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