entry.s

LINUX 2.6.17.4的源码

   (via the function `switch_thread'), so callers will save any
   call-clobbered registers themselves.  We do need to save the CT regs, as
   they're normally not saved during kernel entry (the kernel doesn't use
   them).  We save PSW so that interrupt-status state will correctly follow
   each thread (mostly NMI vs. normal-IRQ/trap), though for the most part
   it doesn't matter since threads are always in almost exactly the same
   processor state during a context switch.  The stack pointer and return
   value are handled by switch_thread itself.  */
#define SWITCH_STATE_SAVER						      \
	SAVE_CALL_SAVED_REGS;						      \
	SAVE_PSW(PSW);							      \
	SAVE_CT_REGS
#define SWITCH_STATE_RESTORER						      \
	RESTORE_CALL_SAVED_REGS;					      \
	RESTORE_PSW(PSW);						      \
	RESTORE_CT_REGS


/* Restore register state from the state-save-frame on the stack, switch back
   to the user stack if necessary, and return from the trap/interrupt.
   EXTRA_STATE_RESTORER is a sequence of assembly language statements to
   restore anything not restored by this macro.  Only registers not saved by
   the C compiler are restored (that is, R3(sp), R4(gp), R31(lp), and
   anything restored by EXTRA_STATE_RESTORER).  */
#define RETURN(type)							      \
	ld.b	PTO+PT_KERNEL_MODE[sp], r19;				      \
	di;				/* Disable interrupts */	      \
	cmp	r19, r0;		/* See if returning to kernel mode, */\
	bne	2f;			/* ... if so, skip resched &c.  */    \
									      \
	/* We're returning to user mode, so check for various conditions that \
	   trigger rescheduling. */					      \
	GET_CURRENT_THREAD(r18);					      \
	ld.w	TI_FLAGS[r18], r19;					      \
	andi	_TIF_NEED_RESCHED, r19, r0;				      \
	bnz	3f;			/* Call the scheduler.  */	      \
5:	andi	_TIF_SIGPENDING, r19, r18;				      \
	ld.w	TASK_PTRACE[CURRENT_TASK], r19; /* ptrace flags */	      \
	or	r18, r19;		/* see if either is non-zero */	      \
	bnz	4f;			/* if so, handle them */	      \
									      \
/* Return to user state.  */						      \
1:	st.b	r0, KM;			/* Now officially in user state. */   \
									      \
/* Final return.  The stack-pointer fiddling is not needed when returning     \
   to kernel-mode, but they don't hurt, and this way we can share the	      \
   (sometimes rather lengthy) POP_STATE macro.  */			      \
2:	POP_STATE(type);						      \
	st.w	sp, KSP;		/* Save the kernel stack pointer. */  \
	ld.w	PT_GPR(GPR_SP)-PT_SIZE[sp], sp; /* Restore stack pointer. */  \
	type ## _RET;			/* Return from the trap/interrupt. */ \
									      \
/* Call the scheduler before returning from a syscall/trap. */		      \
3:	SAVE_EXTRA_STATE_FOR_SCHEDULE(type); /* Prepare to call scheduler. */ \
	jarl	call_scheduler, lp;	/* Call scheduler */		      \
	di;				/* The scheduler enables interrupts */\
	RESTORE_EXTRA_STATE_FOR_SCHEDULE(type);				      \
	GET_CURRENT_THREAD(r18);					      \
	ld.w	TI_FLAGS[r18], r19;					      \
	br	5b;			/* Continue with return path. */      \
									      \
/* Handle a signal or ptraced process return.				      \
   r18 should be non-zero if there are pending signals.  */		      \
4:	/* Not all registers are saved by the normal trap/interrupt entry     \
	   points (for instance, call-saved registers (because the normal     \
	   C-compiler calling sequence in the kernel makes sure they're	      \
	   preserved), and call-clobbered registers in the case of	      \
	   traps), but signal handlers may want to examine or change the      \
	   complete register state.  Here we save anything not saved by	      \
	   the normal entry sequence, so that it may be safely restored	      \
	   (in a possibly modified form) after do_signal returns.  */	      \
	SAVE_EXTRA_STATE(type);		/* Save state not saved by entry. */  \
	jarl	handle_signal_or_ptrace_return, lp;			      \
	RESTORE_EXTRA_STATE(type);	/* Restore extra regs.  */	      \
	br	1b


