xref: /openbmc/linux/arch/arm/kernel/entry-header.S (revision 24a9c541)
1/* SPDX-License-Identifier: GPL-2.0 */
2#include <linux/init.h>
3#include <linux/linkage.h>
4
5#include <asm/assembler.h>
6#include <asm/asm-offsets.h>
7#include <asm/errno.h>
8#include <asm/thread_info.h>
9#include <asm/uaccess-asm.h>
10#include <asm/v7m.h>
11
12@ Bad Abort numbers
13@ -----------------
14@
15#define BAD_PREFETCH	0
16#define BAD_DATA	1
17#define BAD_ADDREXCPTN	2
18#define BAD_IRQ		3
19#define BAD_UNDEFINSTR	4
20
21@
22@ Most of the stack format comes from struct pt_regs, but with
23@ the addition of 8 bytes for storing syscall args 5 and 6.
24@ This _must_ remain a multiple of 8 for EABI.
25@
26#define S_OFF		8
27
28/*
29 * The SWI code relies on the fact that R0 is at the bottom of the stack
30 * (due to slow/fast restore user regs).
31 */
32#if S_R0 != 0
33#error "Please fix"
34#endif
35
36	.macro	zero_fp
37#ifdef CONFIG_FRAME_POINTER
38	mov	fp, #0
39#endif
40	.endm
41
42#ifdef CONFIG_ALIGNMENT_TRAP
43#define ATRAP(x...) x
44#else
45#define ATRAP(x...)
46#endif
47
48	.macro	alignment_trap, rtmp1, rtmp2, label
49#ifdef CONFIG_ALIGNMENT_TRAP
50	mrc	p15, 0, \rtmp2, c1, c0, 0
51	ldr_va	\rtmp1, \label
52	teq	\rtmp1, \rtmp2
53	mcrne	p15, 0, \rtmp1, c1, c0, 0
54#endif
55	.endm
56
57#ifdef CONFIG_CPU_V7M
58/*
59 * ARMv7-M exception entry/exit macros.
60 *
61 * xPSR, ReturnAddress(), LR (R14), R12, R3, R2, R1, and R0 are
62 * automatically saved on the current stack (32 words) before
63 * switching to the exception stack (SP_main).
64 *
65 * If exception is taken while in user mode, SP_main is
66 * empty. Otherwise, SP_main is aligned to 64 bit automatically
67 * (CCR.STKALIGN set).
68 *
69 * Linux assumes that the interrupts are disabled when entering an
70 * exception handler and it may BUG if this is not the case. Interrupts
71 * are disabled during entry and reenabled in the exit macro.
72 *
73 * v7m_exception_slow_exit is used when returning from SVC or PendSV.
74 * When returning to kernel mode, we don't return from exception.
75 */
76	.macro	v7m_exception_entry
77	@ determine the location of the registers saved by the core during
78	@ exception entry. Depending on the mode the cpu was in when the
79	@ exception happend that is either on the main or the process stack.
80	@ Bit 2 of EXC_RETURN stored in the lr register specifies which stack
81	@ was used.
82	tst	lr, #EXC_RET_STACK_MASK
83	mrsne	r12, psp
84	moveq	r12, sp
85
86	@ we cannot rely on r0-r3 and r12 matching the value saved in the
87	@ exception frame because of tail-chaining. So these have to be
88	@ reloaded.
89	ldmia	r12!, {r0-r3}
90
91	@ Linux expects to have irqs off. Do it here before taking stack space
92	cpsid	i
93
94	sub	sp, #PT_REGS_SIZE-S_IP
95	stmdb	sp!, {r0-r11}
96
97	@ load saved r12, lr, return address and xPSR.
98	@ r0-r7 are used for signals and never touched from now on. Clobbering
99	@ r8-r12 is OK.
100	mov	r9, r12
101	ldmia	r9!, {r8, r10-r12}
102
103	@ calculate the original stack pointer value.
