Re: [XEN PATCH][for-4.19 v4 2/8] x86: add deviations for variables only used in asm code

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.10.2023 09:58, Nicola Vetrini wrote:
> On 24/10/2023 09:32, Jan Beulich wrote:
>> On 23.10.2023 11:56, Nicola Vetrini wrote:
>>> --- a/xen/arch/x86/include/asm/asm_defns.h
>>> +++ b/xen/arch/x86/include/asm/asm_defns.h
>>> @@ -31,6 +31,7 @@ asm ( "\t.equ CONFIG_INDIRECT_THUNK, "
>>>   * gets set up by the containing function.
>>>   */
>>>  #ifdef CONFIG_FRAME_POINTER
>>> +/* SAF-1-safe */
>>>  register unsigned long current_stack_pointer asm("rsp");
>>>  # define ASM_CALL_CONSTRAINT , "+r" (current_stack_pointer)
>>>  #else
>>
>> SAF-1-safe is about symbols "used only by asm modules". This doesn't 
>> apply
>> to the declaration here.
>>
> 
> The wording could change to "asm code" if that is deemed clearer.

Question is what would be meant by "asm code"; "asm modules" is quite
clear.

>>> --- a/xen/arch/x86/setup.c
>>> +++ b/xen/arch/x86/setup.c
>>> @@ -75,6 +75,7 @@ static bool __initdata opt_invpcid = true;
>>>  boolean_param("invpcid", opt_invpcid);
>>>  bool __read_mostly use_invpcid;
>>>
>>> +/* SAF-1-safe Only used in asm code and within this source file */
>>>  unsigned long __read_mostly cr4_pv32_mask;
>>>
>>>  /* **** Linux config option: propagated to domain0. */
>>> @@ -147,12 +148,13 @@ cpumask_t __read_mostly cpu_present_map;
>>>  unsigned long __read_mostly xen_phys_start;
>>>
>>>  char __section(".init.bss.stack_aligned") __aligned(STACK_SIZE)
>>> -    cpu0_stack[STACK_SIZE];
>>> +    cpu0_stack[STACK_SIZE]; /* SAF-1-safe Only used in asm code and 
>>> below */
>>
>> Wasn't it that such comments need to live on the earlier line?
> 
> On the same line is fine as well. I personally found it less clear 
> putting that in the
> line above.

But please recall that these comments are intended to cover other
scanners as well. Iirc only Eclair accepts comments on the same line.
Nevertheless I realize that putting the comment on the earlier line
is problematic (and maybe also scanner dependent) when that ends up
in the middle of a declaration / definition.

Jan