locore.s

早期freebsd实现

	ld	[%l1 + %lo(_cpcb)], %l1
	st	%l0, [%l1 + PCB_WIM]	! cpcb->pcb_wim = cwp;
	save	%g0, %g0, %g0		! back to window I
	LOADWIN(%sp)
	save	%g0, %g0, %g0		! back to R
	save	%g0, %g0, %g0		! and then to T
	wr	%l0, 0, %psr		! fix those cond codes....
	nop				! (let them settle in)
	RETT

winuf_user:
	/*
	 * Underflow from user mode.
	 *
	 * We cannot use rft_user (as noted above) because
	 * we must re-execute the `restore' instruction.
	 * Since it could be, e.g., `restore %l0,0,%l0',
	 * it is not okay to touch R's registers either.
	 *
	 * We are now in window I.
	 */
	btst	7, %sp			! if unaligned, it is invalid
	bne	winuf_invalid
	 EMPTY

	PTE_OF_ADDR(%sp, %l7, winuf_invalid)
	CMP_PTE_USER_READ(%l7)		! if first page not readable,
	bne	winuf_invalid		! it is invalid
	 EMPTY
	SLT_IF_1PAGE_RW(%sp, %l7)	! first page is readable
	bl,a	winuf_ok		! if only one page, enter window X
	 restore %g0, 1, %l1		! and goto ok, & set %l1 to 1
	add	%sp, 7*8, %l5
	PTE_OF_ADDR(%l5, %l7, winuf_invalid)
	CMP_PTE_USER_READ(%l7)		! check second page too
	be,a	winuf_ok		! enter window X and goto ok
	 restore %g0, 1, %l1		! (and then set %l1 to 1)

winuf_invalid:
	/*
	 * We were unable to restore the window because %sp
	 * is invalid or paged out.  Return to the trap window
	 * and call trap(T_WINUF).  This will save R to the user
	 * stack, then load both R and I into the pcb rw[] area,
	 * and return with pcb_nsaved set to -1 for success, 0 for
	 * failure.  `Failure' indicates that someone goofed with the
	 * trap registers (e.g., signals), so that we need to return
	 * from the trap as from a syscall (probably to a signal handler)
	 * and let it retry the restore instruction later.  Note that
	 * window R will have been pushed out to user space, and thus
	 * be the invalid window, by the time we get back here.  (We
	 * continue to label it R anyway.)  We must also set %wim again,
	 * and set pcb_uw to 1, before enabling traps.  (Window R is the
	 * only window, and it is a user window).
	 */
	save	%g0, %g0, %g0		! back to R
#if 0		/* this gives `as' mild heartburn */
	save	%g0, 1, %l4		! back to T, then %l4 = 1
#else
	save	%g0, %g0, %g0		! back to T
	mov	1, %l4			! and set %l4 = 1
#endif
	sethi	%hi(_cpcb), %l6
	ld	[%l6 + %lo(_cpcb)], %l6
	st	%l4, [%l6 + PCB_UW]	! pcb_uw = 1
	ld	[%l6 + PCB_WIM], %l5	! get log2(%wim)
	sll	%l4, %l5, %l4		! %l4 = old %wim
	wr	%l4, 0, %wim		! window I is now invalid again
	set	UPAGES*NBPG-CCFSZ-80, %l5
	add	%l6, %l5, %sp		! get onto kernel stack
	CHECK_SP_REDZONE(%l6, %l5)

	/*
	 * Okay, call trap(T_WINUF, psr, pc, &tf).
	 * See `slowtrap' above for operation.
	 */
	wr	%l0, PSR_ET, %psr
	std	%l0, [%sp + CCFSZ + 0]	! tf.tf_psr, tf.tf_pc
	rd	%y, %l3
	std	%l2, [%sp + CCFSZ + 8]	! tf.tf_npc, tf.tf_y
	mov	T_WINUF, %o0
	st	%g1, [%sp + CCFSZ + 20]	! tf.tf_global[1]
	mov	%l0, %o1
	std	%g2, [%sp + CCFSZ + 24]	! etc
	mov	%l1, %o2
	std	%g4, [%sp + CCFSZ + 32]
	add	%sp, CCFSZ, %o3
	std	%g6, [%sp + CCFSZ + 40]
	std	%i0, [%sp + CCFSZ + 48]	! tf.tf_out[0], etc
	std	%i2, [%sp + CCFSZ + 56]
	std	%i4, [%sp + CCFSZ + 64]
	call	_trap			! trap(T_WINUF, pc, psr, &tf)
	 std	%i6, [%sp + CCFSZ + 72]	! tf.tf_out[6]

