Re: [PATCH v3] xen: Add Darwin.mk for GNU toolchains

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

> On 6 Feb 2026, at 14:29, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
> 
> On Fri, Feb 06, 2026 at 11:38:02AM +0100, Jan Beulich wrote:
>> On 06.02.2026 09:17, Bertrand Marquis wrote:
>>> Xen does not provide a Darwin build configuration for selecting
>>> GNU tool definitions. On macOS, the tools we use are either GNU
>>> compatible or we only rely on features supported by Mac OS, so
>>> using the GNU tool definitions is appropriate.
>>> 
>>> Add config/Darwin.mk to include StdGNU.mk and force
>>> XEN_COMPILE_ARCH=Darwin, ensuring Darwin builds always follow
>>> the cross-compile path as we depend on the Linux ABI so compiling
>>> on Mac OS is always a cross compilation case.
>>> 
>>> An example of how to build the hypervisor for arm64 on Mac OS
>>> (tools cannot be build for now) using a compiler from brew:
>>> - brew install aarch64-elf-gcc
>>> - cd xen
>>> - make XEN_TARGET_ARCH=arm64 CROSS_COMPILE=aarch64-elf- HOSTCC=gcc
>>> 
>>> Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
>>> ---
>>> Changes since v2:
>>> - Subject was "xen: Add macOS hypervisor build configuration"
>>> - Update Darwin.mk comments to more accurate versions (Jan)
>>> - Remove the build-on-macos help as we have no dependency on anything
>>>  coming from brew anymore and the toolchain can be retrieved by lots of
>>>  other solutions than brew on mac os. Switch to a simple doc in the
>>>  commit message instead
>> 
>> Did you see Roger's notice on Matrix about objcopy?
> 
> I think Bertrand considers objcopy to be part of the toolchain, hence
> "retrieving a toolchain" is meant to include objcopy (either the GNU,
> LLVM or elftoolchain one)

Sorry i only saw your message in matrix.

I checked and i installed both gcc and binutils in homebrew.

So i think the commit message needs modifying to stay:

brew install aarch64-elf-gcc aarch64-elf-binutils

to be fully complete.

> 
>>> --- /dev/null
>>> +++ b/config/Darwin.mk
>>> @@ -0,0 +1,7 @@
>>> +# Use GNU tool definitions as the tools we are using are either GNU 
>>> compatible
>>> +# or we only use features which are supported on Mac OS.
>>> +include $(XEN_ROOT)/config/StdGNU.mk
>>> +
>>> +# Xen uses Linux'es ABI so we are cross compiling on Mac OS.
>>> +# Force COMPILE_ARCH to a fake value to make sure it is always the case.
>>> +XEN_COMPILE_ARCH = Darwin
>> 
>> I first wondered why you say "fake", seeing the file is named Darwin.mk. But
>> in Config.mk's cross-compile check the build host OS doesn't even matter. So
>> yes, it needs faking here for the time being.
> 
> Hm, setting it to "Darwin" seems weird to me.  I understand the
> purpose of this is to force the user to set XEN_TARGET_ARCH
> explicitly.  I however wouldn't see it as fully uncorrect to not set
> this.  It will then execute `uname -m` and get `arm64` back for Apple
> silicon macs (which is kind of OK?).  Other I suggest we use a non-OSX
> specific value here, so that if required we could distinguish this
> case where the user is expected to provide XEN_COMPILE_ARCH.
> 
> Maybe XEN_COMPILE_ARCH = { unknown | undefined }?

I am ok to change this with either but maybe unsupported could be
a third choice?

Cheers
Bertrand

> 
> Thanks, Roger.