xref: /openbmc/linux/arch/riscv/kernel/entry.S (revision 812f77b749a8ae11f58dacf0d3ed65e7ede47458)
1/*
2 * Copyright (C) 2012 Regents of the University of California
3 * Copyright (C) 2017 SiFive
4 *
5 *   This program is free software; you can redistribute it and/or
6 *   modify it under the terms of the GNU General Public License
7 *   as published by the Free Software Foundation, version 2.
8 *
9 *   This program is distributed in the hope that it will be useful,
10 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
11 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12 *   GNU General Public License for more details.
13 */
14
15#include <linux/init.h>
16#include <linux/linkage.h>
17
18#include <asm/asm.h>
19#include <asm/csr.h>
20#include <asm/unistd.h>
21#include <asm/thread_info.h>
22#include <asm/asm-offsets.h>
23
24	.text
25	.altmacro
26
27/*
28 * Prepares to enter a system call or exception by saving all registers to the
29 * stack.
30 */
31	.macro SAVE_ALL
32	LOCAL _restore_kernel_tpsp
33	LOCAL _save_context
34
35	/*
36	 * If coming from userspace, preserve the user thread pointer and load
37	 * the kernel thread pointer.  If we came from the kernel, sscratch
38	 * will contain 0, and we should continue on the current TP.
39	 */
40	csrrw tp, sscratch, tp
41	bnez tp, _save_context
42
43_restore_kernel_tpsp:
44	csrr tp, sscratch
45	REG_S sp, TASK_TI_KERNEL_SP(tp)
46_save_context:
47	REG_S sp, TASK_TI_USER_SP(tp)
48	REG_L sp, TASK_TI_KERNEL_SP(tp)
49	addi sp, sp, -(PT_SIZE_ON_STACK)
50	REG_S x1,  PT_RA(sp)
51	REG_S x3,  PT_GP(sp)
52	REG_S x5,  PT_T0(sp)
53	REG_S x6,  PT_T1(sp)
54	REG_S x7,  PT_T2(sp)
55	REG_S x8,  PT_S0(sp)
56	REG_S x9,  PT_S1(sp)
57	REG_S x10, PT_A0(sp)
58	REG_S x11, PT_A1(sp)
59	REG_S x12, PT_A2(sp)
60	REG_S x13, PT_A3(sp)
61	REG_S x14, PT_A4(sp)
62	REG_S x15, PT_A5(sp)
63	REG_S x16, PT_A6(sp)
64	REG_S x17, PT_A7(sp)
65	REG_S x18, PT_S2(sp)
66	REG_S x19, PT_S3(sp)
67	REG_S x20, PT_S4(sp)
68	REG_S x21, PT_S5(sp)
69	REG_S x22, PT_S6(sp)
70	REG_S x23, PT_S7(sp)
71	REG_S x24, PT_S8(sp)
72	REG_S x25, PT_S9(sp)
73	REG_S x26, PT_S10(sp)
74	REG_S x27, PT_S11(sp)
75	REG_S x28, PT_T3(sp)
76	REG_S x29, PT_T4(sp)
77	REG_S x30, PT_T5(sp)
78	REG_S x31, PT_T6(sp)
79
80	/*
81	 * Disable FPU to detect illegal usage of
82	 * floating point in kernel space
83	 */
84	li t0, SR_FS
85
86	REG_L s0, TASK_TI_USER_SP(tp)
87	csrrc s1, sstatus, t0
88	csrr s2, sepc
89	csrr s3, sbadaddr
90	csrr s4, scause
91	csrr s5, sscratch
92	REG_S s0, PT_SP(sp)
93	REG_S s1, PT_SSTATUS(sp)
94	REG_S s2, PT_SEPC(sp)
95	REG_S s3, PT_SBADADDR(sp)
96	REG_S s4, PT_SCAUSE(sp)
97	REG_S s5, PT_TP(sp)
98	.endm
99
100/*
101 * Prepares to return from a system call or exception by restoring all
102 * registers from the stack.
