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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/arch/hexagon/kernel/vm_switch.S
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/* SPDX-License-Identifier: GPL-2.0-only */

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/*

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 * Context switch support for Hexagon

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 *

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 * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.

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 */

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#include <asm/asm-offsets.h>

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.text

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/*

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 * The register used as a fast-path thread information pointer

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 * is determined as a kernel configuration option.  If it happens

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 * to be a callee-save register, we're going to be saving and

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 * restoring it twice here.

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 *

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 * This code anticipates a revised ABI where R20-23 are added

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 * to the set of callee-save registers, but this should be

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 * backward compatible to legacy tools.

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 */

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/*

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 *	void switch_to(struct task_struct *prev,

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 *		struct task_struct *next, struct task_struct *last);

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 */

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	.p2align 2

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	.globl __switch_to

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	.type	__switch_to, @function

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/*

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 * When we exit the wormhole, we need to store the previous task

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 * in the new R0's pointer.  Technically it should be R2, but they should

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 * be the same; seems like a legacy thing.  In short, don't butcher

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 * R0, let it go back out unmolested.

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 */

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__switch_to:

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	/*

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	 * Push callee-saves onto "prev" stack.

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	 * Here, we're sneaky because the LR and FP

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	 * storage of the thread_stack structure

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	 * is automagically allocated by allocframe,

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	 * so we pass struct size less 8.

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	 */

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	allocframe(#(_SWITCH_STACK_SIZE - 8));

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	memd(R29+#(_SWITCH_R2726))=R27:26;

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	memd(R29+#(_SWITCH_R2524))=R25:24;

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	memd(R29+#(_SWITCH_R2322))=R23:22;

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	memd(R29+#(_SWITCH_R2120))=R21:20;

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	memd(R29+#(_SWITCH_R1918))=R19:18;

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	memd(R29+#(_SWITCH_R1716))=R17:16;

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	/* Stash thread_info pointer in task_struct */

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	memw(R0+#_TASK_THREAD_INFO) = THREADINFO_REG;

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	memw(R0 +#(_TASK_STRUCT_THREAD + _THREAD_STRUCT_SWITCH_SP)) = R29;

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	/* Switch to "next" stack and restore callee saves from there */

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	R29 = memw(R1 + #(_TASK_STRUCT_THREAD + _THREAD_STRUCT_SWITCH_SP));

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	{

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	    R27:26 = memd(R29+#(_SWITCH_R2726));

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	    R25:24 = memd(R29+#(_SWITCH_R2524));

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	}

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	{

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	    R23:22 = memd(R29+#(_SWITCH_R2322));

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	    R21:20 = memd(R29+#(_SWITCH_R2120));

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	}

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	{

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	    R19:18 = memd(R29+#(_SWITCH_R1918));

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	    R17:16 = memd(R29+#(_SWITCH_R1716));

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	}

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	{

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	    /* THREADINFO_REG is currently one of the callee-saved regs

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	     * above, and so be sure to re-load it last.

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	     */

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	    THREADINFO_REG = memw(R1 + #_TASK_THREAD_INFO);

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	    R31:30 = memd(R29+#_SWITCH_FP);

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	}

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	{

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	    R29 = add(R29,#_SWITCH_STACK_SIZE);

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	    jumpr R31;

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	}

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	.size	__switch_to, .-__switch_to

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