4.9-stable review patch. If anyone has any objections, please let me know.
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From: Martin Schwidefsky schwidefsky@de.ibm.com
[ Upstream commit fba9eb7946251d6e420df3bdf7bc45195be7be9a ]
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/s390/include/asm/alternative-asm.h | 108 ++++++++++++++++++++++++++++++++ 1 file changed, 108 insertions(+) create mode 100644 arch/s390/include/asm/alternative-asm.h
--- /dev/null +++ b/arch/s390/include/asm/alternative-asm.h @@ -0,0 +1,108 @@ +/* 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 */