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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 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 <linux/objtool.h>
- #include <asm/page_types.h>
- #include <asm/segment.h>
- .text
- .code64
- SYM_FUNC_START(__efi64_thunk)
- STACK_FRAME_NON_STANDARD __efi64_thunk
- push %rbp
- push %rbx
- /*
- * Switch to 1:1 mapped 32-bit stack pointer.
- */
- movq %rsp, %rax
- movq efi_mixed_mode_stack_pa(%rip), %rsp
- push %rax
- /*
- * Copy args passed via the stack
- */
- subq $0x24, %rsp
- movq 0x18(%rax), %rbp
- movq 0x20(%rax), %rbx
- movq 0x28(%rax), %rax
- movl %ebp, 0x18(%rsp)
- movl %ebx, 0x1c(%rsp)
- movl %eax, 0x20(%rsp)
- /*
- * 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
- 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
- // This return instruction is not needed for correctness, as it will
- // never be reached. It only exists to make objtool happy, which will
- // otherwise complain about unreachable instructions in the callers.
- RET
- SYM_FUNC_END(__efi64_thunk)
- .section ".rodata", "a", @progbits
- .balign 16
- SYM_DATA_START(__efi64_thunk_ret_tramp)
- 1: movq 0x20(%rsp), %rsp
- pop %rbx
- pop %rbp
- ret
- int3
- .code32
- 2: pushl $__KERNEL_CS
- pushl %ebp
- lret
- SYM_DATA_END(__efi64_thunk_ret_tramp)
- .bss
- .balign 8
- SYM_DATA(efi_mixed_mode_stack_pa, .quad 0)
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