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

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Sent: 02 June 2020 10:06
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: paul@xxxxxxx; Roger Pau Monne <roger.pau@xxxxxxxxxx>; Jan Beulich 
> <jbeulich@xxxxxxxx>; Andrew
> Cooper <andrew.cooper3@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>
> Subject: [PATCH for-4.14] x86/cpu: fix build with clang 3.5
> 
> 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>

Release-acked-by: Paul Durrant <paul@xxxxxxx>

> ---
>  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