[xen] Allow for platforms that have no Xen support

The Xen headers support only x86 and ARM.  Allow for platforms such as
LoongArch64 to build despite the absence of Xen support by providing
an architecture-specific <bits/xen.h> that simply does:

  #ifndef _BITS_XEN_H
  #define _BITS_XEN_H
  #include <ipxe/nonxen.h>
  #endif /* _BITS_XEN_H */

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/nonxen.h

@@ -0,0 +1,76 @@
+#ifndef _IPXE_NONXEN_H
+#define _IPXE_NONXEN_H
+
+/** @file
+ *
+ * Stub Xen definitions for platforms with no Xen support
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#define __XEN_GUEST_HANDLE(name)        __guest_handle_ ## name
+
+#define XEN_GUEST_HANDLE(name)          __XEN_GUEST_HANDLE(name)
+
+#define ___DEFINE_XEN_GUEST_HANDLE(name, type)	\
+	typedef type * __XEN_GUEST_HANDLE(name)
+
+#define __DEFINE_XEN_GUEST_HANDLE(name, type)			\
+	___DEFINE_XEN_GUEST_HANDLE(name, type);			\
+	___DEFINE_XEN_GUEST_HANDLE(const_##name, const type)
+
+#define DEFINE_XEN_GUEST_HANDLE(name)   __DEFINE_XEN_GUEST_HANDLE(name, name)
+
+typedef unsigned long xen_pfn_t;
+
+typedef unsigned long xen_ulong_t;
+
+struct arch_vcpu_info {};
+
+struct arch_shared_info {};
+
+#define XEN_LEGACY_MAX_VCPUS 0
+
+struct xen_hypervisor;
+
+static inline __attribute__ (( always_inline )) unsigned long
+xen_hypercall_1 ( struct xen_hypervisor *xen __unused,
+		  unsigned int hypercall __unused,
+		  unsigned long arg1 __unused ) {
+	return 1;
+}
+
+static inline __attribute__ (( always_inline )) unsigned long
+xen_hypercall_2 ( struct xen_hypervisor *xen __unused,
+		  unsigned int hypercall __unused,
+		  unsigned long arg1 __unused, unsigned long arg2 __unused ) {
+	return 1;
+}
+
+static inline __attribute__ (( always_inline )) unsigned long
+xen_hypercall_3 ( struct xen_hypervisor *xen __unused,
+		  unsigned int hypercall __unused,
+		  unsigned long arg1 __unused, unsigned long arg2 __unused,
+		  unsigned long arg3 __unused ) {
+	return 1;
+}
+
+static inline __attribute__ (( always_inline )) unsigned long
+xen_hypercall_4 ( struct xen_hypervisor *xen __unused,
+		  unsigned int hypercall __unused,
+		  unsigned long arg1 __unused, unsigned long arg2 __unused,
+		  unsigned long arg3 __unused, unsigned long arg4 __unused ) {
+	return 1;
+}
+
+static inline __attribute__ (( always_inline )) unsigned long
+xen_hypercall_5 ( struct xen_hypervisor *xen __unused,
+		  unsigned int hypercall __unused,
+		  unsigned long arg1 __unused, unsigned long arg2 __unused,
+		  unsigned long arg3 __unused, unsigned long arg4 __unused,
+		  unsigned long arg5 __unused ) {
+	return 1;
+}
+
+#endif /* _IPXE_NONXEN_H */

src/include/xen/import.pl

@@ -59,6 +59,10 @@ sub try_import_file {
     if ( /^\#include\s+[<\"](\S+)[>\"]/ ) {
       push @dependencies, catfile ( $subdir, $1 );
     }
+    # Patch "Unsupported architecture" line
+    if ( /^\#error\s+"Unsupported\sarchitecture"/ ) {
+      $_ = "#include <bits/xen.h>"
+    }
     # Write out line
     print $outfh "$_\n";
     # Apply FILE_LICENCE() immediately after include guard

src/include/xen/xen.h

@@ -19,7 +19,7 @@ FILE_LICENCE ( MIT );
 #elif defined(__arm__) || defined (__aarch64__)
 #include "arch-arm.h"
 #else
-#error "Unsupported architecture"
+#include <bits/xen.h>
 #endif
 
 #ifndef __ASSEMBLY__