[Xen-devel] [PATCH] x86/tss: Fix clang build following c/s 7888440625

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Clang-3.5 from Debian Jessie fails with:

  smpboot.c:829:29: error: statement expression not allowed at file scope
          BUILD_BUG_ON(sizeof(this_cpu(tss_page)) != PAGE_SIZE);
                              ^
  /local/xen.git/xen/include/asm/percpu.h:14:7: note: expanded from macro
          'this_cpu'
      (*RELOC_HIDE(&per_cpu__##var, get_cpu_info()->per_cpu_offset))
        ^
  /local/xen.git/xen/include/xen/compiler.h:98:3: note: expanded from macro
          'RELOC_HIDE'
    ({ unsigned long __ptr;                       \
    ^
  /local/xen.git/xen/include/xen/lib.h:26:53: note: expanded from macro
          'BUILD_BUG_ON'
  #define BUILD_BUG_ON(cond) ((void)BUILD_BUG_ON_ZERO(cond))
                                                      ^
  /local/xen.git/xen/include/xen/lib.h:25:57: note: expanded from macro
          'BUILD_BUG_ON_ZERO'
  #define BUILD_BUG_ON_ZERO(cond) sizeof(struct { int:-!!(cond); })
                                                          ^
  1 error generated.
  /local/xen.git/xen/Rules.mk:202: recipe for target 'smpboot.o' failed

This is obviously a compiler bug because the BUILD_BUG_ON() is not at file
scope.  However, it can be worked around by using a local variable.

Spotted by Gitlab CI.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/smpboot.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 5057109a77..85c81c247e 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -826,9 +826,11 @@ static int setup_cpu_root_pgt(unsigned int cpu)
         rc = clone_mapping(idt_tables[cpu], rpt);
     if ( !rc )
     {
-        BUILD_BUG_ON(sizeof(this_cpu(tss_page)) != PAGE_SIZE);
+        struct tss_page *this_tss = &per_cpu(tss_page, cpu);
 
-        rc = clone_mapping(&per_cpu(tss_page, cpu).tss, rpt);
+        BUILD_BUG_ON(sizeof(*this_tss) != PAGE_SIZE);
+
+        rc = clone_mapping(&this_tss->tss, rpt);
     }
     if ( !rc )
         rc = clone_mapping((void *)per_cpu(stubs.addr, cpu), rpt);
-- 
2.11.0


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