1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
4 *
5 * Vineetg: Aug 2009
6 * -"C" version of lowest level context switch asm macro called by schedular
7 * gcc doesn't generate the dward CFI info for hand written asm, hence can't
8 * backtrace out of it (e.g. tasks sleeping in kernel).
9 * So we cheat a bit by writing almost similar code in inline-asm.
10 * -This is a hacky way of doing things, but there is no other simple way.
11 * I don't want/intend to extend unwinding code to understand raw asm
12 */
13
14 #include <asm/asm-offsets.h>
15 #include <linux/sched.h>
16 #include <linux/sched/debug.h>
17
18 #define KSP_WORD_OFF ((TASK_THREAD + THREAD_KSP) / 4)
19
20 struct task_struct *__sched
__switch_to(struct task_struct * prev_task,struct task_struct * next_task)21 __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
22 {
23 unsigned int tmp;
24 unsigned int prev = (unsigned int)prev_task;
25 unsigned int next = (unsigned int)next_task;
26
27 __asm__ __volatile__(
28 /* FP/BLINK save generated by gcc (standard function prologue */
29 "st.a r13, [sp, -4] \n\t"
30 "st.a r14, [sp, -4] \n\t"
31 "st.a r15, [sp, -4] \n\t"
32 "st.a r16, [sp, -4] \n\t"
33 "st.a r17, [sp, -4] \n\t"
34 "st.a r18, [sp, -4] \n\t"
35 "st.a r19, [sp, -4] \n\t"
36 "st.a r20, [sp, -4] \n\t"
37 "st.a r21, [sp, -4] \n\t"
38 "st.a r22, [sp, -4] \n\t"
39 "st.a r23, [sp, -4] \n\t"
40 "st.a r24, [sp, -4] \n\t"
41 #ifndef CONFIG_ARC_CURR_IN_REG
42 "st.a r25, [sp, -4] \n\t"
43 #else
44 "sub sp, sp, 4 \n\t" /* usual r25 placeholder */
45 #endif
46
47 /* set ksp of outgoing task in tsk->thread.ksp */
48 #if KSP_WORD_OFF <= 255
49 "st.as sp, [%3, %1] \n\t"
50 #else
51 /*
52 * Workaround for NR_CPUS=4k
53 * %1 is bigger than 255 (S9 offset for st.as)
54 */
55 "add2 r24, %3, %1 \n\t"
56 "st sp, [r24] \n\t"
57 #endif
58
59 /*
60 * setup _current_task with incoming tsk.
61 * optionally, set r25 to that as well
62 * For SMP extra work to get to &_current_task[cpu]
63 * (open coded SET_CURR_TASK_ON_CPU)
64 */
65 #ifndef CONFIG_SMP
66 "st %2, [@_current_task] \n\t"
67 #else
68 "lr r24, [identity] \n\t"
69 "lsr r24, r24, 8 \n\t"
70 "bmsk r24, r24, 7 \n\t"
71 "add2 r24, @_current_task, r24 \n\t"
72 "st %2, [r24] \n\t"
73 #endif
74 #ifdef CONFIG_ARC_CURR_IN_REG
75 "mov r25, %2 \n\t"
76 #endif
77
78 /* get ksp of incoming task from tsk->thread.ksp */
79 "ld.as sp, [%2, %1] \n\t"
80
81 /* start loading it's CALLEE reg file */
82
83 #ifndef CONFIG_ARC_CURR_IN_REG
84 "ld.ab r25, [sp, 4] \n\t"
85 #else
86 "add sp, sp, 4 \n\t"
87 #endif
88 "ld.ab r24, [sp, 4] \n\t"
89 "ld.ab r23, [sp, 4] \n\t"
90 "ld.ab r22, [sp, 4] \n\t"
91 "ld.ab r21, [sp, 4] \n\t"
92 "ld.ab r20, [sp, 4] \n\t"
93 "ld.ab r19, [sp, 4] \n\t"
94 "ld.ab r18, [sp, 4] \n\t"
95 "ld.ab r17, [sp, 4] \n\t"
96 "ld.ab r16, [sp, 4] \n\t"
97 "ld.ab r15, [sp, 4] \n\t"
98 "ld.ab r14, [sp, 4] \n\t"
99 "ld.ab r13, [sp, 4] \n\t"
100
101 /* last (ret value) = prev : although for ARC it mov r0, r0 */
102 "mov %0, %3 \n\t"
103
104 /* FP/BLINK restore generated by gcc (standard func epilogue */
105
106 : "=r"(tmp)
107 : "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
108 : "blink"
109 );
110
111 return (struct task_struct *)tmp;
112 }
113