x86/entry: Adjustments to "reduce assembly code size of entry points"

Some retroactive review, for if I'd got to the patch in time.

 * The new ASM-friendly BUILD_BUG_ON() should be in a header file.
 * entry_int82() wants the movl->movb treatment too.

Fixes: c144b9e324 ("x86: Reduce assembly code size of entry points")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

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

@@ -82,6 +82,14 @@ register unsigned long current_stack_pointer asm("rsp");
 
 #ifdef __ASSEMBLY__
 
+.macro BUILD_BUG_ON condstr cond:vararg
+        .if \cond
+        .error "Condition \"\condstr\" not satisfied"
+        .endif
+.endm
+/* preprocessor macro to make error message more user friendly */
+#define BUILD_BUG_ON(cond) BUILD_BUG_ON #cond cond
+
 #ifdef HAVE_AS_QUOTED_SYM
 #define SUBSECTION_LBL(tag)                        \
         .ifndef .L.tag;                            \

xen/arch/x86/x86_64/compat/entry.S

@@ -15,7 +15,7 @@ FUNC(entry_int82)
         ENDBR64
         ALTERNATIVE "", clac, X86_FEATURE_XEN_SMAP
         pushq $0
-        movl  $HYPERCALL_VECTOR, 4(%rsp)
+        movb  $HYPERCALL_VECTOR, 4(%rsp)
         SAVE_ALL compat=1 /* DPL1 gate, restricted to 32bit PV guests only. */
 
         SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */

xen/arch/x86/x86_64/entry.S

@@ -22,14 +22,6 @@
 #endif
 .endm
 
-.macro BUILD_BUG_ON condstr cond:vararg
-        .if \cond
-        .error "Condition \"\condstr\" not satisfied"
-        .endif
-.endm
-/* preprocessor macro to make error message more user friendly */
-#define BUILD_BUG_ON(cond) BUILD_BUG_ON #cond cond
-
 #ifdef CONFIG_PV
 /* %rbx: struct vcpu */
 FUNC_LOCAL(switch_to_kernel)