	ldd	[%sp + CCFSZ + 0], %l0	! new psr, pc
	ldd	[%sp + CCFSZ + 8], %l2	! new npc, %y
	wr	%l3, 0, %y
	ld	[%sp + CCFSZ + 20], %g1
	ldd	[%sp + CCFSZ + 24], %g2
	ldd	[%sp + CCFSZ + 32], %g4
	ldd	[%sp + CCFSZ + 40], %g6
	ldd	[%sp + CCFSZ + 48], %i0	! %o0 for window R, etc
	ldd	[%sp + CCFSZ + 56], %i2
	ldd	[%sp + CCFSZ + 64], %i4
	wr	%l0, 0, %psr		! disable traps: test must be atomic
	ldd	[%sp + CCFSZ + 72], %i6
	sethi	%hi(_cpcb), %l6
	ld	[%l6 + %lo(_cpcb)], %l6
	ld	[%l6 + PCB_NSAVED], %l7	! if nsaved is -1, we have our regs
	tst	%l7
	bl,a	1f			! got them
	 wr	%g0, 0, %wim		! allow us to enter windows R, I
	b,a	return_from_trap

	/*
	 * Got 'em.  Load 'em up.
	 */
1:
	mov	%g6, %l3		! save %g6; set %g6 = cpcb
	mov	%l6, %g6
	st	%g0, [%g6 + PCB_NSAVED]	! and clear magic flag
	restore				! from T to R
	restore				! from R to I
	restore	%g0, 1, %l1		! from I to X, then %l1 = 1
	rd	%psr, %l0		! cwp = %psr;
	sll	%l1, %l0, %l1
	wr	%l1, 0, %wim		! make window X invalid
	and	%l0, 31, %l0
	st	%l0, [%g6 + PCB_WIM]	! cpcb->pcb_wim = cwp;
	nop				! unnecessary? old wim was 0...
	save	%g0, %g0, %g0		! back to I
	LOADWIN(%g6 + PCB_RW + 64)	! load from rw[1]
	save	%g0, %g0, %g0		! back to R
	LOADWIN(%g6 + PCB_RW)		! load from rw[0]
	save	%g0, %g0, %g0		! back to T
	wr	%l0, 0, %psr		! restore condition codes
	mov	%l3, %g6		! fix %g6
	RETT

	/*
	 * Restoring from user stack, but everything has checked out
	 * as good.  We are now in window X, and %l1 = 1.  Window R
	 * is still valid and holds user values.
	 */
winuf_ok:
	rd	%psr, %l0
	sll	%l1, %l0, %l1
	wr	%l1, 0, %wim		! make this one invalid
	sethi	%hi(_cpcb), %l2
	ld	[%l2 + %lo(_cpcb)], %l2
	and	%l0, 31, %l0
	st	%l0, [%l2 + PCB_WIM]	! cpcb->pcb_wim = cwp;
	save	%g0, %g0, %g0		! back to I
	LOADWIN(%sp)
	save	%g0, %g0, %g0		! back to R
	save	%g0, %g0, %g0		! back to T
	wr	%l0, 0, %psr		! restore condition codes
	nop				! it takes three to tangle
	RETT
#endif /* end `real' version of window underflow trap handler */

/*
 * Various return-from-trap routines (see return_from_trap).
 */

/*
 * Return from trap, to kernel.
 *	%l0 = %psr
 *	%l1 = return pc
 *	%l2 = return npc
 *	%l4 = %wim
 *	%l5 = bit for previous window
 */
rft_kernel:
	btst	%l5, %l4		! if (wim & l5)
	bnz	1f			!	goto reload;
	 wr	%l0, 0, %psr		! but first put !@#*% cond codes back

	/* previous window is valid; just rett */
	nop				! wait for cond codes to settle in
	RETT

	/*
	 * Previous window is invalid.
	 * Update %wim and then reload l0..i7 from frame.
	 *
	 *	  T I X
	 *	0 0 1 0 0   (%wim)
	 * [see picture in window_uf handler]
	 *
	 * T is the current (Trap) window, I is the Invalid window,
	 * and X is the window we want to make invalid.  Window X
	 * currently has no useful values.
	 */
1:
	wr	%g0, 0, %wim		! allow us to enter window I
	nop; nop; nop			! (it takes a while)
	restore				! enter window I
	restore	%g0, 1, %l1		! enter window X, then %l1 = 1
	rd	%psr, %l0		! CWP = %psr & 31;
	and	%l0, 31, %l0
	sll	%l1, %l0, %l1		! wim = 1 << CWP;
	wr	%l1, 0, %wim		! setwim(wim);
	sethi	%hi(_cpcb), %l1
	ld	[%l1 + %lo(_cpcb)], %l1
	st	%l0, [%l1 + PCB_WIM]	! cpcb->pcb_wim = l0 & 31;
	save	%g0, %g0, %g0		! back to window I
	LOADWIN(%sp)
	save	%g0, %g0, %g0		! back to window T
	/*
	 * Note that the condition codes are still set from
	 * the code at rft_kernel; we can simply return.
	 */
	RETT