104	@ r9 currently points to the memory location just above the auto saved
105	@ xPSR.
106	@ The cpu might automatically 8-byte align the stack. Bit 9
107	@ of the saved xPSR specifies if stack aligning took place. In this case
108	@ another 32-bit value is included in the stack.
109
110	tst	r12, V7M_xPSR_FRAMEPTRALIGN
111	addne	r9, r9, #4
112
113	@ store saved r12 using str to have a register to hold the base for stm
114	str	r8, [sp, #S_IP]
115	add	r8, sp, #S_SP
116	@ store r13-r15, xPSR
117	stmia	r8!, {r9-r12}
118	@ store old_r0
119	str	r0, [r8]
120	.endm
121
122        /*
123	 * PENDSV and SVCALL are configured to have the same exception
124	 * priorities. As a kernel thread runs at SVCALL execution priority it
125	 * can never be preempted and so we will never have to return to a
126	 * kernel thread here.
127         */
128	.macro	v7m_exception_slow_exit ret_r0
129	cpsid	i
130	ldr	lr, =exc_ret
131	ldr	lr, [lr]
132
133	@ read original r12, sp, lr, pc and xPSR
134	add	r12, sp, #S_IP
135	ldmia	r12, {r1-r5}
136
137	@ an exception frame is always 8-byte aligned. To tell the hardware if
138	@ the sp to be restored is aligned or not set bit 9 of the saved xPSR
139	@ accordingly.
140	tst	r2, #4
141	subne	r2, r2, #4
142	orrne	r5, V7M_xPSR_FRAMEPTRALIGN
143	biceq	r5, V7M_xPSR_FRAMEPTRALIGN
144
145	@ ensure bit 0 is cleared in the PC, otherwise behaviour is
146	@ unpredictable
147	bic	r4, #1
148
149	@ write basic exception frame
150	stmdb	r2!, {r1, r3-r5}
151	ldmia	sp, {r1, r3-r5}
152	.if	\ret_r0
153	stmdb	r2!, {r0, r3-r5}
154	.else
155	stmdb	r2!, {r1, r3-r5}
156	.endif
157
158	@ restore process sp
159	msr	psp, r2
160
161	@ restore original r4-r11
162	ldmia	sp!, {r0-r11}
163
164	@ restore main sp
165	add	sp, sp, #PT_REGS_SIZE-S_IP
166
167	cpsie	i
168	bx	lr
169	.endm
170#endif	/* CONFIG_CPU_V7M */
171
172	@
173	@ Store/load the USER SP and LR registers by switching to the SYS
174	@ mode. Useful in Thumb-2 mode where "stm/ldm rd, {sp, lr}^" is not
175	@ available. Should only be called from SVC mode
176	@
177	.macro	store_user_sp_lr, rd, rtemp, offset = 0
178	mrs	\rtemp, cpsr
179	eor	\rtemp, \rtemp, #(SVC_MODE ^ SYSTEM_MODE)
180	msr	cpsr_c, \rtemp			@ switch to the SYS mode
181
182	str	sp, [\rd, #\offset]		@ save sp_usr
183	str	lr, [\rd, #\offset + 4]		@ save lr_usr
184
185	eor	\rtemp, \rtemp, #(SVC_MODE ^ SYSTEM_MODE)
186	msr	cpsr_c, \rtemp			@ switch back to the SVC mode
187	.endm
188
189	.macro	load_user_sp_lr, rd, rtemp, offset = 0
190	mrs	\rtemp, cpsr
191	eor	\rtemp, \rtemp, #(SVC_MODE ^ SYSTEM_MODE)
192	msr	cpsr_c, \rtemp			@ switch to the SYS mode
193
194	ldr	sp, [\rd, #\offset]		@ load sp_usr
195	ldr	lr, [\rd, #\offset + 4]		@ load lr_usr
196
197	eor	\rtemp, \rtemp, #(SVC_MODE ^ SYSTEM_MODE)
198	msr	cpsr_c, \rtemp			@ switch back to the SVC mode
199	.endm
200
201
202	.macro	svc_exit, rpsr, irq = 0
203	.if	\irq != 0
204	@ IRQs already off
205#ifdef CONFIG_TRACE_IRQFLAGS
206	@ The parent context IRQs must have been enabled to get here in
207	@ the first place, so there's no point checking the PSR I bit.
