[Xen-changelog] [xen stable-4.12] x86/tss: Fix clang build following c/s 7888440625

[patchbot@xxxxxxx]

commit 0a69b62aeec50add889d020dcd4eb69ed9cd6213
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Dec 6 12:37:18 2019 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Dec 6 12:37:18 2019 +0100

    x86/tss: Fix clang build following c/s 7888440625
    
    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>
    Reviewed-by: Wei Liu <wl@xxxxxxx>
    master commit: 1722da6c0c6f6b7b320bdd239c46c0cb1048f804
    master date: 2019-08-14 12:04:20 +0100
---
 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 e21cf0a310..0f5c549898 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -833,9 +833,11 @@ 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 *ptr = &per_cpu(tss_page, cpu);
 
-        rc = clone_mapping(&per_cpu(tss_page, cpu).tss, rpt);
+        BUILD_BUG_ON(sizeof(*ptr) != PAGE_SIZE);
+
+        rc = clone_mapping(&ptr->tss, rpt);
     }
     if ( !rc )
         rc = clone_mapping((void *)per_cpu(stubs.addr, cpu), rpt);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12

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