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+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * wof.S: Sparc window overflow handler.
+ *
+ * Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
+ */
+
+#include <asm/contregs.h>
+#include <asm/page.h>
+#include <asm/ptrace.h>
+#include <asm/psr.h>
+#include <asm/smp.h>
+#include <asm/asi.h>
+#include <asm/winmacro.h>
+#include <asm/asmmacro.h>
+#include <asm/thread_info.h>
+
+/* WARNING: This routine is hairy and _very_ complicated, but it
+ * must be as fast as possible as it handles the allocation
+ * of register windows to the user and kernel. If you touch
+ * this code be _very_ careful as many other pieces of the
+ * kernel depend upon how this code behaves. You have been
+ * duly warned...
+ */
+
+/* We define macro's for registers which have a fixed
+ * meaning throughout this entire routine. The 'T' in
+ * the comments mean that the register can only be
+ * accessed when in the 'trap' window, 'G' means
+ * accessible in any window. Do not change these registers
+ * after they have been set, until you are ready to return
+ * from the trap.
+ */
+#define t_psr l0 /* %psr at trap time T */
+#define t_pc l1 /* PC for trap return T */
+#define t_npc l2 /* NPC for trap return T */
+#define t_wim l3 /* %wim at trap time T */
+#define saved_g5 l5 /* Global save register T */
+#define saved_g6 l6 /* Global save register T */
+#define curptr g6 /* Gets set to 'current' then stays G */
+
+/* Now registers whose values can change within the handler. */
+#define twin_tmp l4 /* Temp reg, only usable in trap window T */
+#define glob_tmp g5 /* Global temporary reg, usable anywhere G */
+
+ .text
+ .align 4
+ /* BEGINNING OF PATCH INSTRUCTIONS */
+ /* On a 7-window Sparc the boot code patches spnwin_*
+ * instructions with the following ones.
+ */
+ .globl spnwin_patch1_7win, spnwin_patch2_7win, spnwin_patch3_7win
+spnwin_patch1_7win: sll %t_wim, 6, %glob_tmp
+spnwin_patch2_7win: and %glob_tmp, 0x7f, %glob_tmp
+spnwin_patch3_7win: and %twin_tmp, 0x7f, %twin_tmp
+ /* END OF PATCH INSTRUCTIONS */
+
+ /* The trap entry point has done the following:
+ *
+ * rd %psr, %l0
+ * rd %wim, %l3
+ * b spill_window_entry
+ * andcc %l0, PSR_PS, %g0
+ */
+
+ /* Datum current_thread_info->uwinmask contains at all times a bitmask
+ * where if any user windows are active, at least one bit will
+ * be set in to mask. If no user windows are active, the bitmask
+ * will be all zeroes.
+ */
+ .globl spill_window_entry
+ .globl spnwin_patch1, spnwin_patch2, spnwin_patch3
+spill_window_entry:
+ /* LOCATION: Trap Window */
+
+ mov %g5, %saved_g5 ! save away global temp register
+ mov %g6, %saved_g6 ! save away 'current' ptr register
+
+ /* Compute what the new %wim will be if we save the
+ * window properly in this trap handler.
+ *
+ * newwim = ((%wim>>1) | (%wim<<(nwindows - 1)));
+ */
+ srl %t_wim, 0x1, %twin_tmp
+spnwin_patch1: sll %t_wim, 7, %glob_tmp
+ or %glob_tmp, %twin_tmp, %glob_tmp
+spnwin_patch2: and %glob_tmp, 0xff, %glob_tmp
+
+ /* The trap entry point has set the condition codes
+ * up for us to see if this is from user or kernel.
+ * Get the load of 'curptr' out of the way.
+ */
+ LOAD_CURRENT(curptr, twin_tmp)
+
+ andcc %t_psr, PSR_PS, %g0
+ be,a spwin_fromuser ! all user wins, branch
+ save %g0, %g0, %g0 ! Go where saving will occur
+
+ /* See if any user windows are active in the set. */
+ ld [%curptr + TI_UWINMASK], %twin_tmp ! grab win mask
+ orcc %g0, %twin_tmp, %g0 ! check for set bits
+ bne spwin_exist_uwins ! yep, there are some
+ andn %twin_tmp, %glob_tmp, %twin_tmp ! compute new uwinmask
+
+ /* Save into the window which must be saved and do it.
+ * Basically if we are here, this means that we trapped
+ * from kernel mode with only kernel windows in the register
+ * file.
+ */
+ save %g0, %g0, %g0 ! save into the window to stash away
+ wr %glob_tmp, 0x0, %wim ! set new %wim, this is safe now
+
+spwin_no_userwins_from_kernel:
+ /* LOCATION: Window to be saved */
+
+ STORE_WINDOW(sp) ! stash the window
+ restore %g0, %g0, %g0 ! go back into trap window
+
+ /* LOCATION: Trap window */
+ mov %saved_g5, %g5 ! restore %glob_tmp
+ mov %saved_g6, %g6 ! restore %curptr
+ wr %t_psr, 0x0, %psr ! restore condition codes in %psr
+ WRITE_PAUSE ! waste some time
+ jmp %t_pc ! Return from trap
+ rett %t_npc ! we are done
+
+spwin_exist_uwins:
+ /* LOCATION: Trap window */
+
+ /* Wow, user windows have to be dealt with, this is dirty
+ * and messy as all hell. And difficult to follow if you
+ * are approaching the infamous register window trap handling
+ * problem for the first time. DON'T LOOK!
