[Xen-devel] [PATCH v2 1/2] x86: support 2- and 3-way alternatives

["Jan Beulich" <JBeulich@xxxxxxxx>]

Parts taken from Linux, but implementing the ALTERNATIVE*() macros
recursively to avoid needless redundancy.

Also make the .discard section non-writable (we might even consider
dropping its alloc flag too) and limit the pushing and popping of
sections.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/include/asm-x86/alternative.h
+++ b/xen/include/asm-x86/alternative.h
@@ -46,18 +46,28 @@ extern void alternative_instructions(voi
 #define ALTINSTR_REPLACEMENT(newinstr, feature, number) /* replacement */     \
         b_replacement(number)":\n\t" newinstr "\n" e_replacement(number) 
":\n\t"
 
+#define ALTERNATIVE_N(newinstr, feature, number)       \
+        ".pushsection .altinstructions,\"a\"\n"                \
+        ALTINSTR_ENTRY(feature, number)                        \
+        ".section .discard,\"a\",@progbits\n"          \
+        DISCARD_ENTRY(number)                          \
+        ".section .altinstr_replacement, \"ax\"\n"     \
+        ALTINSTR_REPLACEMENT(newinstr, feature, number)        \
+        ".popsection\n"
+
 /* alternative assembly primitive: */
-#define ALTERNATIVE(oldinstr, newinstr, feature)                        \
-        OLDINSTR(oldinstr)                                              \
-        ".pushsection .altinstructions,\"a\"\n"                         \
-        ALTINSTR_ENTRY(feature, 1)                                      \
-        ".popsection\n"                                                 \
-        ".pushsection .discard,\"aw\",@progbits\n"                      \
-        DISCARD_ENTRY(1)                                                \
-        ".popsection\n"                                                 \
-        ".pushsection .altinstr_replacement, \"ax\"\n"                  \
-        ALTINSTR_REPLACEMENT(newinstr, feature, 1)                      \
-        ".popsection"
+#define ALTERNATIVE(oldinstr, newinstr, feature)                         \
+        OLDINSTR(oldinstr)                                               \
+       ALTERNATIVE_N(newinstr, feature, 1)
+
+#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
+        ALTERNATIVE(oldinstr, newinstr1, feature1)                       \
+       ALTERNATIVE_N(newinstr2, feature2, 2)
+
+#define ALTERNATIVE_3(oldinstr, newinstr1, feature1, newinstr2, feature2, \
+                     newinstr3, feature3)                                \
+        ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
+       ALTERNATIVE_N(newinstr3, feature3, 3)
 
 /*
  * Alternative instructions for different CPU types or capabilities.
@@ -93,6 +103,37 @@ extern void alternative_instructions(voi
        asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
                      : output : input)
 
+/*
+ * This is similar to alternative_io. But it has two features and
+ * respective instructions.
+ *
+ * If CPU has feature2, newinstr2 is used.
+ * Otherwise, if CPU has feature1, newinstr1 is used.
+ * Otherwise, oldinstr is used.
+ */
+#define alternative_io_2(oldinstr, newinstr1, feature1, newinstr2,     \
+                        feature2, output, input...)                    \
+       asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1,       \
+                                  newinstr2, feature2)                 \
+                    : output : input)
+
+/*
+ * This is similar to alternative_io. But it has three features and
+ * respective instructions.
+ *
+ * If CPU has feature3, newinstr3 is used.
+ * Otherwise, if CPU has feature2, newinstr2 is used.
+ * Otherwise, if CPU has feature1, newinstr1 is used.
+ * Otherwise, oldinstr is used.
+ */
+#define alternative_io_3(oldinstr, newinstr1, feature1, newinstr2,     \
+                        feature2, newinstr3, feature3, output,         \
+                        input...)                                      \
+       asm volatile(ALTERNATIVE_3(oldinstr, newinstr1, feature1,       \
+                                  newinstr2, feature2, newinstr3,      \
+                                  feature3)                            \
+                    : output : input)
+
 /* Use this macro(s) if you need more than one output parameter. */
 #define ASM_OUTPUT2(a...) a

Attachment: x86-alternative-2-3.patch
Description: Text document

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