/*
 * Return from trap, to user.  Checks for scheduling trap (`ast') first;
 * will re-enter trap() if set.  Note that we may have to switch from
 * the interrupt stack to the kernel stack in this case.
 *	%l0 = %psr
 *	%l1 = return pc
 *	%l2 = return npc
 *	%l4 = %wim
 *	%l5 = bit for previous window
 *	%l6 = cpcb
 * If returning to a valid window, just set psr and return.
 */
rft_user:
!	sethi	%hi(_want_ast), %l7	! (done below)
	ld	[%l7 + %lo(_want_ast)], %l7
	tst	%l7			! want AST trap?
	bne,a	softtrap		! yes, re-enter trap with type T_AST
	 mov	T_AST, %o0

	btst	%l5, %l4		! if (wim & l5)
	bnz	1f			!	goto reload;
	 wr	%l0, 0, %psr		! restore cond codes
	nop				! (three instruction delay)
	RETT

	/*
	 * Previous window is invalid.
	 * Before we try to load it, we must verify its stack pointer.
	 * This is much like the underflow handler, but a bit easier
	 * since we can use our own local registers.
	 */
1:
	btst	7, %fp			! if unaligned, address is invalid
	bne	rft_invalid
	 EMPTY

	PTE_OF_ADDR(%fp, %l7, rft_invalid)
	CMP_PTE_USER_READ(%l7)		! try first page
	bne	rft_invalid		! no good
	 EMPTY
	SLT_IF_1PAGE_RW(%fp, %l7)
	bl,a	rft_user_ok		! only 1 page: ok
	 wr	%g0, 0, %wim
	add	%fp, 7*8, %l5
	PTE_OF_ADDR(%l5, %l7, rft_invalid)
	CMP_PTE_USER_READ(%l7)		! check 2nd page too
	be,a	rft_user_ok
	 wr	%g0, 0, %wim

	/*
	 * The window we wanted to pull could not be pulled.  Instead,
	 * re-enter trap with type T_RWRET.  This will pull the window
	 * into cpcb->pcb_rw[0] and set cpcb->pcb_nsaved to -1, which we
	 * will detect when we try to return again.
	 */
rft_invalid:
	b	softtrap
	 mov	T_RWRET, %o0

	/*
	 * The window we want to pull can be pulled directly.
	 */
rft_user_ok:
!	wr	%g0, 0, %wim		! allow us to get into it
	wr	%l0, 0, %psr		! fix up the cond codes now
	nop; nop; nop
	restore				! enter window I
	restore	%g0, 1, %l1		! enter window X, then %l1 = 1
	rd	%psr, %l0		! l0 = (junk << 5) + CWP;
	sll	%l1, %l0, %l1		! %wim = 1 << CWP;
	wr	%l1, 0, %wim
	sethi	%hi(_cpcb), %l1
	ld	[%l1 + %lo(_cpcb)], %l1
	and	%l0, 31, %l0
	st	%l0, [%l1 + PCB_WIM]	! cpcb->pcb_wim = l0 & 31;
	save	%g0, %g0, %g0		! back to window I
	LOADWIN(%sp)			! suck hard
	save	%g0, %g0, %g0		! back to window T
	RETT

/*
 * Return from trap.  Entered after a
 *	wr	%l0, 0, %psr
 * which disables traps so that we can rett; registers are:
 *
 *	%l0 = %psr
 *	%l1 = return pc
 *	%l2 = return npc
 *
 * (%l3..%l7 anything).
 *
 * If we are returning to user code, we must:
 *  1.  Check for register windows in the pcb that belong on the stack.
 *	If there are any, reenter trap with type T_WINOF.
 *  2.  Make sure the register windows will not underflow.  This is
 *	much easier in kernel mode....
 */
return_from_trap:
!	wr	%l0, 0, %psr		! disable traps so we can rett
! (someone else did this already)
	and	%l0, 31, %l5
	set	wmask, %l6
	ldub	[%l6 + %l5], %l5	! %l5 = 1 << ((CWP + 1) % nwindows)
	btst	PSR_PS, %l0		! returning to userland?
	bnz	rft_kernel		! no, go return to kernel
	 rd	%wim, %l4		! (read %wim in any case)

rft_user_or_recover_pcb_windows:
	/*
	 * (entered with %l4=%wim, %l5=wmask[cwp]; %l0..%l2 as usual)
	 *
	 * check cpcb->pcb_nsaved:
	 * if 0, do a `normal' return to user (see rft_user);
	 * if > 0, cpcb->pcb_rw[] holds registers to be copied to stack;
	 * if -1, cpcb->pcb_rw[0] holds user registers for rett window
	 * from an earlier T_RWRET pseudo-trap.
	 */
	sethi	%hi(_cpcb), %l6
	ld	[%l6 + %lo(_cpcb)], %l6
	ld	[%l6 + PCB_NSAVED], %l7
	tst	%l7
	bz,a	rft_user
	 sethi	%hi(_want_ast), %l7	! first instr of rft_user

	bg,a	softtrap		! if (pcb_nsaved > 0)
	 mov	T_WINOF, %o0		!	trap(T_WINOF);