+ *
+ * Note that how the execution path works out, the new %wim
+ * will be left for us in the global temporary register,
+ * %glob_tmp. We cannot set the new %wim first because we
+ * need to save into the appropriate window without inducing
+ * a trap (traps are off, we'd get a watchdog wheee)...
+ * But first, store the new user window mask calculated
+ * above.
+ */
+ st %twin_tmp, [%curptr + TI_UWINMASK]
+ save %g0, %g0, %g0 ! Go to where the saving will occur
+
+spwin_fromuser:
+ /* LOCATION: Window to be saved */
+ wr %glob_tmp, 0x0, %wim ! Now it is safe to set new %wim
+
+ /* LOCATION: Window to be saved */
+
+ /* This instruction branches to a routine which will check
+ * to validity of the users stack pointer by whatever means
+ * are necessary. This means that this is architecture
+ * specific and thus this branch instruction will need to
+ * be patched at boot time once the machine type is known.
+ * This routine _shall not_ touch %curptr under any
+ * circumstances whatsoever! It will branch back to the
+ * label 'spwin_good_ustack' if the stack is ok but still
+ * needs to be dumped (SRMMU for instance will not need to
+ * do this) or 'spwin_finish_up' if the stack is ok and the
+ * registers have already been saved. If the stack is found
+ * to be bogus for some reason the routine shall branch to
+ * the label 'spwin_user_stack_is_bolixed' which will take
+ * care of things at that point.
+ */
+ b spwin_srmmu_stackchk
+ andcc %sp, 0x7, %g0
+
+spwin_good_ustack:
+ /* LOCATION: Window to be saved */
+
+ /* The users stack is ok and we can safely save it at
+ * %sp.
+ */
+ STORE_WINDOW(sp)
+
+spwin_finish_up:
+ restore %g0, %g0, %g0 /* Back to trap window. */
+
+ /* LOCATION: Trap window */
+
+ /* We have spilled successfully, and we have properly stored
+ * the appropriate window onto the stack.
+ */
+
+ /* Restore saved globals */
+ mov %saved_g5, %g5
+ mov %saved_g6, %g6
+
+ wr %t_psr, 0x0, %psr
+ WRITE_PAUSE
+ jmp %t_pc
+ rett %t_npc
+
+spwin_user_stack_is_bolixed:
+ /* LOCATION: Window to be saved */
+
+ /* Wheee, user has trashed his/her stack. We have to decide
+ * how to proceed based upon whether we came from kernel mode
+ * or not. If we came from kernel mode, toss the window into
+ * a special buffer and proceed, the kernel _needs_ a window
+ * and we could be in an interrupt handler so timing is crucial.
+ * If we came from user land we build a full stack frame and call
+ * c-code to gun down the process.
+ */
+ rd %psr, %glob_tmp
+ andcc %glob_tmp, PSR_PS, %g0
+ bne spwin_bad_ustack_from_kernel
+ nop
+
+ /* Oh well, throw this one window into the per-task window
+ * buffer, the first one.
+ */
+ st %sp, [%curptr + TI_RWIN_SPTRS]
+ STORE_WINDOW(curptr + TI_REG_WINDOW)
+ restore %g0, %g0, %g0
+
+ /* LOCATION: Trap Window */
+
+ /* Back in the trap window, update winbuffer save count. */
+ mov 1, %twin_tmp
+ st %twin_tmp, [%curptr + TI_W_SAVED]
+
+ /* Compute new user window mask. What we are basically
+ * doing is taking two windows, the invalid one at trap
+ * time and the one we attempted to throw onto the users
+ * stack, and saying that everything else is an ok user
+ * window. umask = ((~(%t_wim | %wim)) & valid_wim_bits)
+ */
+ rd %wim, %twin_tmp
+ or %twin_tmp, %t_wim, %twin_tmp
+ not %twin_tmp
+spnwin_patch3: and %twin_tmp, 0xff, %twin_tmp ! patched on 7win Sparcs
+ st %twin_tmp, [%curptr + TI_UWINMASK]
+
+#define STACK_OFFSET (THREAD_SIZE - TRACEREG_SZ - STACKFRAME_SZ)
+
+ sethi %hi(STACK_OFFSET), %sp
+ or %sp, %lo(STACK_OFFSET), %sp
+ add %curptr, %sp, %sp
+
+ /* Restore the saved globals and build a pt_regs frame. */
+ mov %saved_g5, %g5
+ mov %saved_g6, %g6
+ STORE_PT_ALL(sp, t_psr, t_pc, t_npc, g1)
+
+ sethi %hi(STACK_OFFSET), %g6
+ or %g6, %lo(STACK_OFFSET), %g6
+ sub %sp, %g6, %g6 ! curptr
+
+ /* Turn on traps and call c-code to deal with it. */
+ wr %t_psr, PSR_ET, %psr
+ nop
+ call window_overflow_fault
+ nop
+
+ /* Return from trap if C-code actually fixes things, if it
+ * doesn't then we never get this far as the process will
+ * be given the look of death from Commander Peanut.