/* Jump to the appropriate function for the system call number in r12
   (r12 is not preserved), or return an error if r12 is not valid.  The
   LP register should point to the location where the called function
   should return.  [note that MAKE_SYS_CALL uses label 1]  */
#define MAKE_SYS_CALL							      \
	/* Figure out which function to use for this system call.  */	      \
	shl	2, r12;							      \
	/* See if the system call number is valid.  */			      \
	addi	lo(CSYM(sys_call_table) - sys_call_table_end), r12, r0;	      \
	bnh	1f;							      \
	mov	hilo(CSYM(sys_call_table)), r19;			      \
	add	r19, r12;						      \
	ld.w	0[r12], r12;						      \
	/* Make the system call.  */					      \
	jmp	[r12];							      \
	/* The syscall number is invalid, return an error.  */		      \
1:	addi	-ENOSYS, r0, r10;					      \
	jmp	[lp]


	.text

/*
 * User trap.
 *
 * Trap 0 system calls are also handled here.
 *
 * The stack-pointer (r3) should have already been saved to the memory
 * location ENTRY_SP (the reason for this is that the interrupt vectors may be
 * beyond a 22-bit signed offset jump from the actual interrupt handler, and
 * this allows them to save the stack-pointer and use that register to do an
 * indirect jump).
 *
 * Syscall protocol:
 *   Syscall number in r12, args in r6-r9
 *   Return value in r10
 */
G_ENTRY(trap):
	SAVE_STATE (TRAP, r12, ENTRY_SP) // Save registers.
	stsr	SR_ECR, r19		// Find out which trap it was.
	ei				// Enable interrupts.
	mov	hilo(ret_from_trap), lp	// where the trap should return

	// The following two shifts (1) clear out extraneous NMI data in the
	// upper 16-bits, (2) convert the 0x40 - 0x5f range of trap ECR
	// numbers into the (0-31) << 2 range we want, (3) set the flags.
	shl	27, r19			// chop off all high bits
	shr	25, r19			// scale back down and then << 2
	bnz	2f			// See if not trap 0.

	// Trap 0 is a `short' system call, skip general trap table.
	MAKE_SYS_CALL			// Jump to the syscall function.

2:	// For other traps, use a table lookup.
	mov	hilo(CSYM(trap_table)), r18
	add	r19, r18
	ld.w	0[r18], r18
	jmp	[r18]			// Jump to the trap handler.
END(trap)

/* This is just like ret_from_trap, but first restores extra registers
   saved by some wrappers.  */
L_ENTRY(restore_extra_regs_and_ret_from_trap):
	RESTORE_EXTRA_STATE(TRAP)
	// fall through
END(restore_extra_regs_and_ret_from_trap)

/* Entry point used to return from a syscall/trap.  */
L_ENTRY(ret_from_trap):
	RETURN(TRAP)
END(ret_from_trap)


/* This the initial entry point for a new child thread, with an appropriate
   stack in place that makes it look the the child is in the middle of an
   syscall.  This function is actually `returned to' from switch_thread
   (copy_thread makes ret_from_fork the return address in each new thread's
   saved context).  */
C_ENTRY(ret_from_fork):
	mov	r10, r6			// switch_thread returns the prev task.
	jarl	CSYM(schedule_tail), lp	// ...which is schedule_tail's arg
	mov	r0, r10			// Child's fork call should return 0.
	br	ret_from_trap		// Do normal trap return.
C_END(ret_from_fork)


/*
 * Trap 1: `long' system calls
 * `Long' syscall protocol:
 *   Syscall number in r12, args in r6-r9, r13-r14
 *   Return value in r10
 */
L_ENTRY(syscall_long):
	// Push extra arguments on the stack.  Note that by default, the trap
	// handler reserves enough stack space for 6 arguments, so we don't
	// have to make any additional room.
	st.w	r13, 16[sp]		// arg 5
	st.w	r14, 20[sp]		// arg 6

	// Make sure r13 and r14 are preserved, in case we have to restart a
	// system call because of a signal (ep has already been set by caller).
	st.w	r13, PTO+PT_GPR(13)[sp]
	st.w	r14, PTO+PT_GPR(13)[sp]
	mov	hilo(ret_from_long_syscall), lp

