Re: [PATCH 3/5] build: arm64: provide -target and -march if using clang

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 02/12/2024 07:52, Jan Beulich wrote:
> On 30.11.2024 18:15, Julien Grall wrote:
> > On 29/11/2024 22:12, Volodymyr Babchuk wrote:
> > > Jan Beulich <jbeulich@xxxxxxxx> writes:
> > > > On 29.11.2024 02:49, Volodymyr Babchuk wrote:
> > > > > --- a/config/arm64.mk
> > > > > +++ b/config/arm64.mk
> > > > > @@ -5,6 +5,10 @@ CONFIG_XEN_INSTALL_SUFFIX :=
> > > > >    
> > > > >    CFLAGS += #-marm -march= -mcpu= etc
> > > > >    
> > > > > +ifeq ($(clang),y)
> > > > > +CFLAGS += -target aarch64 -march=armv8-a
> > > > > +endif
> > > > Why is this dependent on (just?) $(clang), not (also?) $(llvm)?
> > > Because this parameter is handled by clang only. There is no harm in
> > > providing it explicitly. When building on arm64, value of this parameter
> > > will match the default value for the platform. When building on x86, we
> > > need to tell clang that it should generate arm64 code anyways. There is
> > > no reason in trying to make ARM build with x86 instruction set.
> > >
> > > > Also
> > > > this affects both toolstack builds and hypervisor. Is applying -march
> > > > like this actually appropriate for the toolstack?
> > > This is a good question. I can't see why this can't be appropriate for
> > > toolstack. I.e. what bad can happen when building the toolstack.
> > In the future, we may want to build the tools for Armv8-M. So I think
> > the -march should also applies for the toolstack.
> Perhaps I don't know enough of the Arm world, but: Wouldn't it be possible
> to build a tool stack suitable for a wide range for Arm64 flavors, while
> requiring more targeted hypervisor binaries?
Good question. There are some commonnality between ARMv8-M and ARMv8-R 
but I am not sure whether it means we could use -march=armv8-a build and 
run on ARMv8-M. Adding Ayan and Luca.
Cheers,

--
Julien Grall