Re: [XEN PATCH][for-4.19 v5 2/8] x86: add deviation for asm-only functions

[Jan Beulich <jbeulich@xxxxxxxx>]

On 31.10.2023 09:22, Nicola Vetrini wrote:
> On 2023-10-30 16:12, Jan Beulich wrote:
>> On 30.10.2023 10:11, Nicola Vetrini wrote:
>>> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
>>> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
>>> @@ -163,6 +163,15 @@ Therefore the absence of prior declarations is 
>>> safe."
>>>  -config=MC3R1.R8.4,reports+={safe, "first_area(any_loc(file(gcov)))"}
>>>  -doc_end
>>>
>>> +-doc_begin="Recognize the occurrence of current_stack_pointer as a 
>>> declaration."
>>> +-file_tag+={asm_defns, "^xen/arch/x86/include/asm/asm_defns\\.h$"}
>>> +-config=MC3R1.R8.4,declarations+={safe, 
>>> "loc(file(asm_defns))&&^current_stack_pointer$"}
>>> +-doc_end
>>> +
>>> +-doc_begin="asmlinkage is a marker to indicate that the function is 
>>> only used from asm modules."
>>> +-config=MC3R1.R8.4,declarations+={safe,"loc(text(^.*asmlinkage.*$, 
>>> -1..0))"}
>>> +-doc_end
>>
>> In the longer run asmlinkage will want using for functions used either 
>> way
>> between C and assembly (i.e. C->asm calls as well as asm->C ones). I'd 
>> like
>> to ask that the text please allow for that (e.g. s/from/to interface 
>> with/).
>>
>>> --- a/xen/arch/x86/hvm/svm/intr.c
>>> +++ b/xen/arch/x86/hvm/svm/intr.c
>>> @@ -123,7 +123,7 @@ static void svm_enable_intr_window(struct vcpu *v, 
>>> struct hvm_intack intack)
>>>          vmcb, general1_intercepts | GENERAL1_INTERCEPT_VINTR);
>>>  }
>>>
>>> -void svm_intr_assist(void)
>>> +asmlinkage void svm_intr_assist(void)
>>
>> Nit (here and below): Attributes, unless impossible for some specific
>> reason, should always go between type and identifier. Not all our code
>> is conforming to that, but I think a majority is, and hence you should
>> be able to find ample examples (taking e.g. __init).
>>
>>> --- a/xen/include/xen/compiler.h
>>> +++ b/xen/include/xen/compiler.h
>>> @@ -159,6 +159,9 @@
>>>  # define ASM_FLAG_OUT(yes, no) no
>>>  #endif
>>>
>>> +/* Mark a function or variable as used only from asm */
>>> +#define asmlinkage
>>
>> I appreciate this being an immediately "natural" place, but considering
>> what we know from Linux I think we ought to allow for arch overrides 
>> here
>> right away. For that I'm afraid compiler.h isn't best; it may still be
>> okay as long as at least an #ifndef is put around it. Imo, however, 
>> this
>> ought to go into xen/linkage.h, as is being introduced by "common:
>> assembly entry point type/size annotations". It's somewhat a shame that
>> this and the rest of that series has missed 4.18 ...
> 
> An #ifndef around what, exactly?

The #define. That way at least an arch's config.h can override it.

> Anyway, making (part of) this series 
> wait for approval
> until the other has been accepted into 4.19 (for which I have no 
> specific timeframe)
> does not seem that desirable to me.

It's not ideal, but you or anyone else are free to help that other work
make progress.

Jan