Re: [Buildroot] [PATCH v5 1/4] package/xen: fix build error when BR2_PACKAGE_XEN_TOOLS not enabled

[Stewart Hildebrand via buildroot <buildroot@buildroot.org>]

On 8/26/26 08:46, Neal Frager wrote:
> The 0002-Update-linker-flags.patch assumes that the qemu-xen files are included
> in the xen source tree. However, if BR2_PACKAGE_XEN_TOOLS is not enabled, the
> qemu-xen dependency will not be handled and the patch will fail to apply with
> the following error.
> 
> Fixes: build error below
> Applying 0002-Update-linker-flags.patch using patch:
> patching file tools/Makefile
> Hunk #1 succeeded at 36 (offset -1 lines).
> Hunk #2 succeeded at 185 (offset -8 lines).
> can't find file to patch at input line 76
> Perhaps you used the wrong -p or --strip option?
> The text leading up to this was:
> --------------------------
> |diff --git a/tools/qemu-xen/include/hw/xen/xen_native.h b/tools/qemu-xen/include/hw/xen/xen_native.h
> |index 6bcc83ba..2590904e 100644
> |--- a/tools/qemu-xen/include/hw/xen/xen_native.h
> |+++ b/tools/qemu-xen/include/hw/xen/xen_native.h
> --------------------------
> No file to patch.  Skipping patch.
> 1 out of 1 hunk ignored
> make: *** [package/pkg-generic.mk:239: output/build/xen-4.21.1/.stamp_patched] Error 1
> 
> To avoid making BR2_PACKAGE_XEN_TOOLS a required option, fix the
> 0002-Update-linker-flags.patch so that modifying source from the qemu-xen
> package is no longer included.
> 
> Instead of patching qemu-xen, a better solution is undefining the
> __XEN_INTERFACE_VERSION__ from the qemu-xen package.
> 
> To test:
> BR2_aarch64=y
> BR2_TOOLCHAIN_EXTERNAL=y
> BR2_TOOLCHAIN_EXTERNAL_BOOTLIN=y
> BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_AARCH64_GLIBC_STABLE=y
> BR2_PACKAGE_XEN=y
>  # BR2_PACKAGE_XEN_TOOLS is not set
> 
> Signed-off-by: Neal Frager <neal.frager@amd.com>

Reviewed-by: Stewart Hildebrand <stewart.hildebrand@amd.com>

Thank you for this. I just want to provide a few more details for future
reference.

__XEN_INTERFACE_VERSION__ being defined is a side-effect of including either
xen.git/xen/include/public/xen.h (via #include <xen/xen.h>) or
qemu.git/include/hw/xen/xen.h (via #include "hw/xen/xen.h"). In Qemu, we could
have considered changing the check in xen_native.h to
#if defined(__XEN_PUBLIC_XEN_H__) || defined(QEMU_HW_XEN_H)
Then we'd be checking for the header inclusion directly instead of relying on a
side-effect, and that would also allow passing -D__XEN_INTERFACE_VERSION__=...
as buildroot was doing. But this approach is not strictly necessary IMO, and it
would be better to find a solution without maintaining a patch for qemu.

For context, when building Xen tools, we define __XEN_INTERFACE_VERSION__ on the
command line via CFLAGS - see xen.git/tools/Rules.mk:
CFLAGS += -D__XEN_INTERFACE_VERSION__=__XEN_LATEST_INTERFACE_VERSION__

Xen tools has a build target for qemu
(xen.git/tools/Makefile:subdir-all-qemu-xen-dir), and it typically invokes the
qemu build with a fresh set of CFLAGS, i.e. the -D__XEN_INTERFACE_VERSION__=...
should be dropped. However, buildroot somehow propagates the
-D__XEN_INTERFACE_VERSION__=... when building qemu-xen, hence triggering the
include order assertion in qemu.git/include/hw/xen/xen_native.h.

So the fix herein is to undo the __XEN_INTERFACE_VERSION__ define on the command
line when building qemu. Thus, __XEN_INTERFACE_VERSION__ will be defined in the
usual manner when including the appropriate header.

> ---
> V1->V2:
> - changed method to modify patches instead of xen.mk
> V2->V3:
> - removed text from commit message which appears as start of patch
> V3->V4:
> - merged into patch series as the first patch
> V4->V5:
> - removed qemu-xen patch
> - undefined __XEN_INTERFACE_VERSION__ from qemu-xen
> ---
>  package/xen/0002-Update-linker-flags.patch | 16 +---------------
>  package/xen/xen.mk                         |  3 ++-
>  2 files changed, 3 insertions(+), 16 deletions(-)
> 
> diff --git a/package/xen/0002-Update-linker-flags.patch b/package/xen/0002-Update-linker-flags.patch
> index ac02722781..3ba678cd9b 100644
> --- a/package/xen/0002-Update-linker-flags.patch
> +++ b/package/xen/0002-Update-linker-flags.patch
> @@ -16,8 +16,7 @@ Upstream: Buildroot specific. This is a temporary patch for an intermediate bump
>  Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>
>  ---
>   tools/Makefile                              | 29 ++++++++++++++++++++-
> - tools/qemu-xen/include/hw/xen/xen_native.h |  2 +-
> - 2 files changed, 29 insertions(+), 2 deletions(-)
> + 1 file changed, 28 insertions(+), 1 deletions(-)
>  
>  diff --git a/tools/Makefile b/tools/Makefile
>  index a9a3196e..5d289651 100644
> @@ -69,19 +68,6 @@ index a9a3196e..5d289651 100644
>   		--bindir=$(LIBEXEC_BIN) \
>   		--datadir=$(SHAREDIR)/qemu-xen \
>   		--localstatedir=$(localstatedir) \
> -diff --git a/tools/qemu-xen/include/hw/xen/xen_native.h b/tools/qemu-xen/include/hw/xen/xen_native.h
> -index 6bcc83ba..2590904e 100644
> ---- a/tools/qemu-xen/include/hw/xen/xen_native.h
> -+++ b/tools/qemu-xen/include/hw/xen/xen_native.h
> -@@ -2,7 +2,7 @@
> - #define QEMU_HW_XEN_NATIVE_H
> - 
> - #ifdef __XEN_INTERFACE_VERSION__
> --#error In Xen native files, include xen_native.h before other Xen headers
> -+#warning In Xen native files, include xen_native.h before other Xen headers
> - #endif
> - 
> - /*
>  -- 
>  2.51.0
>  
> diff --git a/package/xen/xen.mk b/package/xen/xen.mk
> index 75252d1123..bddfdbba38 100644
> --- a/package/xen/xen.mk
> +++ b/package/xen/xen.mk
> @@ -40,7 +40,8 @@ XEN_MAKE_ENV = \
>  	CROSS_COMPILE=$(TARGET_CROSS) \
>  	HOST_EXTRACFLAGS="-Wno-error" \
>  	XEN_HAS_CHECKPOLICY=n \
> -	$(TARGET_CONFIGURE_OPTS)
> +	$(TARGET_CONFIGURE_OPTS) \
> +	EXTRA_CFLAGS_QEMU_XEN="-U__XEN_INTERFACE_VERSION__"
>  
>  ifeq ($(BR2_PACKAGE_XEN_HYPERVISOR),y)
>  XEN_MAKE_OPTS += dist-xen

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