s390: add assembler macros for CPU alternatives

[ 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>

diff --git a/arch/s390/include/asm/alternative-asm.h b/arch/s390/include/asm/alternative-asm.h
new file mode 100644 (file)
index 0000000..955d620
--- /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 */