208	bl	trace_hardirqs_on
209#endif
210	.else
211	@ IRQs off again before pulling preserved data off the stack
212	disable_irq_notrace
213#ifdef CONFIG_TRACE_IRQFLAGS
214	tst	\rpsr, #PSR_I_BIT
215	bleq	trace_hardirqs_on
216	tst	\rpsr, #PSR_I_BIT
217	blne	trace_hardirqs_off
218#endif
219	.endif
220	uaccess_exit tsk, r0, r1
221
222#ifndef CONFIG_THUMB2_KERNEL
223	@ ARM mode SVC restore
224	msr	spsr_cxsf, \rpsr
225#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_32v6K)
226	@ We must avoid clrex due to Cortex-A15 erratum #830321
227	sub	r0, sp, #4			@ uninhabited address
228	strex	r1, r2, [r0]			@ clear the exclusive monitor
229#endif
230	ldmia	sp, {r0 - pc}^			@ load r0 - pc, cpsr
231#else
232	@ Thumb mode SVC restore
233	ldr	lr, [sp, #S_SP]			@ top of the stack
234	ldrd	r0, r1, [sp, #S_LR]		@ calling lr and pc
235
236	@ We must avoid clrex due to Cortex-A15 erratum #830321
237	strex	r2, r1, [sp, #S_LR]		@ clear the exclusive monitor
238
239	stmdb	lr!, {r0, r1, \rpsr}		@ calling lr and rfe context
240	ldmia	sp, {r0 - r12}
241	mov	sp, lr
242	ldr	lr, [sp], #4
243	rfeia	sp!
244#endif
245	.endm
246
247	@
248	@ svc_exit_via_fiq - like svc_exit but switches to FIQ mode before exit
249	@
250	@ This macro acts in a similar manner to svc_exit but switches to FIQ
251	@ mode to restore the final part of the register state.
252	@
253	@ We cannot use the normal svc_exit procedure because that would
254	@ clobber spsr_svc (FIQ could be delivered during the first few
255	@ instructions of vector_swi meaning its contents have not been
256	@ saved anywhere).
257	@
258	@ Note that, unlike svc_exit, this macro also does not allow a caller
259	@ supplied rpsr. This is because the FIQ exceptions are not re-entrant
260	@ and the handlers cannot call into the scheduler (meaning the value
261	@ on the stack remains correct).
262	@
263	.macro  svc_exit_via_fiq
264	uaccess_exit tsk, r0, r1
265#ifndef CONFIG_THUMB2_KERNEL
266	@ ARM mode restore
267	mov	r0, sp
268	ldmib	r0, {r1 - r14}	@ abort is deadly from here onward (it will
269				@ clobber state restored below)
270	msr	cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
271	add	r8, r0, #S_PC
272	ldr	r9, [r0, #S_PSR]
273	msr	spsr_cxsf, r9
274	ldr	r0, [r0, #S_R0]
275	ldmia	r8, {pc}^
276#else
277	@ Thumb mode restore
278	add	r0, sp, #S_R2
279	ldr	lr, [sp, #S_LR]
280	ldr	sp, [sp, #S_SP] @ abort is deadly from here onward (it will
281			        @ clobber state restored below)
282	ldmia	r0, {r2 - r12}
283	mov	r1, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
284	msr	cpsr_c, r1
285	sub	r0, #S_R2
286	add	r8, r0, #S_PC
