entry.s

linux内核源码

	cmpu.w	NR_syscalls, $r9	
	bcc	ret_from_sys_call
	lslq	2, $r9		;  multiply by 4, in the delay slot

	;; as a bonus 7th parameter, we give the location on the stack
	;; of the register structure itself. some syscalls need this.

	push	$sp
	
	;; the parameter carrying registers r10, r11, r12 and 13 are intact.
	;; the fifth and sixth parameters (if any) was in mof and srp 
	;; respectively, and we need to put them on the stack.

	push	$srp
	push	$mof
	
	jsr	[$r9+sys_call_table]	; actually do the system call
	addq	3*4, $sp		; pop the mof, srp and regs parameters
	move.d	$r10, [$sp+PT_r10]	; save the return value

	moveq	1, $r9		; "parameter" to ret_from_sys_call to show it was a sys call
	
	;; fall through into ret_from_sys_call to return
	
ret_from_sys_call:
	;; r9 is a parameter - if >=1 we came from a syscall, if 0, from an irq
		
	;; get the current task-struct pointer (see top for defs)

	movs.w	-8192, $r0	; THREAD_SIZE == 8192 
	and.d	$sp, $r0

	di			; make sure need_resched and sigpending don't change
	move.d	[$r0+TI_flags],$r1
	and.d	_TIF_ALLWORK_MASK, $r1
	bne	_syscall_exit_work
	nop

_Rexit:
	;; this epilogue MUST match the prologues in multiple_interrupt, irq.h and ptregs.h
	pop	$r10		; frametype
	bne	_RBFexit	; was not CRIS_FRAME_NORMAL, handle otherwise
	addq	4, $sp		; skip orig_r10, in delayslot
	movem	[$sp+], $r13	; registers r0-r13
	pop	$mof		; multiply overflow register 
	pop	$dccr		; condition codes
	pop	$srp		; subroutine return pointer
	;; now we have a 4-word SBFS frame which we do not want to restore
	;; using RBF since it was not stacked with SBFS. instead we would like to
	;; just get the PC value to restart it with, and skip the rest of
	;; the frame.
	;; Also notice that it's important to use instructions here that
	;; keep the interrupts disabled (since we've already popped DCCR)
	move	[$sp=$sp+16], $p8; pop the SBFS frame from the sp
	jmpu	[$sp-16]	; return through the irp field in the sbfs frame

_RBFexit:
	movem	[$sp+], $r13	; registers r0-r13, in delay slot
	pop	$mof		; multiply overflow register 
	pop	$dccr		; condition codes
	pop	$srp		; subroutine return pointer
	rbf	[$sp+]		; return by popping the CPU status

	;; We get here after doing a syscall if extra work might need to be done
	;; perform syscall exit tracing if needed
	
_syscall_exit_work:
	;; $r0 contains current at this point and irq's are disabled

	move.d  [$r0+TI_flags], $r1
	btstq	TIF_SYSCALL_TRACE, $r1
	bpl	_work_pending
	nop
	
	ei

	move.d	$r9, $r1	; preserve r9
	jsr	do_syscall_trace
	move.d	$r1, $r9
	
	ba	_resume_userspace
	nop
	
_work_pending:
	move.d  [$r0+TI_flags], $r1
	btstq   TIF_NEED_RESCHED, $r1
	bpl	_work_notifysig	; was neither trace nor sched, must be signal/notify
	nop
	
_work_resched:
	move.d	$r9, $r1	; preserve r9
	jsr	schedule
	move.d	$r1, $r9
	di

	move.d	[$r0+TI_flags], $r1
	and.d	_TIF_WORK_MASK, $r1; ignore the syscall trace counter
	beq	_Rexit
	nop
	btstq	TIF_NEED_RESCHED, $r1
	bmi	_work_resched	; current->work.need_resched
	nop

_work_notifysig:
	;; deal with pending signals and notify-resume requests

	move.d	$r9, $r10	; do_notify_resume syscall/irq param
	move.d	$sp, $r11	; the regs param
	move.d  $r1, $r12	; the thread_info_flags parameter
	jsr	do_notify_resume
	
	ba _Rexit
	nop

	;; We get here as a sidetrack when we've entered a syscall with the
	;; trace-bit set. We need to call do_syscall_trace and then continue
	;; with the call.
	
_syscall_trace_entry:
	;; PT_r10 in the frame contains -ENOSYS as required, at this point
	
	jsr	do_syscall_trace

	;; now re-enter the syscall code to do the syscall itself
	;; we need to restore $r9 here to contain the wanted syscall, and
	;; the other parameter-bearing registers

	move.d	[$sp+PT_r9], $r9
	move.d	[$sp+PT_orig_r10], $r10  ; PT_r10 is already filled with -ENOSYS.
	move.d	[$sp+PT_r11],      $r11
	move.d	[$sp+PT_r12],      $r12
	move.d	[$sp+PT_r13],      $r13
	move	[$sp+PT_mof],      $mof
	move	[$sp+PT_srp],      $srp
	
	ba	_syscall_traced
	nop
	
	;; resume performs the actual task-switching, by switching stack pointers
	;; input arguments: r10 = prev, r11 = next, r12 = thread offset in task struct
	;; returns old current in r10
	;;
	;; TODO:  see the i386 version. The switch_to which calls resume in our version
	;;        could really be an inline asm of this.

