Re: [PATCH] xen: Use asm inline when available for alternatives

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

On 2025-04-22 22:02, Stefano Stabellini wrote:
> On Tue, 22 Apr 2025, Nicola Vetrini wrote:
>> On 2025-04-22 21:58, Stefano Stabellini wrote:
>> > On Tue, 22 Apr 2025, Andrew Cooper wrote:
>> > > On 22/04/2025 8:46 pm, Stefano Stabellini wrote:
>> > > > On Tue, 22 Apr 2025, Andrew Cooper wrote:
>> > > >> Compilers estimate the size of an asm() block for inlining purposes.
>> > > >>
>> > > >> Constructs such as ALTERNATIVE appear large due to the metadata,
>> > > depsite often
>> > > >> only being a handful of instructions.  asm inline() overrides the
>> > > estimation
>> > > >> to identify the block as being small.
>> > > >>
>> > > >> This has a substantial impact on inlining decisions, expected to be for
>> > > the
>> > > >> better given that the compiler has a more accurate picture to work
>> > > with.
>> > > >>
>> > > >> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> > > > Hi Andrew,
>> > > >
>> > > > If we are going to use asm_inline, please add a note to
>> > > > docs/misra/C-language-toolchain.rst where we keep record of all the
>> > > > language extensions we use.
>> > >
>> > > It's just asm(), and that's already discussed.
>> > >
>> > > I'm not sure what else you think is warranted.
>> >
>> >
>> > If it is just asm() then there is nothing to do. We only need to
>> > document extensions to the language, nothing else. Many of them are
>> > already documented under docs/misra/C-language-toolchain.rst (see for
>> > instance asm and __asm__).
>> >
>> > I see the critical part of the patch for this question is:
>> >
>> > > +#if CONFIG_CC_HAS_ASM_INLINE
>> > > +# define asm_inline asm __inline
>> > > +#else
>> > > +# define asm_inline asm
>> > > +#endif
>> >
>> > it looks like __inline is an extension ?
>> 
>> I see. It was added to the tool configuration, but not there in the 
>> rst
>> (__inline__ as well), hence why there are no CI failures.
> 
> I see __inline__|__inline in toolchain.ecl. Nicola, would you be up for
> sending a small patch to docs/misra/C-language-toolchain.rst to add 
> them?

Yes, no problem. I'll take the occasion to see whether there are other 
gaps. Perhaps there's a clever way to ensure these files do not go out 
of sync?

-- 
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253