+ */
+ b ret_trap_entry
+ clr %l6
+
+spwin_bad_ustack_from_kernel:
+ /* LOCATION: Window to be saved */
+
+ /* The kernel provoked a spill window trap, but the window we
+ * need to save is a user one and the process has trashed its
+ * stack pointer. We need to be quick, so we throw it into
+ * a per-process window buffer until we can properly handle
+ * this later on.
+ */
+ SAVE_BOLIXED_USER_STACK(curptr, glob_tmp)
+ restore %g0, %g0, %g0
+
+ /* LOCATION: Trap window */
+
+ /* Restore globals, condition codes in the %psr and
+ * return from trap. Note, restoring %g6 when returning
+ * to kernel mode is not necessarily these days. ;-)
+ */
+ mov %saved_g5, %g5
+ mov %saved_g6, %g6
+
+ wr %t_psr, 0x0, %psr
+ WRITE_PAUSE
+
+ jmp %t_pc
+ rett %t_npc
+
+/* Undefine the register macros which would only cause trouble
+ * if used below. This helps find 'stupid' coding errors that
+ * produce 'odd' behavior. The routines below are allowed to
+ * make usage of glob_tmp and t_psr so we leave them defined.
+ */
+#undef twin_tmp
+#undef curptr
+#undef t_pc
+#undef t_npc
+#undef t_wim
+#undef saved_g5
+#undef saved_g6
+
+/* Now come the per-architecture window overflow stack checking routines.
+ * As noted above %curptr cannot be touched by this routine at all.
+ */
+
+ /* This is a generic SRMMU routine. As far as I know this
+ * works for all current v8/srmmu implementations, we'll
+ * see...
+ */
+ .globl spwin_srmmu_stackchk
+spwin_srmmu_stackchk:
+ /* LOCATION: Window to be saved on the stack */
+
+ /* Because of SMP concerns and speed we play a trick.
+ * We disable fault traps in the MMU control register,
+ * Execute the stores, then check the fault registers
+ * to see what happens. I can hear Linus now
+ * "disgusting... broken hardware...".
+ *
+ * But first, check to see if the users stack has ended
+ * up in kernel vma, then we would succeed for the 'wrong'
+ * reason... ;( Note that the 'sethi' below assumes the
+ * kernel is page aligned, which should always be the case.
+ */
+ /* Check results of callers andcc %sp, 0x7, %g0 */
+ bne spwin_user_stack_is_bolixed
+ sethi %hi(PAGE_OFFSET), %glob_tmp
+ cmp %glob_tmp, %sp
+ bleu spwin_user_stack_is_bolixed
+ mov AC_M_SFSR, %glob_tmp
+
+ /* Clear the fault status and turn on the no_fault bit. */
+LEON_PI(lda [%glob_tmp] ASI_LEON_MMUREGS, %g0) ! eat SFSR
+SUN_PI_(lda [%glob_tmp] ASI_M_MMUREGS, %g0) ! eat SFSR
+
+LEON_PI(lda [%g0] ASI_LEON_MMUREGS, %glob_tmp) ! read MMU control
+SUN_PI_(lda [%g0] ASI_M_MMUREGS, %glob_tmp) ! read MMU control
+ or %glob_tmp, 0x2, %glob_tmp ! or in no_fault bit
+LEON_PI(sta %glob_tmp, [%g0] ASI_LEON_MMUREGS) ! set it
+SUN_PI_(sta %glob_tmp, [%g0] ASI_M_MMUREGS) ! set it
+
+ /* Dump the registers and cross fingers. */
+ STORE_WINDOW(sp)
+
+ /* Clear the no_fault bit and check the status. */
+ andn %glob_tmp, 0x2, %glob_tmp
+LEON_PI(sta %glob_tmp, [%g0] ASI_LEON_MMUREGS)
+SUN_PI_(sta %glob_tmp, [%g0] ASI_M_MMUREGS)
+
+ mov AC_M_SFAR, %glob_tmp
+LEON_PI(lda [%glob_tmp] ASI_LEON_MMUREGS, %g0)
+SUN_PI_(lda [%glob_tmp] ASI_M_MMUREGS, %g0)
+
+ mov AC_M_SFSR, %glob_tmp
+LEON_PI(lda [%glob_tmp] ASI_LEON_MMUREGS, %glob_tmp)
+SUN_PI_(lda [%glob_tmp] ASI_M_MMUREGS, %glob_tmp)
+ andcc %glob_tmp, 0x2, %g0 ! did we fault?
+ be,a spwin_finish_up + 0x4 ! cool beans, success
+ restore %g0, %g0, %g0
+
+ rd %psr, %glob_tmp
+ b spwin_user_stack_is_bolixed + 0x4 ! we faulted, ugh
+ nop