Re: [Xen-devel] [PATCH v3 3/7] x86: make PV hypercall entry points work with !CONFIG_PV

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Nov 08, 2018 at 08:39:36AM -0700, Jan Beulich wrote:
> >>> On 08.11.18 at 16:33, <wei.liu2@xxxxxxxxxx> wrote:
> > On Mon, Nov 05, 2018 at 09:11:44AM -0700, Jan Beulich wrote:
> >> >>> On 05.11.18 at 16:49, <andrew.cooper3@xxxxxxxxxx> wrote:
> >> > On 05/11/18 15:48, Wei Liu wrote:
> >> >> On Mon, Nov 05, 2018 at 08:04:37AM -0700, Jan Beulich wrote:
> >> >>>>>> On 02.11.18 at 16:55, <wei.liu2@xxxxxxxxxx> wrote:
> >> >>>> --- a/xen/arch/x86/x86_64/traps.c
> >> >>>> +++ b/xen/arch/x86/x86_64/traps.c
> >> >>>> @@ -298,8 +298,21 @@ static unsigned int write_stub_trampoline(
> >> >>>>  }
> >> >>>>  
> >> >>>>  DEFINE_PER_CPU(struct stubs, stubs);
> >> >>>> +
> >> >>>> +#ifdef CONFIG_PV
> >> >>>>  void lstar_enter(void);
> >> >>>>  void cstar_enter(void);
> >> >>>> +#else
> >> >>>> +static inline void lstar_enter(void)
> >> >>>> +{
> >> >>>> +    panic("%s called", __func__);
> >> >>>> +}
> >> >>>> +
> >> >>>> +static inline void cstar_enter(void)
> >> >>>> +{
> >> >>>> +    panic("%s called", __func__);
> >> >>>> +}
> >> >>>> +#endif /* CONFIG_PV */
> >> >>> Do we really need two separate stubs (and two separate string literals)
> >> >>> here?
> >> >> I think it is clearer if we have two distinct messages. But I'm not too
> >> >> fussed either way really. If you feel strongly about this, I'm happy to
> >> >> change it to only one function.
> >> > 
> >> > This is the correct way to do it.  __func__ will already be in the
> >> > string table, and the format string (being identical) will be merged.
> >> 
> >> Why would __func__ be in the string table already, for functions
> >> containing no other references to it?
> > 
> > What is the way forward? Do we really care if there is one more string
> > literal in the binary?
> 
> Well, if I understood what Andrew means, I could decide whether to
> give up my objection. Yes, a single string literal and a few insn bytes
> don't matter all that much. But nowadays everyone thinks this way
> everywhere, and one has to load dozens if not hundreds of megabytes
> of data just to get a basic OS booted.

Can we please do this sort of things systematically? Like, have a list
of criteria that state which when and where should we pay attention for
adding string literals. Arguing over this on a case by case basis is not
very productive.

BTW I don't think Xen is too bad in that regard -- it certainly doesn't
need hundreds of megabytes of data to boot.

Wei.

> 
> Jan
> 
> 

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