[PATCH for-4.14] x86/cpu: fix build with clang 3.5

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Clang 3.5 complains with:

common.c:794:24: error: statement expression not allowed at file scope
                      i < ARRAY_SIZE(this_cpu(tss_page).ist_ssp); ++i )
                                     ^
/build/xen/include/asm/percpu.h:14:7: note: expanded from macro 'this_cpu'
    (*RELOC_HIDE(&per_cpu__##var, get_cpu_info()->per_cpu_offset))
      ^
/build/xen/include/xen/compiler.h:104:3: note: expanded from macro 'RELOC_HIDE'
  ({ unsigned long __ptr;                       \
  ^
/build/xen/include/xen/lib.h:68:69: note: expanded from macro 'ARRAY_SIZE'
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + __must_be_array(x))
                                                                    ^
/build/xen/include/xen/compiler.h:85:57: note: expanded from macro 
'__must_be_array'
  BUILD_BUG_ON_ZERO(__builtin_types_compatible_p(typeof(a), typeof(&a[0])))
                                                        ^
/build/xen/include/xen/lib.h:39:57: note: expanded from macro 
'BUILD_BUG_ON_ZERO'
#define BUILD_BUG_ON_ZERO(cond) sizeof(struct { int:-!!(cond); })
                                                        ^

Workaround this by defining the tss_page as a local variable. Adjust
other users of the per-cpu tss_page to also use the newly introduced
local variable.

No functional change expected.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/cpu/common.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 58f0876180..da74172776 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -738,9 +738,14 @@ void load_system_tables(void)
        unsigned int i, cpu = smp_processor_id();
        unsigned long stack_bottom = get_stack_bottom(),
                stack_top = stack_bottom & ~(STACK_SIZE - 1);
+       /*
+        * NB: define tss_page as a local variable because clang 3.5 doesn't
+        * support using ARRAY_SIZE against per-cpu variables.
+        */
+       struct tss_page *tss_page = &this_cpu(tss_page);
 
        /* The TSS may be live.  Disuade any clever optimisations. */
-       volatile struct tss64 *tss = &this_cpu(tss_page).tss;
+       volatile struct tss64 *tss = &tss_page->tss;
        seg_desc_t *gdt =
                this_cpu(gdt) - FIRST_RESERVED_GDT_ENTRY;
 
@@ -783,15 +788,14 @@ void load_system_tables(void)
         * volatile qualifier.
         */
        if (cpu_has_xen_shstk) {
-               volatile uint64_t *ist_ssp = this_cpu(tss_page).ist_ssp;
+               volatile uint64_t *ist_ssp = tss_page->ist_ssp;
 
                ist_ssp[0] = 0x8600111111111111ul;
                ist_ssp[IST_MCE] = stack_top + (IST_MCE * IST_SHSTK_SIZE) - 8;
                ist_ssp[IST_NMI] = stack_top + (IST_NMI * IST_SHSTK_SIZE) - 8;
                ist_ssp[IST_DB]  = stack_top + (IST_DB  * IST_SHSTK_SIZE) - 8;
                ist_ssp[IST_DF]  = stack_top + (IST_DF  * IST_SHSTK_SIZE) - 8;
-               for ( i = IST_DF + 1;
-                     i < ARRAY_SIZE(this_cpu(tss_page).ist_ssp); ++i )
+               for ( i = IST_DF + 1; i < ARRAY_SIZE(tss_page->ist_ssp); ++i )
                        ist_ssp[i] = 0x8600111111111111ul;
 
                wrmsrl(MSR_INTERRUPT_SSP_TABLE, (unsigned long)ist_ssp);
-- 
2.26.2