103 */
104	.macro RESTORE_ALL
105	REG_L a0, PT_SSTATUS(sp)
106	REG_L a2, PT_SEPC(sp)
107	csrw sstatus, a0
108	csrw sepc, a2
109
110	REG_L x1,  PT_RA(sp)
111	REG_L x3,  PT_GP(sp)
112	REG_L x4,  PT_TP(sp)
113	REG_L x5,  PT_T0(sp)
114	REG_L x6,  PT_T1(sp)
115	REG_L x7,  PT_T2(sp)
116	REG_L x8,  PT_S0(sp)
117	REG_L x9,  PT_S1(sp)
118	REG_L x10, PT_A0(sp)
119	REG_L x11, PT_A1(sp)
120	REG_L x12, PT_A2(sp)
121	REG_L x13, PT_A3(sp)
122	REG_L x14, PT_A4(sp)
123	REG_L x15, PT_A5(sp)
124	REG_L x16, PT_A6(sp)
125	REG_L x17, PT_A7(sp)
126	REG_L x18, PT_S2(sp)
127	REG_L x19, PT_S3(sp)
128	REG_L x20, PT_S4(sp)
129	REG_L x21, PT_S5(sp)
130	REG_L x22, PT_S6(sp)
131	REG_L x23, PT_S7(sp)
132	REG_L x24, PT_S8(sp)
133	REG_L x25, PT_S9(sp)
134	REG_L x26, PT_S10(sp)
135	REG_L x27, PT_S11(sp)
136	REG_L x28, PT_T3(sp)
137	REG_L x29, PT_T4(sp)
138	REG_L x30, PT_T5(sp)
139	REG_L x31, PT_T6(sp)
140
141	REG_L x2,  PT_SP(sp)
142	.endm
143
144ENTRY(handle_exception)
145	SAVE_ALL
146
147	/*
148	 * Set sscratch register to 0, so that if a recursive exception
149	 * occurs, the exception vector knows it came from the kernel
150	 */
151	csrw sscratch, x0
152
153	/* Load the global pointer */
154.option push
155.option norelax
156	la gp, __global_pointer$
157.option pop
158
159	la ra, ret_from_exception
160	/*
161	 * MSB of cause differentiates between
162	 * interrupts and exceptions
163	 */
164	bge s4, zero, 1f
165
166	/* Handle interrupts */
167	slli a0, s4, 1
168	srli a0, a0, 1
169	move a1, sp /* pt_regs */
170	tail do_IRQ
1711:
172	/* Handle syscalls */
173	li t0, EXC_SYSCALL
174	beq s4, t0, handle_syscall
175
176	/* Handle other exceptions */
177	slli t0, s4, RISCV_LGPTR
178	la t1, excp_vect_table
179	la t2, excp_vect_table_end
180	move a0, sp /* pt_regs */
181	add t0, t1, t0
182	/* Check if exception code lies within bounds */
183	bgeu t0, t2, 1f
184	REG_L t0, 0(t0)
185	jr t0
1861:
187	tail do_trap_unknown
188
189handle_syscall:
190	 /* save the initial A0 value (needed in signal handlers) */
191	REG_S a0, PT_ORIG_A0(sp)
192	/*
193	 * Advance SEPC to avoid executing the original
194	 * scall instruction on sret
195	 */
196	addi s2, s2, 0x4
197	REG_S s2, PT_SEPC(sp)
198	/* System calls run with interrupts enabled */
199	csrs sstatus, SR_IE
200	/* Trace syscalls, but only if requested by the user. */
201	REG_L t0, TASK_TI_FLAGS(tp)
202	andi t0, t0, _TIF_SYSCALL_TRACE
203	bnez t0, handle_syscall_trace_enter
204check_syscall_nr:
205	/* Check to make sure we don't jump to a bogus syscall number. */
206	li t0, __NR_syscalls
207	la s0, sys_ni_syscall
208	/* Syscall number held in a7 */
209	bgeu a7, t0, 1f
210	la s0, sys_call_table
211	slli t0, a7, RISCV_LGPTR
212	add s0, s0, t0
213	REG_L s0, 0(s0)
2141:
215	jalr s0
216
217ret_from_syscall:
218	/* Set user a0 to kernel a0 */
219	REG_S a0, PT_A0(sp)
220	/* Trace syscalls, but only if requested by the user. */
221	REG_L t0, TASK_TI_FLAGS(tp)
222	andi t0, t0, _TIF_SYSCALL_TRACE
223	bnez t0, handle_syscall_trace_exit
224
225ret_from_exception:
226	REG_L s0, PT_SSTATUS(sp)
227	csrc sstatus, SR_IE
228	andi s0, s0, SR_PS
229	bnez s0, restore_all
230
231resume_userspace:
232	/* Interrupts must be disabled here so flags are checked atomically */
233	REG_L s0, TASK_TI_FLAGS(tp) /* current_thread_info->flags */
234	andi s1, s0, _TIF_WORK_MASK
235	bnez s1, work_pending
236
237	/* Save unwound kernel stack pointer in thread_info */
238	addi s0, sp, PT_SIZE_ON_STACK
239	REG_S s0, TASK_TI_KERNEL_SP(tp)
240
241	/*
242	 * Save TP into sscratch, so we can find the kernel data structures
243	 * again.
