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

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

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 ...
>
> Jan
An #ifndef around what, exactly? 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.

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