[RFC PATCH 3/4] x86/alternatives: Add an ALTERNATIVE_3() macro

Borislav Petkov
2018-12-11T22:23:37Z

From: Borislav Petkov <bp@suse.de>

Similar to ALTERNATIVE_2(), ALTERNATIVE_3() selects between 3 possible
variants. Will be used for adding RDTSCP to the rdtsc_ordered()
alternatives.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/include/asm/alternative.h | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 8d38b296a18a..f24d111f366b 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -115,6 +115,16 @@ static inline int alternatives_text_reserved(void *start, void *end)
"(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n" \
alt_end_marker ":\n"

+#define OLDINSTR_3(oldinsn, n1, n2, n3) \
+ "# ALT: oldinstr3\n" \
+ "661:\n\t" oldinsn "\n662:\n" \
+ "# ALT: padding3\n" \
+ ".skip -((" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3)) \
+ " - (" alt_slen ")) > 0) * " \
+ "(" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3)) \
+ " - (" alt_slen ")), 0x90\n" \
+ alt_end_marker ":\n"
+
#define ALTINSTR_ENTRY(feature, num) \
" .long 661b - .\n" /* label */ \
" .long " b_replacement(num)"f - .\n" /* new instruction */ \
@@ -148,6 +158,19 @@ static inline int alternatives_text_reserved(void *start, void *end)
ALTINSTR_REPLACEMENT(newinstr2, feature2, 2) \
".popsection\n"

+#define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \
+ OLDINSTR_3(oldinsn, 1, 2, 3) \
+ ".pushsection .altinstructions,\"a\"\n" \
+ ALTINSTR_ENTRY(feat1, 1) \
+ ALTINSTR_ENTRY(feat2, 2) \
+ ALTINSTR_ENTRY(feat3, 3) \
+ ".popsection\n" \
+ ".pushsection .altinstr_replacement, \"ax\"\n" \
+ ALTINSTR_REPLACEMENT(newinsn1, feat1, 1) \
+ ALTINSTR_REPLACEMENT(newinsn2, feat2, 2) \
+ ALTINSTR_REPLACEMENT(newinsn3, feat3, 3) \
+ ".popsection\n"
+
/*
* Alternative instructions for different CPU types or capabilities.
*
--
2.19.1