EFI: constify a few table pointers

We shouldn't (and don't) modify any of these tables.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/common/efi/boot.c

@@ -75,7 +75,7 @@ static size_t wstrlen(const CHAR16 * s);
 static int set_color(u32 mask, int bpp, u8 *pos, u8 *sz);
 static bool_t match_guid(const EFI_GUID *guid1, const EFI_GUID *guid2);
 
-static EFI_BOOT_SERVICES *__initdata efi_bs;
+static const EFI_BOOT_SERVICES *__initdata efi_bs;
 static EFI_HANDLE __initdata efi_ih;
 
 static SIMPLE_TEXT_OUTPUT_INTERFACE *__initdata StdOut;

xen/common/efi/efi.h

@@ -18,12 +18,12 @@ struct efi_pci_rom {
 };
 
 extern unsigned int efi_num_ct;
-extern EFI_CONFIGURATION_TABLE *efi_ct;
+extern const EFI_CONFIGURATION_TABLE *efi_ct;
 
 extern unsigned int efi_version, efi_fw_revision;
 extern const CHAR16 *efi_fw_vendor;
 
-extern EFI_RUNTIME_SERVICES *efi_rs;
+extern const EFI_RUNTIME_SERVICES *efi_rs;
 
 extern UINTN efi_memmap_size, efi_mdesc_size;
 extern void *efi_memmap;

xen/common/efi/runtime.c

@@ -21,13 +21,13 @@ const bool_t efi_enabled = 1;
 #endif
 
 unsigned int __read_mostly efi_num_ct;
-EFI_CONFIGURATION_TABLE *__read_mostly efi_ct;
+const EFI_CONFIGURATION_TABLE *__read_mostly efi_ct;
 
 unsigned int __read_mostly efi_version;
 unsigned int __read_mostly efi_fw_revision;
 const CHAR16 *__read_mostly efi_fw_vendor;
 
-EFI_RUNTIME_SERVICES *__read_mostly efi_rs;
+const EFI_RUNTIME_SERVICES *__read_mostly efi_rs;
 #ifndef CONFIG_ARM /* TODO - disabled until implemented on ARM */
 static DEFINE_SPINLOCK(efi_rs_lock);
 #endif