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-rw-r--r--arch/arm64/kernel/efi-rt-wrapper.S41
1 files changed, 41 insertions, 0 deletions
diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S
new file mode 100644
index 000000000000..05235ebb336d
--- /dev/null
+++ b/arch/arm64/kernel/efi-rt-wrapper.S
@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2018 Linaro Ltd <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/linkage.h>
+
+ENTRY(__efi_rt_asm_wrapper)
+ stp x29, x30, [sp, #-32]!
+ mov x29, sp
+
+ /*
+ * Register x18 is designated as the 'platform' register by the AAPCS,
+ * which means firmware running at the same exception level as the OS
+ * (such as UEFI) should never touch it.
+ */
+ stp x1, x18, [sp, #16]
+
+ /*
+ * We are lucky enough that no EFI runtime services take more than
+ * 5 arguments, so all are passed in registers rather than via the
+ * stack.
+ */
+ mov x8, x0
+ mov x0, x2
+ mov x1, x3
+ mov x2, x4
+ mov x3, x5
+ mov x4, x6
+ blr x8
+
+ ldp x1, x2, [sp, #16]
+ cmp x2, x18
+ ldp x29, x30, [sp], #32
+ b.ne 0f
+ ret
+0: b efi_handle_corrupted_x18 // tail call
+ENDPROC(__efi_rt_asm_wrapper)