sys_ni_syscall /* old break syscall holder */
625 .long sys_getpid /* 20 */
630 .long sys_stime /* 25 */
635 .long sys_utime /* 30 */
636 .long sys_ni_syscall /* old stty syscall holder */
637 .long sys_ni_syscall /* old gtty syscall holder */
640 .long sys_ni_syscall /* 35 old ftime syscall holder */
645 .long sys_rmdir /* 40 */
649 .long sys_ni_syscall /* old prof syscall holder */
650 .long sys_brk /* 45 */
655 .long sys_getegid16 /* 50 */
657 .long sys_umount /* recycled never used phys( */
658 .long sys_ni_syscall /* old lock syscall holder */
660 .long sys_fcntl /* 55 */
661 .long sys_ni_syscall /* old mpx syscall holder */
663 .long sys_ni_syscall /* old ulimit syscall holder */
664 .long sys_ni_syscall /* old sys_olduname holder */
665 .long sys_umask /* 60 */
670 .long sys_getpgrp /* 65 */
675 .long sys_setreuid16 /* 70 */
679 .long sys_sethostname
680 .long sys_setrlimit /* 75 */
681 .long sys_old_getrlimit
683 .long sys_gettimeofday
684 .long sys_settimeofday
685 .long sys_getgroups16 /* 80 */
686 .long sys_setgroups16
687 .long sys_select /* was old_select in Linux/E100 */
690 .long sys_readlink /* 85 */
695 .long old_mmap /* 90 */
700 .long sys_fchown16 /* 95 */
701 .long sys_getpriority
702 .long sys_setpriority
703 .long sys_ni_syscall /* old profil syscall holder */
705 .long sys_fstatfs /* 100 */
706 .long sys_ni_syscall /* sys_ioperm in i386 */
710 .long sys_getitimer /* 105 */
714 .long sys_ni_syscall /* old sys_uname holder */
715 .long sys_ni_syscall /* sys_iopl in i386 */
717 .long sys_ni_syscall /* old "idle" system call */
718 .long sys_ni_syscall /* vm86old in i386 */
720 .long sys_swapoff /* 115 */
725 .long sys_clone /* 120 */
726 .long sys_setdomainname
728 .long sys_ni_syscall /* sys_modify_ldt */
730 .long sys_mprotect /* 125 */
731 .long sys_sigprocmask
732 .long sys_ni_syscall /* old "create_module" */
733 .long sys_init_module
734 .long sys_delete_module
735 .long sys_ni_syscall /* 130: old "get_kernel_syms" */
740 .long sys_sysfs /* 135 */
741 .long sys_personality
742 .long sys_ni_syscall /* for afs_syscall */
745 .long sys_llseek /* 140 */
750 .long sys_readv /* 145 */
755 .long sys_mlock /* 150 */
759 .long sys_sched_setparam
760 .long sys_sched_getparam /* 155 */
761 .long sys_sched_setscheduler
762 .long sys_sched_getscheduler
763 .long sys_sched_yield
764 .long sys_sched_get_priority_max
765 .long sys_sched_get_priority_min /* 160 */
766 .long sys_sched_rr_get_interval
769 .long sys_setresuid16
770 .long sys_getresuid16 /* 165 */
771 .long sys_ni_syscall /* sys_vm86 */
772 .long sys_ni_syscall /* Old sys_query_module */
775 .long sys_setresgid16 /* 170 */
776 .long sys_getresgid16
778 .long sys_rt_sigreturn
779 .long sys_rt_sigaction
780 .long sys_rt_sigprocmask /* 175 */
781 .long sys_rt_sigpending
782 .long sys_rt_sigtimedwait
783 .long sys_rt_sigqueueinfo
784 .long sys_rt_sigsuspend
785 .long sys_pread64 /* 180 */
790 .long sys_capset /* 185 */
791 .long sys_sigaltstack
793 .long sys_ni_syscall /* streams1 */
794 .long sys_ni_syscall /* streams2 */
795 .long sys_vfork /* 190 */
799 .long sys_ftruncate64
800 .long sys_stat64 /* 195 */
805 .long sys_getgid /* 200 */
810 .long sys_getgroups /* 205 */
815 .long sys_setresgid /* 210 */
820 .long sys_setfsuid /* 215 */
825 .long sys_getdents64 /* 220 */
827 .long sys_ni_syscall /* reserved for TUX */
830 .long sys_readahead /* 225 */
835 .long sys_lgetxattr /* 230 */
840 .long sys_removexattr /* 235 */
841 .long sys_lremovexattr
842 .long sys_fremovexattr
845 .long sys_futex /* 240 */
846 .long sys_sched_setaffinity
847 .long sys_sched_getaffinity
848 .long sys_ni_syscall /* sys_set_thread_area */
849 .long sys_ni_syscall /* sys_get_thread_area */
850 .long sys_io_setup /* 245 */
852 .long sys_io_getevents
855 .long sys_fadvise64 /* 250 */
858 .long sys_lookup_dcookie
859 .long sys_epoll_create
860 .long sys_epoll_ctl /* 255 */
862 .long sys_remap_file_pages
863 .long sys_set_tid_address
864 .long sys_timer_create
865 .long sys_timer_settime /* 260 */
866 .long sys_timer_gettime
867 .long sys_timer_getoverrun
868 .long sys_timer_delete
869 .long sys_clock_settime
870 .long sys_clock_gettime /* 265 */
871 .long sys_clock_getres
872 .long sys_clock_nanosleep
875 .long sys_tgkill /* 270 */
877 .long sys_fadvise64_64
878 .long sys_ni_syscall /* sys_vserver */
879 .long sys_ni_syscall /* sys_mbind */
880 .long sys_ni_syscall /* 275 sys_get_mempolicy */
881 .long sys_ni_syscall /* sys_set_mempolicy */
884 .long sys_mq_timedsend
885 .long sys_mq_timedreceive /* 280 */
887 .long sys_mq_getsetattr
888 .long sys_ni_syscall /* reserved for kexec */
890 .long sys_ni_syscall /* 285 */ /* available */
892 .long sys_request_key
895 .long sys_ioprio_get /* 290 */
896 .long sys_inotify_init
897 .long sys_inotify_add_watch
898 .long sys_inotify_rm_watch
899 .long sys_migrate_pages
900 .long sys_openat /* 295 */
905 .long sys_fstatat64 /* 300 */
910 .long sys_readlinkat /* 305 */
915 .long sys_unshare /* 310 */
916 .long sys_set_robust_list
917 .long sys_get_robust_list
919 .long sys_sync_file_range
920 .long sys_tee /* 315 */
924 .long sys_epoll_pwait
925 .long sys_utimensat /* 320 */
927 .long sys_timerfd_create
930 .long sys_timerfd_settime /* 325 */
931 .long sys_timerfd_gettime
934 * NOTE!! This doesn't have to be exact - we just have
935 * to make sure we have _enough_ of the "sys_ni_syscall"
936 * entries. Don't panic if you notice that this hasn't
937 * been shrunk every time we add a new system call.
940 .rept NR_syscalls-(.-sys_call_table)/4