287	ldmia	r0, {r0 - r1}
288	rfeia	r8
289#endif
290	.endm
291
292
293	.macro	restore_user_regs, fast = 0, offset = 0
294#if defined(CONFIG_CPU_32v6K) && \
295    (!defined(CONFIG_CPU_V6) || defined(CONFIG_SMP))
296#ifdef CONFIG_CPU_V6
297ALT_SMP(nop)
298ALT_UP_B(.L1_\@)
299#endif
300	@ The TLS register update is deferred until return to user space so we
301	@ can use it for other things while running in the kernel
302	mrc	p15, 0, r1, c13, c0, 3		@ get current_thread_info pointer
303	ldr	r1, [r1, #TI_TP_VALUE]
304	mcr	p15, 0, r1, c13, c0, 3		@ set TLS register
305.L1_\@:
306#endif
307
308	uaccess_enable r1, isb=0
309#ifndef CONFIG_THUMB2_KERNEL
310	@ ARM mode restore
311	mov	r2, sp
312	ldr	r1, [r2, #\offset + S_PSR]	@ get calling cpsr
313	ldr	lr, [r2, #\offset + S_PC]!	@ get pc
314	tst	r1, #PSR_I_BIT | 0x0f
315	bne	1f
316	msr	spsr_cxsf, r1			@ save in spsr_svc
317#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_32v6K)
318	@ We must avoid clrex due to Cortex-A15 erratum #830321
319	strex	r1, r2, [r2]			@ clear the exclusive monitor
320#endif
321	.if	\fast
322	ldmdb	r2, {r1 - lr}^			@ get calling r1 - lr
323	.else
324	ldmdb	r2, {r0 - lr}^			@ get calling r0 - lr
325	.endif
326	mov	r0, r0				@ ARMv5T and earlier require a nop
327						@ after ldm {}^
328	add	sp, sp, #\offset + PT_REGS_SIZE
329	movs	pc, lr				@ return & move spsr_svc into cpsr
3301:	bug	"Returning to usermode but unexpected PSR bits set?", \@
331#elif defined(CONFIG_CPU_V7M)
332	@ V7M restore.
333	@ Note that we don't need to do clrex here as clearing the local
334	@ monitor is part of the exception entry and exit sequence.
335	.if	\offset
336	add	sp, #\offset
337	.endif
338	v7m_exception_slow_exit ret_r0 = \fast
339#else
340	@ Thumb mode restore
341	mov	r2, sp
342	load_user_sp_lr r2, r3, \offset + S_SP	@ calling sp, lr
343	ldr	r1, [sp, #\offset + S_PSR]	@ get calling cpsr
344	ldr	lr, [sp, #\offset + S_PC]	@ get pc
345	add	sp, sp, #\offset + S_SP
346	tst	r1, #PSR_I_BIT | 0x0f
347	bne	1f
348	msr	spsr_cxsf, r1			@ save in spsr_svc
349
350	@ We must avoid clrex due to Cortex-A15 erratum #830321
351	strex	r1, r2, [sp]			@ clear the exclusive monitor
352
353	.if	\fast
354	ldmdb	sp, {r1 - r12}			@ get calling r1 - r12
355	.else
356	ldmdb	sp, {r0 - r12}			@ get calling r0 - r12
357	.endif
358	add	sp, sp, #PT_REGS_SIZE - S_SP
359	movs	pc, lr				@ return & move spsr_svc into cpsr
3601:	bug	"Returning to usermode but unexpected PSR bits set?", \@
361#endif	/* !CONFIG_THUMB2_KERNEL */
362	.endm
363
364/*
365 * Context tracking subsystem.  Used to instrument transitions
366 * between user and kernel mode.