	/*
	 * To get here, we must have tried to return from a previous
	 * trap and discovered that it would cause a window underflow.
	 * We then must have tried to pull the registers out of the
	 * user stack (from the address in %fp==%i6) and discovered
	 * that it was either unaligned or not loaded in memory, and
	 * therefore we ran a trap(T_RWRET), which loaded one set of
	 * registers into cpcb->pcb_pcb_rw[0] (if it had killed the
	 * process due to a bad stack, we would not be here).
	 *
	 * We want to load pcb_rw[0] into the previous window, which
	 * we know is currently invalid.  In other words, we want
	 * %wim to be 1 << ((cwp + 2) % nwindows).
	 */
	wr	%g0, 0, %wim		! enable restores
	mov	%g6, %l3		! save g6 in l3
	mov	%l6, %g6		! set g6 = &u
	st	%g0, [%g6 + PCB_NSAVED]	! clear cpcb->pcb_nsaved
	restore				! enter window I
	restore	%g0, 1, %l1		! enter window X, then %l1 = 1
	rd	%psr, %l0
	sll	%l1, %l0, %l1		! %wim = 1 << CWP;
	wr	%l1, 0, %wim
	and	%l0, 31, %l0
	st	%l0, [%g6 + PCB_WIM]	! cpcb->pcb_wim = CWP;
	nop				! unnecessary? old wim was 0...
	save	%g0, %g0, %g0		! back to window I
	LOADWIN(%g6 + PCB_RW)
	save	%g0, %g0, %g0		! back to window T (trap window)
	wr	%l0, 0, %psr		! cond codes, cond codes everywhere
	mov	%l3, %g6		! restore g6
	RETT

! exported end marker for kernel gdb
	.globl	_endtrapcode
_endtrapcode:

/*
 * init_tables(nwin) int nwin;
 *
 * Set up the uwtab and wmask tables.
 * We know nwin > 1.
 */
init_tables:
	/*
	 * for (i = -nwin, j = nwin - 2; ++i < 0; j--)
	 *	uwtab[i] = j;
	 * (loop runs at least once)
	 */
	set	uwtab, %o3
	sub	%g0, %o0, %o1		! i = -nwin + 1
	inc	%o1
	add	%o0, -2, %o2		! j = nwin - 2;
0:
	stb	%o2, [%o3 + %o1]	! uwtab[i] = j;
1:
	inccc	%o1			! ++i < 0?
	bl	0b			! yes, continue loop
	 dec	%o2			! in any case, j--

	/*
	 * (i now equals 0)
	 * for (j = nwin - 1; i < nwin; i++, j--)
	 *	uwtab[i] = j;
	 * (loop runs at least twice)
	 */
	sub	%o0, 1, %o2		! j = nwin - 1
0:
	stb	%o2, [%o3 + %o1]	! uwtab[i] = j
	inc	%o1			! i++
1:
	cmp	%o1, %o0		! i < nwin?
	bl	0b			! yes, continue
	 dec	%o2			! in any case, j--

	/*
	 * We observe that, for i in 0..nwin-2, (i+1)%nwin == i+1;
	 * for i==nwin-1, (i+1)%nwin == 0.
	 * To avoid adding 1, we run i from 1 to nwin and set
	 * wmask[i-1].
	 *
	 * for (i = j = 1; i < nwin; i++) {
	 *	j <<= 1;	(j now == 1 << i)
	 *	wmask[i - 1] = j;
	 * }
	 * (loop runs at least once)
	 */
	set	wmask - 1, %o3
	mov	1, %o1			! i = 1;
	mov	2, %o2			! j = 2;
0:
	stb	%o2, [%o3 + %o1]	! (wmask - 1)[i] = j;
	inc	%o1			! i++
	cmp	%o1, %o0		! i < nwin?
	bl,a	0b			! yes, continue
	 sll	%o2, 1, %o2		! (and j <<= 1)

	/*
	 * Now i==nwin, so we want wmask[i-1] = 1.
	 */
	mov	1, %o2			! j = 1;
	retl
	 stb	%o2, [%o3 + %o1]	! (wmask - 1)[i] = j;

dostart:
	rd	%psr, %l0		! paranoia: make sure ...
	andn	%l0, PSR_ET, %l0	! we have traps off
	wr	%l0, 0, %psr		! so that we can fiddle safely
	nop; nop; nop

	/*
	 * Startup.
	 *
	 * W