arch/loongarch/include/asm/alternative-asm.h

Source file repositories/reference/linux-study-clean/arch/loongarch/include/asm/alternative-asm.h

File Facts

System
Linux kernel
Corpus path
arch/loongarch/include/asm/alternative-asm.h
Extension
.h
Size
2088 bytes
Lines
83
Domain
Architecture Layer
Bucket
arch/loongarch
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

#ifndef _ASM_ALTERNATIVE_ASM_H
#define _ASM_ALTERNATIVE_ASM_H

#ifdef __ASSEMBLER__

#include <asm/asm.h>

/*
 * Issue one struct alt_instr descriptor entry (need to put it into
 * the section .altinstructions, see below). This entry contains
 * enough information for the alternatives patching code to patch an
 * instruction. See apply_alternatives().
 */
.macro altinstruction_entry orig alt feature orig_len alt_len
	.long \orig - .
	.long \alt - .
	.short \feature
	.byte \orig_len
	.byte \alt_len
.endm

/*
 * Define an alternative between two instructions. If @feature is
 * present, early code in apply_alternatives() replaces @oldinstr with
 * @newinstr. ".fill" directive takes care of proper instruction padding
 * in case @newinstr is longer than @oldinstr.
 */
.macro ALTERNATIVE oldinstr, newinstr, feature
140 :
	\oldinstr
141 :
	.fill - (((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)) / 4, 4, 0x03400000
142 :

	.pushsection .altinstructions, "a"
	altinstruction_entry 140b, 143f, \feature, 142b-140b, 144f-143f
	.popsection

	.subsection 1
143 :
	\newinstr
144 :
	.previous
.endm

#define old_len			(141b-140b)
#define new_len1		(144f-143f)
#define new_len2		(145f-144f)

#define alt_max_short(a, b)	((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))

/*
 * Same as ALTERNATIVE macro above but for two alternatives. If CPU
 * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
 * @feature2, it replaces @oldinstr with @feature2.
 */
.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
140 :
	\oldinstr
141 :
	.fill - ((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
		(alt_max_short(new_len1, new_len2) - (old_len)) / 4, 4, 0x03400000
142 :

	.pushsection .altinstructions, "a"
	altinstruction_entry 140b, 143f, \feature1, 142b-140b, 144f-143f, 142b-141b
	altinstruction_entry 140b, 144f, \feature2, 142b-140b, 145f-144f, 142b-141b
	.popsection

	.subsection 1
143 :
	\newinstr1
144 :
	\newinstr2
145 :
	.previous
.endm

#endif  /*  __ASSEMBLER__  */

#endif /* _ASM_ALTERNATIVE_ASM_H */

Annotation

Implementation Notes