367 */
368	.macro ct_user_exit, save = 1
369#ifdef CONFIG_CONTEXT_TRACKING_USER
370	.if	\save
371	stmdb   sp!, {r0-r3, ip, lr}
372	bl	user_exit_callable
373	ldmia	sp!, {r0-r3, ip, lr}
374	.else
375	bl	user_exit_callable
376	.endif
377#endif
378	.endm
379
380	.macro ct_user_enter, save = 1
381#ifdef CONFIG_CONTEXT_TRACKING_USER
382	.if	\save
383	stmdb   sp!, {r0-r3, ip, lr}
384	bl	user_enter_callable
385	ldmia	sp!, {r0-r3, ip, lr}
386	.else
387	bl	user_enter_callable
388	.endif
389#endif
390	.endm
391
392	.macro	invoke_syscall, table, nr, tmp, ret, reload=0
393#ifdef CONFIG_CPU_SPECTRE
394	mov	\tmp, \nr
395	cmp	\tmp, #NR_syscalls		@ check upper syscall limit
396	movcs	\tmp, #0
397	csdb
398	badr	lr, \ret			@ return address
399	.if	\reload
400	add	r1, sp, #S_R0 + S_OFF		@ pointer to regs
401	ldmiacc	r1, {r0 - r6}			@ reload r0-r6
402	stmiacc	sp, {r4, r5}			@ update stack arguments
403	.endif
404	ldrcc	pc, [\table, \tmp, lsl #2]	@ call sys_* routine
405#else
406	cmp	\nr, #NR_syscalls		@ check upper syscall limit
407	badr	lr, \ret			@ return address
408	.if	\reload
409	add	r1, sp, #S_R0 + S_OFF		@ pointer to regs
410	ldmiacc	r1, {r0 - r6}			@ reload r0-r6
411	stmiacc	sp, {r4, r5}			@ update stack arguments
412	.endif
413	ldrcc	pc, [\table, \nr, lsl #2]	@ call sys_* routine
414#endif
415	.endm
416
417/*
418 * These are the registers used in the syscall handler, and allow us to
419 * have in theory up to 7 arguments to a function - r0 to r6.
420 *
421 * r7 is reserved for the system call number for thumb mode.
422 *
423 * Note that tbl == why is intentional.
424 *
425 * We must set at least "tsk" and "why" when calling ret_with_reschedule.
426 */
427scno	.req	r7		@ syscall number
428tbl	.req	r8		@ syscall table pointer
429why	.req	r8		@ Linux syscall (!= 0)
430tsk	.req	r9		@ current thread_info
431
432	.macro	do_overflow_check, frame_size:req
433#ifdef CONFIG_VMAP_STACK
434	@
435	@ Test whether the SP has overflowed. Task and IRQ stacks are aligned
436	@ so that SP & BIT(THREAD_SIZE_ORDER + PAGE_SHIFT) should always be
437	@ zero.
438	@
439ARM(	tst	sp, #1 << (THREAD_SIZE_ORDER + PAGE_SHIFT)	)
440THUMB(	tst	r1, #1 << (THREAD_SIZE_ORDER + PAGE_SHIFT)	)
441THUMB(	it	ne						)
442	bne	.Lstack_overflow_check\@
443
444	.pushsection	.text
445.Lstack_overflow_check\@:
446	@
447	@ The stack pointer is not pointing to a valid vmap'ed stack, but it
448	@ may be pointing into the linear map instead, which may happen if we
449	@ are already running from the overflow stack. We cannot detect overflow
450	@ in such cases so just carry on.
451	@
452	str	ip, [r0, #12]			@ Stash IP on the mode stack
453	ldr_va	ip, high_memory			@ Start of VMALLOC space
454ARM(	cmp	sp, ip			)	@ SP in vmalloc space?
455THUMB(	cmp	r1, ip			)
456THUMB(	itt	lo			)
457	ldrlo	ip, [r0, #12]			@ Restore IP
458	blo	.Lout\@				@ Carry on
459
460THUMB(	sub	r1, sp, r1		)	@ Restore original R1
461THUMB(	sub	sp, r1			)	@ Restore original SP
462	add	sp, sp, #\frame_size		@ Undo svc_entry's SP change
463	b	__bad_stack			@ Handle VMAP stack overflow
464	.popsection
465.Lout\@:
466#endif
467	.endm
468