ctx_sw.c (3210B)
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 20struct task_struct *__sched 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}