[RFC PATCH] efi: Add build error for new EFI arches that do not specify INITRD_MAX_ADDRESS_OFFSET

[Glenn Washburn <development@efficientek.com>]

Non-x86 EFI architectures were using a INITRD_MAX_ADDRESS_OFFSET defined
by the aarch64 architecture. This seems to generally work, as in no one
has complained about this. However, the code is misleading. Architectures
should explicitly set INITRD_MAX_ADDRESS_OFFSET. To avoid breaking current
EFI architectures, set to GRUB_EFI_MAX_USABLE_ADDRESS, effectively allowing
the entire address range. New architectures will fail to build until this
macro is set.

Signed-off-by: Glenn Washburn <development@efficientek.com>
---
My reading of a reply on the list[1] is that RISCV has no limit for the
initrd. But I think it would be good to point to documentation describing
limitations as in the ARM comments.

Glenn

[1] https://lists.gnu.org/archive/html/grub-devel/2021-07/msg00001.html
---
 grub-core/loader/efi/linux.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/grub-core/loader/efi/linux.c b/grub-core/loader/efi/linux.c
index ab8fb35adb05..8f5460ba11e0 100644
--- a/grub-core/loader/efi/linux.c
+++ b/grub-core/loader/efi/linux.c
@@ -28,6 +28,7 @@
 #include <grub/efi/efi.h>
 #include <grub/efi/fdtload.h>
 #include <grub/efi/memory.h>
+#include <grub/cpu/efi/memory.h>
 #include <grub/efi/pe32.h>
 #include <grub/efi/sb.h>
 #include <grub/i18n.h>
@@ -290,21 +291,30 @@ grub_linux_unload (void)
 }
 
 #if !defined(__i386__) && !defined(__x86_64__)
+#if defined (__arm__)
 /*
  * As per linux/Documentation/arm/Booting
  * ARM initrd needs to be covered by kernel linear mapping,
  * so place it in the first 512MB of DRAM.
- *
+ */
+#define INITRD_MAX_ADDRESS_OFFSET (512U * 1024 * 1024)
+#elif defined (__aarch64__)
+/*
  * As per linux/Documentation/arm64/booting.txt
  * ARM64 initrd needs to be contained entirely within a 1GB aligned window
  * of up to 32GB of size that covers the kernel image as well.
  * Since the EFI stub loader will attempt to load the kernel near start of
  * RAM, place the buffer in the first 32GB of RAM.
  */
-#ifdef __arm__
-#define INITRD_MAX_ADDRESS_OFFSET (512U * 1024 * 1024)
-#else /* __aarch64__ */
 #define INITRD_MAX_ADDRESS_OFFSET (32ULL * 1024 * 1024 * 1024)
+#elif defined (__ia64__) || defined (__riscv) || defined (__loongarch_lp64)
+/*
+ * There has been no investigation into constraints on the initrd address
+ * for these platforms. Allow all the available address space for now.
+ */
+#define INITRD_MAX_ADDRESS_OFFSET GRUB_EFI_MAX_USABLE_ADDRESS
+#else
+#error "Unknown INITRD_MAX_ADDRESS_OFFSET for architecture"
 #endif
 
 /*
-- 
2.34.1