Re: [XEN PATCH 3/7] xen/x86: add missing instances of asmlinkage attributes

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

On 2023-11-30 17:44, Jan Beulich wrote:
> On 29.11.2023 16:24, Nicola Vetrini wrote:
>> --- a/xen/arch/x86/desc.c
>> +++ b/xen/arch/x86/desc.c
>> @@ -91,7 +91,7 @@ seg_desc_t boot_compat_gdt[PAGE_SIZE / 
>> sizeof(seg_desc_t)] =
>>   * References boot_cpu_gdt_table for a short period, until the CPUs 
>> switch
>>   * onto their per-CPU GDTs.
>>   */
>> -const struct desc_ptr boot_gdtr = {
>> +const struct desc_ptr asmlinkage boot_gdtr = {
>>      .limit = LAST_RESERVED_GDT_BYTE,
>>      .base = (unsigned long)(boot_gdt - FIRST_RESERVED_GDT_ENTRY),
>>  };
> 
> I'm not convinced asmlinkage is okay to use on data. Recall that in 
> principle
> it may expand to an attribute specifying a non-default calling 
> convention.
> Such attributes cannot be assumed to continue to be possible to apply 
> to
> non-functions, even if such may happen to work with a particular 
> compiler
> version.
> 

It's already being used on variables, I believe.

xen/arch/x86/mm.c:l1_pgentry_t asmlinkage __section(".bss.page_aligned") 
__aligned(PAGE_SIZE)
xen/arch/x86/setup.c:unsigned long asmlinkage __read_mostly 
cr4_pv32_mask;
xen/arch/x86/setup.c:char asmlinkage 
__section(".init.bss.stack_aligned") __aligned(STACK_SIZE)
xen/arch/x86/setup.c:unsigned int asmlinkage __initdata multiboot_ptr;

If you have concern about this particular variable, then we can fall 
back on SAF or just put a declaration in the appropriate place.

-- 
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)