resume:	
	push	$srp		         ; we keep the old/new PC on the stack 
	add.d	$r12, $r10		 ; r10 = current tasks tss
	move	$dccr, [$r10+THREAD_dccr]; save irq enable state
	di

	move	$usp, [$r10+ THREAD_usp] ; save user-mode stackpointer
	
	;; See copy_thread for the reason why register R9 is saved.
	subq	10*4, $sp
	movem	$r9, [$sp]		 ; save non-scratch registers and R9.
	
	move.d	$sp, [$r10+THREAD_ksp]	 ; save the kernel stack pointer for the old task
	move.d	$sp, $r10		 ; return last running task in r10
	and.d   -8192, $r10	         ; get thread_info from stackpointer
	move.d  [$r10+TI_task], $r10     ; get task  
	add.d	$r12, $r11		 ; find the new tasks tss
	move.d	[$r11+THREAD_ksp], $sp	 ; switch into the new stackframe by restoring kernel sp

	movem	[$sp+], $r9		 ; restore non-scratch registers and R9.

	move	[$r11+THREAD_usp], $usp ; restore user-mode stackpointer
	
	move	[$r11+THREAD_dccr], $dccr ; restore irq enable status
	jump	[$sp+]		         ; restore PC

	;; This is the MMU bus fault handler.
	;; It needs to stack the CPU status and overall is different
	;; from the other interrupt handlers.

mmu_bus_fault:
	;; For refills we try to do a quick page table lookup. If it is
	;; a real fault we let the mm subsystem handle it.

	;; the first longword in the sbfs frame was the interrupted PC
	;; which fits nicely with the "IRP" slot in pt_regs normally used to
	;; contain the return address. used by Oops to print kernel errors.
	sbfs	[$sp=$sp-16]	; push the internal CPU status
	push	$dccr
	di
	subq	2*4, $sp
	movem	$r1, [$sp]
	move.d  [R_MMU_CAUSE], $r1
	;; ETRAX 100LX TR89 bugfix: if the second half of an unaligned
	;; write causes a MMU-fault, it will not be restarted correctly.
	;; This could happen if a write crosses a page-boundary and the
	;; second page is not yet COW'ed or even loaded. The workaround
	;; is to clear the unaligned bit in the CPU status record, so
	;; that the CPU will rerun both the first and second halves of
	;; the instruction. This will not have any sideeffects unless
	;; the first half goes to any device or memory that can't be
	;; written twice, and which is mapped through the MMU.
	;;
	;; We only need to do this for writes.
	btstq	8, $r1		   ; Write access?
	bpl	1f
	nop
	move.d	[$sp+16], $r0	   ; Clear unaligned bit in csrinstr
	and.d	~(1<<5), $r0
	move.d	$r0, [$sp+16]
1:	btstq	12, $r1		   ; Refill?
	bpl	2f
	lsrq	24, $r1     ; Get PGD index (bit 24-31)
	move.d  [per_cpu__current_pgd], $r0 ; PGD for the current process
	move.d	[$r0+$r1.d], $r0   ; Get PMD
	beq	2f
	nop
	and.w	PAGE_MASK, $r0	   ; Remove PMD flags
	move.d  [R_MMU_CAUSE], $r1
	lsrq	PAGE_SHIFT, $r1
	and.d	0x7ff, $r1         ; Get PTE index into PGD (bit 13-23)
	move.d	[$r0+$r1.d], $r1   ; Get PTE
	beq	2f
	nop
	;; Store in TLB
	move.d  $r1, [R_TLB_LO]
	;; Return
	movem	[$sp+], $r1
	pop	$dccr
	rbf	[$sp+]		; return by popping the CPU status

2:	; PMD or PTE missing, let the mm subsystem fix it up.
	movem	[$sp+], $r1
	pop	$dccr

	; Ok, not that easy, pass it on to the mm subsystem
	; The MMU status record is now on the stack
	push	$srp		; make a stackframe similar to pt_regs
	push	$dccr
	push	$mof
	di
	subq	14*4, $sp
	movem	$r13, [$sp]
	push	$r10		; dummy orig_r10
	moveq	1, $r10
	push	$r10		; frametype == 1, BUSFAULT frame type

	move.d	$sp, $r10	; pt_regs argument to handle_mmu_bus_fault
		
	jsr	handle_mmu_bus_fault  ; in arch/cris/arch-v10/mm/fault.c

	;; now we need to return through the normal path, we cannot just
	;; do the RBFexit since we might have killed off the running
	;; process due to a SEGV, scheduled due to a page blocking or
	;; whatever.