	MAKE_SYS_CALL			// Jump to the syscall function.
END(syscall_long)

/* Entry point used to return from a long syscall.  Only needed to restore
   r13/r14 if the general trap mechanism doesnt' do so.  */
L_ENTRY(ret_from_long_syscall):
	ld.w	PTO+PT_GPR(13)[sp], r13 // Restore the extra registers
	ld.w	PTO+PT_GPR(13)[sp], r14
	br	ret_from_trap		// The rest is the same as other traps
END(ret_from_long_syscall)


/* These syscalls need access to the struct pt_regs on the stack, so we
   implement them in assembly (they're basically all wrappers anyway).  */

L_ENTRY(sys_fork_wrapper):
#ifdef CONFIG_MMU
	addi	SIGCHLD, r0, r6		   // Arg 0: flags
	ld.w	PTO+PT_GPR(GPR_SP)[sp], r7 // Arg 1: child SP (use parent's)
	movea	PTO, sp, r8		   // Arg 2: parent context
	mov	r0, r9			   // Arg 3/4/5: 0
	st.w	r0, 16[sp]
	st.w	r0, 20[sp]
	mov	hilo(CSYM(do_fork)), r18   // Where the real work gets done
	br	save_extra_state_tramp	   // Save state and go there
#else
	// fork almost works, enough to trick you into looking elsewhere :-(
	addi	-EINVAL, r0, r10
	jmp	[lp]
#endif
END(sys_fork_wrapper)

L_ENTRY(sys_vfork_wrapper):
	addi	CLONE_VFORK | CLONE_VM | SIGCHLD, r0, r6 // Arg 0: flags
	ld.w	PTO+PT_GPR(GPR_SP)[sp], r7 // Arg 1: child SP (use parent's)
	movea	PTO, sp, r8		   // Arg 2: parent context
	mov	r0, r9			   // Arg 3/4/5: 0
	st.w	r0, 16[sp]
	st.w	r0, 20[sp]
	mov	hilo(CSYM(do_fork)), r18   // Where the real work gets done
	br	save_extra_state_tramp	   // Save state and go there
END(sys_vfork_wrapper)

L_ENTRY(sys_clone_wrapper):
	ld.w	PTO+PT_GPR(GPR_SP)[sp], r19// parent's stack pointer
	cmp	r7, r0			   // See if child SP arg (arg 1) is 0.
	cmov	z, r19, r7, r7		   // ... and use the parent's if so.
	movea	PTO, sp, r8		   // Arg 2: parent context
	mov	r0, r9			   // Arg 3/4/5: 0
	st.w	r0, 16[sp]
	st.w	r0, 20[sp]
	mov	hilo(CSYM(do_fork)), r18   // Where the real work gets done
	br	save_extra_state_tramp	   // Save state and go there
END(sys_clone_wrapper)


L_ENTRY(sys_execve_wrapper):
	movea	PTO, sp, r9		// add user context as 4th arg
	jr	CSYM(sys_execve)	// Do real work (tail-call).
END(sys_execve_wrapper)


L_ENTRY(sys_sigsuspend_wrapper):
	movea	PTO, sp, r7		// add user context as 2nd arg
	mov	hilo(CSYM(sys_sigsuspend)), r18	// syscall function
	jarl	save_extra_state_tramp, lp	// Save state and do it
	br	restore_extra_regs_and_ret_from_trap
END(sys_sigsuspend_wrapper)
L_ENTRY(sys_rt_sigsuspend_wrapper):
	movea	PTO, sp, r8		// add user context as 3rd arg
	mov	hilo(CSYM(sys_rt_sigsuspend)), r18 // syscall function
	jarl	save_extra_state_tramp, lp	   // Save state and do it
	br	restore_extra_regs_and_ret_from_trap
END(sys_rt_sigsuspend_wrapper)

L_ENTRY(sys_sigreturn_wrapper):
	movea	PTO, sp, r6		// add user context as 1st arg
	mov	hilo(CSYM(sys_sigreturn)), r18	// syscall function
	jarl	save_extra_state_tramp, lp	// Save state and do it
	br	restore_extra_regs_and_ret_from_trap
END(sys_sigreturn_wrapper)
L_ENTRY(sys_rt_sigreturn_wrapper):
	movea	PTO, sp, r6		// add user context as 1st arg
	mov	hilo(CSYM(sys_rt_sigreturn)), r18// syscall function
	jarl	save_extra_state_tramp, lp	 // Save state and do it
	br	restore_extra_regs_and_ret_from_trap
END(sys_rt_sigreturn_wrapper)


