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s390: add assembler macros for CPU alternatives
Add a header with macros usable in assembler files to emit alternative
code sequences. It works analog to the alternatives for inline assmeblies
in C files, with the same restrictions and capabilities.
The syntax is
ALTERNATIVE "<default instructions sequence>", \
"<alternative instructions sequence>", \
"<features-bit>"
and
ALTERNATIVE_2 "<default instructions sequence>", \
"<alternative instructions sqeuence #1>", \
"<feature-bit #1>",
"<alternative instructions sqeuence #2>", \
"<feature-bit #2>"
Reviewed-by: Vasily Gorbik <gor@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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arch/s390/include/asm/alternative-asm.h
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arch/s390/include/asm/alternative-asm.h
···
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/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_S390_ALTERNATIVE_ASM_H
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#define _ASM_S390_ALTERNATIVE_ASM_H
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#ifdef __ASSEMBLY__
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/*
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* Check the length of an instruction sequence. The length may not be larger
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* than 254 bytes and it has to be divisible by 2.
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*/
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.macro alt_len_check start,end
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.if ( \end - \start ) > 254
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.error "cpu alternatives does not support instructions blocks > 254 bytes\n"
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.endif
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.if ( \end - \start ) % 2
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.error "cpu alternatives instructions length is odd\n"
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.endif
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.endm
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/*
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* Issue one struct alt_instr descriptor entry (need to put it into
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* the section .altinstructions, see below). This entry contains
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* enough information for the alternatives patching code to patch an
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* instruction. See apply_alternatives().
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*/
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.macro alt_entry orig_start, orig_end, alt_start, alt_end, feature
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.long \orig_start - .
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.long \alt_start - .
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.word \feature
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.byte \orig_end - \orig_start
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.byte \alt_end - \alt_start
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.endm
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/*
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* Fill up @bytes with nops. The macro emits 6-byte nop instructions
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* for the bulk of the area, possibly followed by a 4-byte and/or
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* a 2-byte nop if the size of the area is not divisible by 6.
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*/
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.macro alt_pad_fill bytes
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.fill ( \bytes ) / 6, 6, 0xc0040000
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.fill ( \bytes ) % 6 / 4, 4, 0x47000000
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.fill ( \bytes ) % 6 % 4 / 2, 2, 0x0700
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.endm
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/*
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* Fill up @bytes with nops. If the number of bytes is larger
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* than 6, emit a jg instruction to branch over all nops, then
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* fill an area of size (@bytes - 6) with nop instructions.
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*/
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.macro alt_pad bytes
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.if ( \bytes > 0 )
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.if ( \bytes > 6 )
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jg . + \bytes
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alt_pad_fill \bytes - 6
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.else
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alt_pad_fill \bytes
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.endif
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.endif
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.endm
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/*
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* Define an alternative between two instructions. If @feature is
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* present, early code in apply_alternatives() replaces @oldinstr with
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* @newinstr. ".skip" directive takes care of proper instruction padding
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* in case @newinstr is longer than @oldinstr.
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*/
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.macro ALTERNATIVE oldinstr, newinstr, feature
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.pushsection .altinstr_replacement,"ax"
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770: \newinstr
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771: .popsection
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772: \oldinstr
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773: alt_len_check 770b, 771b
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alt_len_check 772b, 773b
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alt_pad ( ( 771b - 770b ) - ( 773b - 772b ) )
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774: .pushsection .altinstructions,"a"
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alt_entry 772b, 774b, 770b, 771b, \feature
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.popsection
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.endm
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/*
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* Define an alternative between two instructions. If @feature is
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* present, early code in apply_alternatives() replaces @oldinstr with
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* @newinstr. ".skip" directive takes care of proper instruction padding
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* in case @newinstr is longer than @oldinstr.
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*/
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.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
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.pushsection .altinstr_replacement,"ax"
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770: \newinstr1
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771: \newinstr2
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772: .popsection
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773: \oldinstr
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774: alt_len_check 770b, 771b
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alt_len_check 771b, 772b
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alt_len_check 773b, 774b
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.if ( 771b - 770b > 772b - 771b )
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alt_pad ( ( 771b - 770b ) - ( 774b - 773b ) )
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.else
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alt_pad ( ( 772b - 771b ) - ( 774b - 773b ) )
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.endif
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775: .pushsection .altinstructions,"a"
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alt_entry 773b, 775b, 770b, 771b,\feature1
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alt_entry 773b, 775b, 771b, 772b,\feature2
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.popsection
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.endm
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_S390_ALTERNATIVE_ASM_H */