Re: [PATCH v7 03/19] xen/riscv: introduce extenstion support check by compiler

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

On Thu, 2024-04-04 at 17:43 +0200, Jan Beulich wrote:
> On 04.04.2024 17:18, Oleksii wrote:
> > On Thu, 2024-04-04 at 12:07 +0200, Jan Beulich wrote:
> > > On 03.04.2024 12:19, Oleksii Kurochko wrote:
> > > > --- a/xen/arch/riscv/arch.mk
> > > > +++ b/xen/arch/riscv/arch.mk
> > > > @@ -3,16 +3,27 @@
> > > >  
> > > >  $(call cc-options-add,CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS))
> > > >  
> > > > -CFLAGS-$(CONFIG_RISCV_64) += -mabi=lp64
> > > > +riscv-abi-$(CONFIG_RISCV_32) := -mabi=ilp32
> > > > +riscv-abi-$(CONFIG_RISCV_64) := -mabi=lp64
> > > >  
> > > >  riscv-march-$(CONFIG_RISCV_ISA_RV64G) := rv64g
> > > >  riscv-march-$(CONFIG_RISCV_ISA_C)       := $(riscv-march-y)c
> > > >  
> > > > +riscv-generic-flags := $(riscv-abi-y) -march=$(riscv-march-y)
> > > > +
> > > > +zbb := $(call as-insn,$(CC) $(riscv-generic-
> > > > flags)_zbb,"",_zbb)
> > > 
> > > While committing another question popped up: Why "" (i.e. no
> > > insn)
> > > here, ...
> > > 
> > > > +zihintpause := $(call as-insn,\
> > > > +               $(CC) $(riscv-generic-
> > > > flags)_zihintpause,"pause",_zihintpause)
> > > 
> > > ... but "pause" here?
> > 
> > In the case of the Zbb extension, we don't check for a specific
> > instruction, but with the Zihintpause, the idea was to verify if
> > the
> > pause instruction is supported or not.
> 
> And why's this verification relevant here, but not for Zbb?
It is not relevant and can be dropped. I'll do a follow-up patch.

~ Oleksii

> 
> Jan
> 
> > However, in both checks, there
> > might be no instruction as an argument of as-insn.
> > 
> > ~ Oleksii
>