244	 */
245	csrw sscratch, tp
246
247restore_all:
248	RESTORE_ALL
249	sret
250
251work_pending:
252	/* Enter slow path for supplementary processing */
253	la ra, ret_from_exception
254	andi s1, s0, _TIF_NEED_RESCHED
255	bnez s1, work_resched
256work_notifysig:
257	/* Handle pending signals and notify-resume requests */
258	csrs sstatus, SR_IE /* Enable interrupts for do_notify_resume() */
259	move a0, sp /* pt_regs */
260	move a1, s0 /* current_thread_info->flags */
261	tail do_notify_resume
262work_resched:
263	tail schedule
264
265/* Slow paths for ptrace. */
266handle_syscall_trace_enter:
267	move a0, sp
268	call do_syscall_trace_enter
269	REG_L a0, PT_A0(sp)
270	REG_L a1, PT_A1(sp)
271	REG_L a2, PT_A2(sp)
272	REG_L a3, PT_A3(sp)
273	REG_L a4, PT_A4(sp)
274	REG_L a5, PT_A5(sp)
275	REG_L a6, PT_A6(sp)
276	REG_L a7, PT_A7(sp)
277	j check_syscall_nr
278handle_syscall_trace_exit:
279	move a0, sp
280	call do_syscall_trace_exit
281	j ret_from_exception
282
283END(handle_exception)
284
285ENTRY(ret_from_fork)
286	la ra, ret_from_exception
287	tail schedule_tail
288ENDPROC(ret_from_fork)
289
290ENTRY(ret_from_kernel_thread)
291	call schedule_tail
292	/* Call fn(arg) */
293	la ra, ret_from_exception
294	move a0, s1
295	jr s0
296ENDPROC(ret_from_kernel_thread)
297
298
299/*
300 * Integer register context switch
301 * The callee-saved registers must be saved and restored.
302 *
303 *   a0: previous task_struct (must be preserved across the switch)
304 *   a1: next task_struct
305 *
306 * The value of a0 and a1 must be preserved by this function, as that's how
307 * arguments are passed to schedule_tail.
