10570 Need workaround to EFI boot on AMI BIOS

*** 20,35 ****
--- 20,37 ----
   */
  /*
   * Copyright (c) 2002, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright 2012 Nexenta Systems, Inc.  All rights reserved.
   * Copyright 2014 Toomas Soome <tsoome@me.com>
+  * Copyright (c) 2019, Joyent, Inc.
   */
  
  #ifndef _SYS_EFI_PARTITION_H
  #define _SYS_EFI_PARTITION_H
  
  #include <sys/uuid.h>
+ #include <sys/stddef.h>
  
  #ifdef  __cplusplus
  extern "C" {
  #endif
  
*** 44,53 ****
--- 46,65 ----
                              (8 * sizeof (char)) + \
                              (1 * (sizeof (struct uuid)))))
  
  #define EFI_SIGNATURE   0x5452415020494645ULL
  
+ /*
+  * Although the EFI spec is clear that sizeof (efi_gpt_t) is a valid value
+  * (512), at least one EFI system (AMI v4.6.4.1) incorrectly expects this to be
+  * exactly the size of the structure defined in the spec, that is, 92.
+  *
+  * As the reserved section is never used, the modified value works fine
+  * everywhere else.
+  */
+ #define EFI_HEADER_SIZE (offsetof(efi_gpt_t, efi_gpt_Reserved2))
+ 
  /* EFI Guid Partition Table Header -- little endian on-disk format */
  typedef struct efi_gpt {
          uint64_t        efi_gpt_Signature;
          uint_t          efi_gpt_Revision;
          uint_t          efi_gpt_HeaderSize;