	moveq	0, $r9		; busfault is equivalent to an irq
		
	ba	ret_from_intr
	nop
		
	;; special handlers for breakpoint and NMI
hwbreakpoint:
	push	$dccr
	di
	push	$r10
	push	$r11
	move.d	[hw_bp_trig_ptr],$r10
	move	$brp,$r11
	move.d	$r11,[$r10+]
	move.d	$r10,[hw_bp_trig_ptr]
1:	pop	$r11
	pop	$r10
	pop	$dccr
	retb
	nop
	
IRQ1_interrupt:
	;; this prologue MUST match the one in irq.h and the struct in ptregs.h!!!
	move	$brp,[$sp=$sp-16]; instruction pointer and room for a fake SBFS frame
	push	$srp
	push	$dccr
	push	$mof
	di
	subq	14*4, $sp
	movem	$r13, [$sp]
	push	$r10		; push orig_r10
	clear.d [$sp=$sp-4]	; frametype == 0, normal frame

	;; If there is a glitch on the NMI pin shorter than ~100ns
	;; (i.e. non-active by the time we get here) then the nmi_pin bit
	;; in R_IRQ_MASK0_RD will already be cleared.  The watchdog_nmi bit
	;; is cleared by us however (when feeding the watchdog), which is why
	;; we use that bit to determine what brought us here.

	move.d	[R_IRQ_MASK0_RD], $r1 ; External NMI or watchdog?
	and.d   (1<<30), $r1
	bne	wdog
	move.d  $sp, $r10
	jsr	handle_nmi
	setf m			; Enable NMI again
	ba	_Rexit		; Return the standard way
	nop
wdog:
#if defined(CONFIG_ETRAX_WATCHDOG) && !defined(CONFIG_SVINTO_SIM)
;; Check if we're waiting for reset to happen, as signalled by
;; hard_reset_now setting cause_of_death to a magic value.  If so, just
;; get stuck until reset happens.
	.comm	cause_of_death, 4	;; Don't declare this anywhere.
	move.d	[cause_of_death], $r10
	cmp.d	0xbedead, $r10
_killed_by_death:
	beq	_killed_by_death
	nop

;; We'll see this in ksymoops dumps.
Watchdog_bite:

#ifdef CONFIG_ETRAX_WATCHDOG_NICE_DOGGY
       ;; We just restart the watchdog here to be sure we dont get
       ;; hit while printing the watchdogmsg below
       ;; This restart is compatible with the rest of the C-code, so
       ;; the C-code can keep restarting the watchdog after this point.
       ;; The non-NICE_DOGGY code below though, disables the possibility
       ;; to restart since it changes the watchdog key, to avoid any
       ;; buggy loops etc. keeping the watchdog alive after this.
       jsr     reset_watchdog
#else

;; We need to extend the 3.3ms after the NMI at watchdog bite, so we have
;; time for an oops-dump over a 115k2 serial wire.  Another 100ms should do.

;; Change the watchdog key to an arbitrary 3-bit value and restart the
;; watchdog.
#define WD_INIT 2
	moveq	  IO_FIELD (R_WATCHDOG, key, WD_INIT), $r10
	move.d	R_WATCHDOG, $r11

	move.d	$r10, [$r11]
	moveq	  IO_FIELD (R_WATCHDOG, key,				\
			    IO_EXTRACT (R_WATCHDOG, key,		\
					IO_MASK (R_WATCHDOG, key))	\
			    ^ WD_INIT)					\
		| IO_STATE (R_WATCHDOG, enable, start), $r10
	move.d	$r10, [$r11]

#endif
	
;; Note that we don't do "setf m" here (or after two necessary NOPs),
;; since *not* doing that saves us from re-entrancy checks.  We don't want
;; to get here again due to possible subsequent NMIs; we want the watchdog
;; to reset us.

	move.d	_watchdogmsg,$r10
	jsr	printk

	move.d	$sp, $r10
	jsr	watchdog_bite_hook

;; This nop is here so we see the "Watchdog_bite" label in ksymoops dumps
;; rather than "spurious_interrupt".
	nop
;; At this point we drop down into spurious_interrupt, which will do a
;; hard reset.

	.section .rodata,"a"
_watchdogmsg:
	.ascii	"Oops: bitten by watchdog\n\0"
	.previous

#endif /* CONFIG_ETRAX_WATCHDOG and not CONFIG_SVINTO_SIM */

spurious_interrupt:	
	di
	jump hard_reset_now

	;; this handles the case when multiple interrupts arrive at the same time
	;; we jump to the first set interrupt bit in a priority fashion
	;; the hardware will call the unserved interrupts after the handler finishes
	
multiple_interrupt:
	;; this prologue MUST match the one in irq.h and the struct in ptregs.h!!!
	move	$irp,[$sp=$sp-16]; instruction pointer and room for a fake SBFS frame
	push	$srp
	push	$dccr
	push	$mof
	di
	subq	14*4, $sp
	movem	$r13, [$sp]
	push	$r10		; push orig_r10
	clear.d [$sp=$sp-4]	; frametype == 0, normal frame
	
	move.d  $sp, $r10
	jsr	do_multiple_IRQ
	
	jump    ret_from_intr

do_sigtrap:
	;; 
	;; SIGTRAP the process that executed the break instruction.