308 */
309ENTRY(__switch_to)
310	/* Save context into prev->thread */
311	li    a4,  TASK_THREAD_RA
312	add   a3, a0, a4
313	add   a4, a1, a4
314	REG_S ra,  TASK_THREAD_RA_RA(a3)
315	REG_S sp,  TASK_THREAD_SP_RA(a3)
316	REG_S s0,  TASK_THREAD_S0_RA(a3)
317	REG_S s1,  TASK_THREAD_S1_RA(a3)
318	REG_S s2,  TASK_THREAD_S2_RA(a3)
319	REG_S s3,  TASK_THREAD_S3_RA(a3)
320	REG_S s4,  TASK_THREAD_S4_RA(a3)
321	REG_S s5,  TASK_THREAD_S5_RA(a3)
322	REG_S s6,  TASK_THREAD_S6_RA(a3)
323	REG_S s7,  TASK_THREAD_S7_RA(a3)
324	REG_S s8,  TASK_THREAD_S8_RA(a3)
325	REG_S s9,  TASK_THREAD_S9_RA(a3)
326	REG_S s10, TASK_THREAD_S10_RA(a3)
327	REG_S s11, TASK_THREAD_S11_RA(a3)
328	/* Restore context from next->thread */
329	REG_L ra,  TASK_THREAD_RA_RA(a4)
330	REG_L sp,  TASK_THREAD_SP_RA(a4)
331	REG_L s0,  TASK_THREAD_S0_RA(a4)
332	REG_L s1,  TASK_THREAD_S1_RA(a4)
333	REG_L s2,  TASK_THREAD_S2_RA(a4)
334	REG_L s3,  TASK_THREAD_S3_RA(a4)
335	REG_L s4,  TASK_THREAD_S4_RA(a4)
336	REG_L s5,  TASK_THREAD_S5_RA(a4)
337	REG_L s6,  TASK_THREAD_S6_RA(a4)
338	REG_L s7,  TASK_THREAD_S7_RA(a4)
339	REG_L s8,  TASK_THREAD_S8_RA(a4)
340	REG_L s9,  TASK_THREAD_S9_RA(a4)
341	REG_L s10, TASK_THREAD_S10_RA(a4)
342	REG_L s11, TASK_THREAD_S11_RA(a4)
343	/* Swap the CPU entry around. */
344	lw a3, TASK_TI_CPU(a0)
345	lw a4, TASK_TI_CPU(a1)
346	sw a3, TASK_TI_CPU(a1)
347	sw a4, TASK_TI_CPU(a0)
348#if TASK_TI != 0
349#error "TASK_TI != 0: tp will contain a 'struct thread_info', not a 'struct task_struct' so get_current() won't work."
350	addi tp, a1, TASK_TI
351#else
352	move tp, a1
353#endif
354	ret
355ENDPROC(__switch_to)
356
357ENTRY(__fstate_save)
358	li  a2,  TASK_THREAD_F0
359	add a0, a0, a2
360	li t1, SR_FS
361	csrs sstatus, t1
362	frcsr t0
363	fsd f0,  TASK_THREAD_F0_F0(a0)
364	fsd f1,  TASK_THREAD_F1_F0(a0)
365	fsd f2,  TASK_THREAD_F2_F0(a0)
366	fsd f3,  TASK_THREAD_F3_F0(a0)
367	fsd f4,  TASK_THREAD_F4_F0(a0)
368	fsd f5,  TASK_THREAD_F5_F0(a0)
369	fsd f6,  TASK_THREAD_F6_F0(a0)
370	fsd f7,  TASK_THREAD_F7_F0(a0)
371	fsd f8,  TASK_THREAD_F8_F0(a0)
372	fsd f9,  TASK_THREAD_F9_F0(a0)
373	fsd f10, TASK_THREAD_F10_F0(a0)
374	fsd f11, TASK_THREAD_F11_F0(a0)
375	fsd f12, TASK_THREAD_F12_F0(a0)
376	fsd f13, TASK_THREAD_F13_F0(a0)
377	fsd f14, TASK_THREAD_F14_F0(a0)
378	fsd f15, TASK_THREAD_F15_F0(a0)
379	fsd f16, TASK_THREAD_F16_F0(a0)
380	fsd f17, TASK_THREAD_F17_F0(a0)
381	fsd f18, TASK_THREAD_F18_F0(a0)
382	fsd f19, TASK_THREAD_F19_F0(a0)
383	fsd f20, TASK_THREAD_F20_F0(a0)
384	fsd f21, TASK_THREAD_F21_F0(a0)
385	fsd f22, TASK_THREAD_F22_F0(a0)
