x86/alternatives: mark .altinstructions r/w

Forever since the introduction of the .priv member it has been wrong to
record the section as r/o.

.alt_call_sites, otoh, is legitimately r/o, hence
__alt_call_sites_{start,end}[] would better reflect that.

Fixes: 4008c71d7a ("x86/alt: Support for automatic padding calculations")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger@xenproject.org>

xen/arch/x86/alternative.c

@@ -464,7 +464,7 @@ static unsigned int __initdata alt_todo;
 static unsigned int __initdata alt_done;
 
 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
-extern struct alt_call __alt_call_sites_start[], __alt_call_sites_end[];
+extern const struct alt_call __alt_call_sites_start[], __alt_call_sites_end[];
 
 /*
  * At boot time, we patch alternatives in NMI context.  This means that the

xen/arch/x86/include/asm/alternative-asm.h

@@ -59,7 +59,7 @@
 .macro ALTERNATIVE oldinstr, newinstr, feature
     decl_orig(\oldinstr, repl_len(1) - orig_len)
 
-    .pushsection .altinstructions, "a", @progbits
+    .pushsection .altinstructions, "aw", @progbits
     altinstruction_entry .L\@_orig_s, .L\@_repl_s1, \feature, \
         orig_len, repl_len(1), pad_len
 
@@ -82,7 +82,7 @@
 .macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
     decl_orig(\oldinstr, as_max(repl_len(1), repl_len(2)) - orig_len)
 
-    .pushsection .altinstructions, "a", @progbits
+    .pushsection .altinstructions, "aw", @progbits
 
     altinstruction_entry .L\@_orig_s, .L\@_repl_s1, \feature1, \
         orig_len, repl_len(1), pad_len

xen/arch/x86/include/asm/alternative.h

@@ -90,7 +90,7 @@ extern void alternative_instructions(void);
 /* alternative assembly primitive: */
 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
         OLDINSTR_1(oldinstr, 1)                                         \
-        ".pushsection .altinstructions, \"a\", @progbits\n"             \
+        ".pushsection .altinstructions, \"aw\", @progbits\n"            \
         ALTINSTR_ENTRY(feature, 1)                                      \
         ".section .discard, \"a\", @progbits\n"                         \
         ".byte " alt_total_len "\n" /* total_len <= 255 */              \
@@ -101,7 +101,7 @@ extern void alternative_instructions(void);
 
 #define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
         OLDINSTR_2(oldinstr, 1, 2)                                      \
-        ".pushsection .altinstructions, \"a\", @progbits\n"             \
+        ".pushsection .altinstructions, \"aw\", @progbits\n"            \
         ALTINSTR_ENTRY(feature1, 1)                                     \
         ALTINSTR_ENTRY(feature2, 2)                                     \
         ".section .discard, \"a\", @progbits\n"                         \