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/* SPDX-License-Identifier: GPL-2.0 */ /* * Copyright (C) 2014 Intel Corporation; author Matt Fleming * * Support for invoking 32-bit EFI runtime services from a 64-bit * kernel. * * The below thunking functions are only used after ExitBootServices() * has been called. This simplifies things considerably as compared with * the early EFI thunking because we can leave all the kernel state * intact (GDT, IDT, etc) and simply invoke the the 32-bit EFI runtime * services from __KERNEL32_CS. This means we can continue to service * interrupts across an EFI mixed mode call. * * We do however, need to handle the fact that we're running in a full * 64-bit virtual address space. Things like the stack and instruction * addresses need to be accessible by the 32-bit firmware, so we rely on * using the identity mappings in the EFI page table to access the stack * and kernel text (see efi_setup_page_tables()). */ #include <linux/linkage.h> #include <asm/page_types.h> #include <asm/segment.h> .text .code64 SYM_CODE_START(__efi64_thunk) push %rbp push %rbx /* * Switch to 1:1 mapped 32-bit stack pointer. */ movq %rsp, %rax movq efi_scratch(%rip), %rsp push %rax /* * Calculate the physical address of the kernel text. */ movq $__START_KERNEL_map, %rax subq phys_base(%rip), %rax leaq 1f(%rip), %rbp leaq 2f(%rip), %rbx subq %rax, %rbp subq %rax, %rbx subq $28, %rsp movl %ebx, 0x0(%rsp) /* return address */ movl %esi, 0x4(%rsp) movl %edx, 0x8(%rsp) movl %ecx, 0xc(%rsp) movl %r8d, 0x10(%rsp) movl %r9d, 0x14(%rsp) /* Switch to 32-bit descriptor */ pushq $__KERNEL32_CS pushq %rdi /* EFI runtime service address */ lretq 1: movq 24(%rsp), %rsp pop %rbx pop %rbp retq .code32 2: pushl $__KERNEL_CS pushl %ebp lret SYM_CODE_END(__efi64_thunk) |