/* Save any state not saved by SAVE_STATE(TRAP), and jump to r18.
   It's main purpose is to share the rather lengthy code sequence that
   SAVE_STATE expands into among the above wrapper functions.  */
L_ENTRY(save_extra_state_tramp):
	SAVE_EXTRA_STATE(TRAP)		// Save state not saved by entry.
	jmp	[r18]			// Do the work the caller wants
END(save_extra_state_tramp)


/*
 * Hardware maskable interrupts.
 *
 * The stack-pointer (r3) should have already been saved to the memory
 * location ENTRY_SP (the reason for this is that the interrupt vectors may be
 * beyond a 22-bit signed offset jump from the actual interrupt handler, and
 * this allows them to save the stack-pointer and use that register to do an
 * indirect jump).
 */
G_ENTRY(irq):
	SAVE_STATE (IRQ, r0, ENTRY_SP)	// Save registers.

	stsr	SR_ECR, r6		// Find out which interrupt it was.
	movea	PTO, sp, r7		// User regs are arg2

	// All v850 implementations I know about encode their interrupts as
	// multiples of 0x10, starting at 0x80 (after NMIs and software
	// interrupts).  Convert this number into a simple IRQ index for the
	// rest of the kernel.  We also clear the upper 16 bits, which hold
	// NMI info, and don't appear to be cleared when a NMI returns.
	shl	16, r6			// clear upper 16 bits
	shr	20, r6			// shift back, and remove lower nibble
	add	-8, r6			// remove bias for irqs

	// Call the high-level interrupt handling code.
	jarl	CSYM(handle_irq), lp

	RETURN(IRQ)
END(irq)


/*
 * Debug trap / illegal-instruction exception
 *
 * The stack-pointer (r3) should have already been saved to the memory
 * location ENTRY_SP (the reason for this is that the interrupt vectors may be
 * beyond a 22-bit signed offset jump from the actual interrupt handler, and
 * this allows them to save the stack-pointer and use that register to do an
 * indirect jump).
 */
G_ENTRY(dbtrap):
	SAVE_STATE (DBTRAP, r0, ENTRY_SP)// Save registers.

	/* First see if we came from kernel mode; if so, the dbtrap
	   instruction has a special meaning, to set the DIR (`debug
	   information register') register.  This is because the DIR register
	   can _only_ be manipulated/read while in `debug mode,' and debug
	   mode is only active while we're inside the dbtrap handler.  The
	   exact functionality is:  { DIR = (DIR | r6) & ~r7; return DIR; }. */
	ld.b	PTO+PT_KERNEL_MODE[sp], r19
	cmp	r19, r0
	bz	1f

	stsr	SR_DIR, r10
	or	r6, r10
	not	r7, r7
	and	r7, r10
	ldsr	r10, SR_DIR
	stsr	SR_DIR, r10		// Confirm the value we set
	st.w	r10, PTO+PT_GPR(10)[sp]	// return it
	br	3f

1:	ei				// Enable interrupts.

	/* The default signal type we raise.  */
	mov	SIGTRAP, r6

	/* See if it's a single-step trap.  */
	stsr	SR_DBPSW, r19
	andi	0x0800, r19, r19
	bnz	2f

	/* Look to see if the preceding instruction was is a dbtrap or not,
	   to decide which signal we should use.  */
	stsr	SR_DBPC, r19		// PC following trapping insn
	ld.hu	-2[r19], r19
	ori	0xf840, r0, r20		// DBTRAP insn
	cmp	r19, r20		// Was this trap caused by DBTRAP?
	cmov	ne, SIGILL, r6, r6	// Choose signal appropriately

	/* Raise the desired signal.  */
2:	mov	CURRENT_TASK, r7	// Arg 1: task
	jarl	CSYM(send_sig), lp	// tail call

3:	RETURN(DBTRAP)
END(dbtrap)


/*
 * Hardware non-maskable interrupts.
 *
 * The stack-pointer (r3) should have already been saved to the memory
 * location ENTRY_SP (the reason for this is that the interrupt vectors may be
 * beyond a 22-bit signed offset jump from the actual interrupt handler, and