Re: [PATCH v4] xen: Add Darwin.mk for GNU toolchains

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Roger,

> On 6 Feb 2026, at 18:25, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
> 
> On Fri, Feb 06, 2026 at 05:21:44PM +0100, 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=unknown, 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 toolchain from brew:
>> - brew install aarch64-elf-gcc aarch64-elf-binutils
>> - cd xen
>> - make XEN_TARGET_ARCH=arm64 CROSS_COMPILE=aarch64-elf- HOSTCC=clang
> 
> Instead of `cd xen` I would use `make xen ...`.

Ack the 'cd xen' line is useless and should be removed.

> 
>> 
>> Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> 
> Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> One comment below.
> 
>> ---
>> Changes since v3:
>> - set XEN_COMPILE_ARCH to unknown instead of Darwin
>> - list binutils as a dependency to install in brew in commit message
>> 
>> 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
>> ---
>> config/Darwin.mk | 7 +++++++
>> 1 file changed, 7 insertions(+)
>> create mode 100644 config/Darwin.mk
>> 
>> diff --git a/config/Darwin.mk b/config/Darwin.mk
>> new file mode 100644
>> index 000000000000..176b27eac676
>> --- /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.
> 
> Hm, is this actually fully true?  What's the Linux ABI exactly here?
> 
> FreeBSD builds Xen natively, and it's not using the Linux ABI.
> FreeBSD uses no specific -target to the compiler invocations, and the
> linker emulation is set to elf_x86_64_fbsd.
> 
> I think the point here is that the toolchain must support building ELF
> objects / images, because that's the binary format supported by Xen.
> Whether it's Linux ELF or FreeBSD ELF doesn't make a difference for
> standalone environments like the Xen kernel.

This file is also use while compiling the tools and for those you definitely
to cross compile as they depend on Linux ABI. Maybe that works on BSD
but i doubt this would be the case on mac os.

Maybe we could simplify the sentence to not say anything we are unsure:

# Cross compile on Mac OS

Tell me if that works for you and i can submit a v5 or this might be possible to
fix on commit.

Cheers
Bertrand

> 
> Thanks, Roger.