1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * wof.S: Sparc window overflow handler.
4 *
5 * Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
6 */
7
8#include <asm/contregs.h>
9#include <asm/page.h>
10#include <asm/ptrace.h>
11#include <asm/psr.h>
12#include <asm/smp.h>
13#include <asm/asi.h>
14#include <asm/winmacro.h>
15#include <asm/asmmacro.h>
16#include <asm/thread_info.h>
17
18/* WARNING: This routine is hairy and _very_ complicated, but it
19 * must be as fast as possible as it handles the allocation
20 * of register windows to the user and kernel. If you touch
21 * this code be _very_ careful as many other pieces of the
22 * kernel depend upon how this code behaves. You have been
23 * duly warned...
24 */
25
26/* We define macro's for registers which have a fixed
27 * meaning throughout this entire routine. The 'T' in
28 * the comments mean that the register can only be
29 * accessed when in the 'trap' window, 'G' means
30 * accessible in any window. Do not change these registers
31 * after they have been set, until you are ready to return
32 * from the trap.
33 */
34#define t_psr l0 /* %psr at trap time T */
35#define t_pc l1 /* PC for trap return T */
36#define t_npc l2 /* NPC for trap return T */
37#define t_wim l3 /* %wim at trap time T */
38#define saved_g5 l5 /* Global save register T */
39#define saved_g6 l6 /* Global save register T */
40#define curptr g6 /* Gets set to 'current' then stays G */
41
42/* Now registers whose values can change within the handler. */
43#define twin_tmp l4 /* Temp reg, only usable in trap window T */
44#define glob_tmp g5 /* Global temporary reg, usable anywhere G */
45
46 .text
47 .align 4
48 /* BEGINNING OF PATCH INSTRUCTIONS */
49 /* On a 7-window Sparc the boot code patches spnwin_*
50 * instructions with the following ones.
51 */
52 .globl spnwin_patch1_7win, spnwin_patch2_7win, spnwin_patch3_7win
53spnwin_patch1_7win: sll %t_wim, 6, %glob_tmp
54spnwin_patch2_7win: and %glob_tmp, 0x7f, %glob_tmp
55spnwin_patch3_7win: and %twin_tmp, 0x7f, %twin_tmp
56 /* END OF PATCH INSTRUCTIONS */
57
58 /* The trap entry point has done the following:
59 *
60 * rd %psr, %l0
61 * rd %wim, %l3
62 * b spill_window_entry
63 * andcc %l0, PSR_PS, %g0
64 */
65
66 /* Datum current_thread_info->uwinmask contains at all times a bitmask
67 * where if any user windows are active, at least one bit will
68 * be set in to mask. If no user windows are active, the bitmask
69 * will be all zeroes.
70 */
71 .globl spill_window_entry
72 .globl spnwin_patch1, spnwin_patch2, spnwin_patch3
73spill_window_entry:
74 /* LOCATION: Trap Window */
75
76 mov %g5, %saved_g5 ! save away global temp register
77 mov %g6, %saved_g6 ! save away 'current' ptr register
78
79 /* Compute what the new %wim will be if we save the
80 * window properly in this trap handler.
81 *
82 * newwim = ((%wim>>1) | (%wim<<(nwindows - 1)));
83 */
84 srl %t_wim, 0x1, %twin_tmp
85spnwin_patch1: sll %t_wim, 7, %glob_tmp
86 or %glob_tmp, %twin_tmp, %glob_tmp
87spnwin_patch2: and %glob_tmp, 0xff, %glob_tmp
88
89 /* The trap entry point has set the condition codes
90 * up for us to see if this is from user or kernel.
91 * Get the load of 'curptr' out of the way.
92 */
93 LOAD_CURRENT(curptr, twin_tmp)
94
95 andcc %t_psr, PSR_PS, %g0
96 be,a spwin_fromuser ! all user wins, branch
97 save %g0, %g0, %g0 ! Go where saving will occur
98
99 /* See if any user windows are active in the set. */
100 ld [%curptr + TI_UWINMASK], %twin_tmp ! grab win mask
101 orcc %g0, %twin_tmp, %g0 ! check for set bits
102 bne spwin_exist_uwins ! yep, there are some
103 andn %twin_tmp, %glob_tmp, %twin_tmp ! compute new uwinmask
104
105 /* Save into the window which must be saved and do it.
106 * Basically if we are here, this means that we trapped
107 * from kernel mode with only kernel windows in the register
108 * file.
109 */
110 save %g0, %g0, %g0 ! save into the window to stash away
111 wr %glob_tmp, 0x0, %wim ! set new %wim, this is safe now
112
113spwin_no_userwins_from_kernel:
114 /* LOCATION: Window to be saved */
115
116 STORE_WINDOW(sp) ! stash the window
117 restore %g0, %g0, %g0 ! go back into trap window
118
119 /* LOCATION: Trap window */
120 mov %saved_g5, %g5 ! restore %glob_tmp
121 mov %saved_g6, %g6 ! restore %curptr
122 wr %t_psr, 0x0, %psr ! restore condition codes in %psr
123 WRITE_PAUSE ! waste some time
124 jmp %t_pc ! Return from trap
125 rett %t_npc ! we are done
126
127spwin_exist_uwins:
128 /* LOCATION: Trap window */
129
130 /* Wow, user windows have to be dealt with, this is dirty
131 * and messy as all hell. And difficult to follow if you
132 * are approaching the infamous register window trap handling
133 * problem for the first time. DON'T LOOK!
