s390: add assembler macros for CPU alternatives

/* SPDX-License-Identifier: GPL-2.0 */

#ifndef _ASM_S390_ALTERNATIVE_ASM_H

#define _ASM_S390_ALTERNATIVE_ASM_H

#ifdef __ASSEMBLY__

/*

 * Check the length of an instruction sequence. The length may not be larger

 * than 254 bytes and it has to be divisible by 2.

 */

.macro alt_len_check start,end

	.if ( \end - \start ) > 254

	.error "cpu alternatives does not support instructions blocks > 254 bytes\n"

	.endif

	.if ( \end - \start ) % 2

	.error "cpu alternatives instructions length is odd\n"

	.endif

.endm

/*

 * 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 alt_entry orig_start, orig_end, alt_start, alt_end, feature

	.long	\orig_start - .

	.long	\alt_start - .

	.word	\feature

	.byte	\orig_end - \orig_start

	.byte	\alt_end - \alt_start

.endm

/*

 * Fill up @bytes with nops. The macro emits 6-byte nop instructions

 * for the bulk of the area, possibly followed by a 4-byte and/or

 * a 2-byte nop if the size of the area is not divisible by 6.

 */

.macro alt_pad_fill bytes

	.fill	( \bytes ) / 6, 6, 0xc0040000

	.fill	( \bytes ) % 6 / 4, 4, 0x47000000

	.fill	( \bytes ) % 6 % 4 / 2, 2, 0x0700

.endm

/*

 * Fill up @bytes with nops. If the number of bytes is larger

 * than 6, emit a jg instruction to branch over all nops, then

 * fill an area of size (@bytes - 6) with nop instructions.

 */

.macro alt_pad bytes

	.if ( \bytes > 0 )

	.if ( \bytes > 6 )

	jg	. + \bytes

	alt_pad_fill \bytes - 6

	.else

	alt_pad_fill \bytes

	.endif

	.endif

.endm

/*

 * Define an alternative between two instructions. If @feature is

 * present, early code in apply_alternatives() replaces @oldinstr with

 * @newinstr. ".skip" directive takes care of proper instruction padding

 * in case @newinstr is longer than @oldinstr.

 */

.macro ALTERNATIVE oldinstr, newinstr, feature

	.pushsection .altinstr_replacement,"ax"

770:	\newinstr

771:	.popsection

772:	\oldinstr

773:	alt_len_check 770b, 771b

	alt_len_check 772b, 773b

	alt_pad ( ( 771b - 770b ) - ( 773b - 772b ) )

774:	.pushsection .altinstructions,"a"

	alt_entry 772b, 774b, 770b, 771b, \feature

	.popsection

.endm

/*

 * Define an alternative between two instructions. If @feature is

 * present, early code in apply_alternatives() replaces @oldinstr with

 * @newinstr. ".skip" directive takes care of proper instruction padding

 * in case @newinstr is longer than @oldinstr.

 */

.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2

	.pushsection .altinstr_replacement,"ax"

770:	\newinstr1

771:	\newinstr2

772:	.popsection

773:	\oldinstr

774:	alt_len_check 770b, 771b

	alt_len_check 771b, 772b

	alt_len_check 773b, 774b

	.if ( 771b - 770b > 772b - 771b )

	alt_pad ( ( 771b - 770b ) - ( 774b - 773b ) )

	.else

	alt_pad ( ( 772b - 771b ) - ( 774b - 773b ) )

	.endif

775:	.pushsection .altinstructions,"a"

	alt_entry 773b, 775b, 770b, 771b,\feature1

	alt_entry 773b, 775b, 771b, 772b,\feature2

	.popsection

.endm

#endif	/*  __ASSEMBLY__  */

#endif /* _ASM_S390_ALTERNATIVE_ASM_H */