x86/efi: Build our own EFI services pointer table

It's not possible to dereference the EFI System table directly when
booting a 64-bit kernel on a 32-bit EFI firmware because the size of
pointers don't match.

In preparation for supporting the above use case, build a list of
function pointers on boot so that callers don't have to worry about
converting pointer sizes through multiple levels of indirection.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>

arch/x86/boot/compressed/head_32.S

@@ -42,26 +42,53 @@ ENTRY(startup_32)
 ENTRY(efi_pe_entry)
 	add	$0x4, %esp
 
+	call	1f
+1:	popl	%esi
+	subl	$1b, %esi
+
+	popl	%ecx
+	movl	%ecx, efi32_config(%esi)	/* Handle */
+	popl	%ecx
+	movl	%ecx, efi32_config+8(%esi)	/* EFI System table pointer */
+
+	/* Relocate efi_config->call() */
+	leal	efi32_config(%esi), %eax
+	add	%esi, 88(%eax)
+	pushl	%eax
+
 	call	make_boot_params
 	cmpl	$0, %eax
-	je	1f
-	movl	0x4(%esp), %esi
-	movl	(%esp), %ecx
+	je	fail
+	popl	%ecx
 	pushl	%eax
-	pushl	%esi
 	pushl	%ecx
-	sub	$0x4, %esp
+	jmp	2f		/* Skip efi_config initialization */
 
 ENTRY(efi_stub_entry)
 	add	$0x4, %esp
+	popl	%ecx
+	popl	%edx
+
+	call	1f
+1:	popl	%esi
+	subl	$1b, %esi
+
+	movl	%ecx, efi32_config(%esi)	/* Handle */
+	movl	%edx, efi32_config+8(%esi)	/* EFI System table pointer */
+
+	/* Relocate efi_config->call() */
+	leal	efi32_config(%esi), %eax
+	add	%esi, 88(%eax)
+	pushl	%eax
+2:
 	call	efi_main
 	cmpl	$0, %eax
 	movl	%eax, %esi
 	jne	2f
-1:
+fail:
 	/* EFI init failed, so hang. */
 	hlt
-	jmp	1b
+	jmp	fail
 2:
 	call	3f
 3:
@@ -202,6 +229,13 @@ relocated:
 	xorl	%ebx, %ebx
 	jmp	*%eax
 
+	.data
+efi32_config:
+	.fill 11,8,0
+	.long efi_call_phys
+	.long 0
+	.byte 0
+
 /*
  * Stack and heap for uncompression
  */