134 *
135 * Note that how the execution path works out, the new %wim
136 * will be left for us in the global temporary register,
137 * %glob_tmp. We cannot set the new %wim first because we
138 * need to save into the appropriate window without inducing
139 * a trap (traps are off, we'd get a watchdog wheee)...
140 * But first, store the new user window mask calculated
141 * above.
142 */
143 st %twin_tmp, [%curptr + TI_UWINMASK]
144 save %g0, %g0, %g0 ! Go to where the saving will occur
145
146spwin_fromuser:
147 /* LOCATION: Window to be saved */
148 wr %glob_tmp, 0x0, %wim ! Now it is safe to set new %wim
149
150 /* LOCATION: Window to be saved */
151
152 /* This instruction branches to a routine which will check
153 * to validity of the users stack pointer by whatever means
154 * are necessary. This means that this is architecture
155 * specific and thus this branch instruction will need to
156 * be patched at boot time once the machine type is known.
157 * This routine _shall not_ touch %curptr under any
158 * circumstances whatsoever! It will branch back to the
159 * label 'spwin_good_ustack' if the stack is ok but still
160 * needs to be dumped (SRMMU for instance will not need to
161 * do this) or 'spwin_finish_up' if the stack is ok and the
162 * registers have already been saved. If the stack is found
163 * to be bogus for some reason the routine shall branch to
164 * the label 'spwin_user_stack_is_bolixed' which will take
165 * care of things at that point.
166 */
167 b spwin_srmmu_stackchk
168 andcc %sp, 0x7, %g0
169
170spwin_good_ustack:
171 /* LOCATION: Window to be saved */
172
173 /* The users stack is ok and we can safely save it at
174 * %sp.
175 */
176 STORE_WINDOW(sp)
177
178spwin_finish_up:
179 restore %g0, %g0, %g0 /* Back to trap window. */
180
181 /* LOCATION: Trap window */
182
183 /* We have spilled successfully, and we have properly stored
184 * the appropriate window onto the stack.
185 */
186
187 /* Restore saved globals */
188 mov %saved_g5, %g5
189 mov %saved_g6, %g6
190
191 wr %t_psr, 0x0, %psr
192 WRITE_PAUSE
193 jmp %t_pc
194 rett %t_npc
195
196spwin_user_stack_is_bolixed:
197 /* LOCATION: Window to be saved */
198
199 /* Wheee, user has trashed his/her stack. We have to decide
200 * how to proceed based upon whether we came from kernel mode
201 * or not. If we came from kernel mode, toss the window into
202 * a special buffer and proceed, the kernel _needs_ a window
203 * and we could be in an interrupt handler so timing is crucial.
204 * If we came from user land we build a full stack frame and call
205 * c-code to gun down the process.
206 */
207 rd %psr, %glob_tmp
208 andcc %glob_tmp, PSR_PS, %g0
209 bne spwin_bad_ustack_from_kernel
210 nop
211
212 /* Oh well, throw this one window into the per-task window
213 * buffer, the first one.
214 */
215 st %sp, [%curptr + TI_RWIN_SPTRS]
216 STORE_WINDOW(curptr + TI_REG_WINDOW)
217 restore %g0, %g0, %g0
218
219 /* LOCATION: Trap Window */
220
221 /* Back in the trap window, update winbuffer save count. */
222 mov 1, %twin_tmp
223 st %twin_tmp, [%curptr + TI_W_SAVED]
224
225 /* Compute new user window mask. What we are basically
226 * doing is taking two windows, the invalid one at trap
227 * time and the one we attempted to throw onto the users
228 * stack, and saying that everything else is an ok user
229 * window. umask = ((~(%t_wim | %wim)) & valid_wim_bits)
230 */
231 rd %wim, %twin_tmp
232 or %twin_tmp, %t_wim, %twin_tmp
233 not %twin_tmp
234spnwin_patch3: and %twin_tmp, 0xff, %twin_tmp ! patched on 7win Sparcs
235 st %twin_tmp, [%curptr + TI_UWINMASK]
236
237#define STACK_OFFSET (THREAD_SIZE - TRACEREG_SZ - STACKFRAME_SZ)
238
239 sethi %hi(STACK_OFFSET), %sp
240 or %sp, %lo(STACK_OFFSET), %sp
241 add %curptr, %sp, %sp
242
243 /* Restore the saved globals and build a pt_regs frame. */
244 mov %saved_g5, %g5
245 mov %saved_g6, %g6
246 STORE_PT_ALL(sp, t_psr, t_pc, t_npc, g1)
247
248 sethi %hi(STACK_OFFSET), %g6
249 or %g6, %lo(STACK_OFFSET), %g6
250 sub %sp, %g6, %g6 ! curptr
251
252 /* Turn on traps and call c-code to deal with it. */
253 wr %t_psr, PSR_ET, %psr
254 nop
255 call window_overflow_fault
256 nop
257
258 /* Return from trap if C-code actually fixes things, if it
259 * doesn't then we never get this far as the process will
260 * be given the look of death from Commander Peanut.