386	fsd f23, TASK_THREAD_F23_F0(a0)
387	fsd f24, TASK_THREAD_F24_F0(a0)
388	fsd f25, TASK_THREAD_F25_F0(a0)
389	fsd f26, TASK_THREAD_F26_F0(a0)
390	fsd f27, TASK_THREAD_F27_F0(a0)
391	fsd f28, TASK_THREAD_F28_F0(a0)
392	fsd f29, TASK_THREAD_F29_F0(a0)
393	fsd f30, TASK_THREAD_F30_F0(a0)
394	fsd f31, TASK_THREAD_F31_F0(a0)
395	sw t0, TASK_THREAD_FCSR_F0(a0)
396	csrc sstatus, t1
397	ret
398ENDPROC(__fstate_save)
399
400ENTRY(__fstate_restore)
401	li  a2,  TASK_THREAD_F0
402	add a0, a0, a2
403	li t1, SR_FS
404	lw t0, TASK_THREAD_FCSR_F0(a0)
405	csrs sstatus, t1
406	fld f0,  TASK_THREAD_F0_F0(a0)
407	fld f1,  TASK_THREAD_F1_F0(a0)
408	fld f2,  TASK_THREAD_F2_F0(a0)
409	fld f3,  TASK_THREAD_F3_F0(a0)
410	fld f4,  TASK_THREAD_F4_F0(a0)
411	fld f5,  TASK_THREAD_F5_F0(a0)
412	fld f6,  TASK_THREAD_F6_F0(a0)
413	fld f7,  TASK_THREAD_F7_F0(a0)
414	fld f8,  TASK_THREAD_F8_F0(a0)
415	fld f9,  TASK_THREAD_F9_F0(a0)
416	fld f10, TASK_THREAD_F10_F0(a0)
417	fld f11, TASK_THREAD_F11_F0(a0)
418	fld f12, TASK_THREAD_F12_F0(a0)
419	fld f13, TASK_THREAD_F13_F0(a0)
420	fld f14, TASK_THREAD_F14_F0(a0)
421	fld f15, TASK_THREAD_F15_F0(a0)
422	fld f16, TASK_THREAD_F16_F0(a0)
423	fld f17, TASK_THREAD_F17_F0(a0)
424	fld f18, TASK_THREAD_F18_F0(a0)
425	fld f19, TASK_THREAD_F19_F0(a0)
426	fld f20, TASK_THREAD_F20_F0(a0)
427	fld f21, TASK_THREAD_F21_F0(a0)
428	fld f22, TASK_THREAD_F22_F0(a0)
429	fld f23, TASK_THREAD_F23_F0(a0)
430	fld f24, TASK_THREAD_F24_F0(a0)
431	fld f25, TASK_THREAD_F25_F0(a0)
432	fld f26, TASK_THREAD_F26_F0(a0)
433	fld f27, TASK_THREAD_F27_F0(a0)
434	fld f28, TASK_THREAD_F28_F0(a0)
435	fld f29, TASK_THREAD_F29_F0(a0)
436	fld f30, TASK_THREAD_F30_F0(a0)
437	fld f31, TASK_THREAD_F31_F0(a0)
438	fscsr t0
439	csrc sstatus, t1
440	ret
441ENDPROC(__fstate_restore)
442
443
444	.section ".rodata"
445	/* Exception vector table */
446ENTRY(excp_vect_table)
447	RISCV_PTR do_trap_insn_misaligned
448	RISCV_PTR do_trap_insn_fault
449	RISCV_PTR do_trap_insn_illegal
450	RISCV_PTR do_trap_break
451	RISCV_PTR do_trap_load_misaligned
452	RISCV_PTR do_trap_load_fault
453	RISCV_PTR do_trap_store_misaligned
454	RISCV_PTR do_trap_store_fault
455	RISCV_PTR do_trap_ecall_u /* system call, gets intercepted */
456	RISCV_PTR do_trap_ecall_s
457	RISCV_PTR do_trap_unknown
458	RISCV_PTR do_trap_ecall_m
459	RISCV_PTR do_page_fault   /* instruction page fault */
460	RISCV_PTR do_page_fault   /* load page fault */
461	RISCV_PTR do_trap_unknown
462	RISCV_PTR do_page_fault   /* store page fault */
463excp_vect_table_end:
464END(excp_vect_table)
465