261 */
262 b ret_trap_entry
263 clr %l6
264
265spwin_bad_ustack_from_kernel:
266 /* LOCATION: Window to be saved */
267
268 /* The kernel provoked a spill window trap, but the window we
269 * need to save is a user one and the process has trashed its
270 * stack pointer. We need to be quick, so we throw it into
271 * a per-process window buffer until we can properly handle
272 * this later on.
273 */
274 SAVE_BOLIXED_USER_STACK(curptr, glob_tmp)
275 restore %g0, %g0, %g0
276
277 /* LOCATION: Trap window */
278
279 /* Restore globals, condition codes in the %psr and
280 * return from trap. Note, restoring %g6 when returning
281 * to kernel mode is not necessarily these days. ;-)
282 */
283 mov %saved_g5, %g5
284 mov %saved_g6, %g6
285
286 wr %t_psr, 0x0, %psr
287 WRITE_PAUSE
288
289 jmp %t_pc
290 rett %t_npc
291
292/* Undefine the register macros which would only cause trouble
293 * if used below. This helps find 'stupid' coding errors that
294 * produce 'odd' behavior. The routines below are allowed to
295 * make usage of glob_tmp and t_psr so we leave them defined.
296 */
297#undef twin_tmp
298#undef curptr
299#undef t_pc
300#undef t_npc
301#undef t_wim
302#undef saved_g5
303#undef saved_g6
304
305/* Now come the per-architecture window overflow stack checking routines.
306 * As noted above %curptr cannot be touched by this routine at all.
307 */
308
309 /* This is a generic SRMMU routine. As far as I know this
310 * works for all current v8/srmmu implementations, we'll
311 * see...
312 */
313 .globl spwin_srmmu_stackchk
314spwin_srmmu_stackchk:
315 /* LOCATION: Window to be saved on the stack */
316
317 /* Because of SMP concerns and speed we play a trick.
318 * We disable fault traps in the MMU control register,
319 * Execute the stores, then check the fault registers
320 * to see what happens. I can hear Linus now
321 * "disgusting... broken hardware...".
322 *
323 * But first, check to see if the users stack has ended
324 * up in kernel vma, then we would succeed for the 'wrong'
325 * reason... ;( Note that the 'sethi' below assumes the
326 * kernel is page aligned, which should always be the case.
327 */
328 /* Check results of callers andcc %sp, 0x7, %g0 */
329 bne spwin_user_stack_is_bolixed
330 sethi %hi(PAGE_OFFSET), %glob_tmp
331 cmp %glob_tmp, %sp
332 bleu spwin_user_stack_is_bolixed
333 mov AC_M_SFSR, %glob_tmp
334
335 /* Clear the fault status and turn on the no_fault bit. */
336LEON_PI(lda [%glob_tmp] ASI_LEON_MMUREGS, %g0) ! eat SFSR
337SUN_PI_(lda [%glob_tmp] ASI_M_MMUREGS, %g0) ! eat SFSR
338
339LEON_PI(lda [%g0] ASI_LEON_MMUREGS, %glob_tmp) ! read MMU control
340SUN_PI_(lda [%g0] ASI_M_MMUREGS, %glob_tmp) ! read MMU control
341 or %glob_tmp, 0x2, %glob_tmp ! or in no_fault bit
342LEON_PI(sta %glob_tmp, [%g0] ASI_LEON_MMUREGS) ! set it
343SUN_PI_(sta %glob_tmp, [%g0] ASI_M_MMUREGS) ! set it
344
345 /* Dump the registers and cross fingers. */
346 STORE_WINDOW(sp)
347
348 /* Clear the no_fault bit and check the status. */
349 andn %glob_tmp, 0x2, %glob_tmp
350LEON_PI(sta %glob_tmp, [%g0] ASI_LEON_MMUREGS)
351SUN_PI_(sta %glob_tmp, [%g0] ASI_M_MMUREGS)
352
353 mov AC_M_SFAR, %glob_tmp
354LEON_PI(lda [%glob_tmp] ASI_LEON_MMUREGS, %g0)
355SUN_PI_(lda [%glob_tmp] ASI_M_MMUREGS, %g0)
356
357 mov AC_M_SFSR, %glob_tmp
358LEON_PI(lda [%glob_tmp] ASI_LEON_MMUREGS, %glob_tmp)
359SUN_PI_(lda [%glob_tmp] ASI_M_MMUREGS, %glob_tmp)
360 andcc %glob_tmp, 0x2, %g0 ! did we fault?
361 be,a spwin_finish_up + 0x4 ! cool beans, success
362 restore %g0, %g0, %g0
363
364 rd %psr, %glob_tmp
365 b spwin_user_stack_is_bolixed + 0x4 ! we faulted, ugh
366 nop
367

source code of linux/arch/sparc/kernel/wof.S