/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 2014 Intel Corporation; author Matt Fleming
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*
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* Support for invoking 32-bit EFI runtime services from a 64-bit
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* kernel.
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*
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* The below thunking functions are only used after ExitBootServices()
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* has been called. This simplifies things considerably as compared with
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* the early EFI thunking because we can leave all the kernel state
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* intact (GDT, IDT, etc) and simply invoke the the 32-bit EFI runtime
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* services from __KERNEL32_CS. This means we can continue to service
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* interrupts across an EFI mixed mode call.
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*
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* We do however, need to handle the fact that we're running in a full
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* 64-bit virtual address space. Things like the stack and instruction
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* addresses need to be accessible by the 32-bit firmware, so we rely on
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* using the identity mappings in the EFI page table to access the stack
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* and kernel text (see efi_setup_page_tables()).
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*/
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#include <linux/linkage.h>
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#include <asm/page_types.h>
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#include <asm/segment.h>
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.text
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.code64
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ENTRY(efi64_thunk)
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push %rbp
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push %rbx
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/*
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* Switch to 1:1 mapped 32-bit stack pointer.
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*/
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movq %rsp, efi_saved_sp(%rip)
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movq efi_scratch(%rip), %rsp
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/*
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* Calculate the physical address of the kernel text.
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*/
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movq $__START_KERNEL_map, %rax
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subq phys_base(%rip), %rax
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/*
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* Push some physical addresses onto the stack. This is easier
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* to do now in a code64 section while the assembler can address
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* 64-bit values. Note that all the addresses on the stack are
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* 32-bit.
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*/
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subq $16, %rsp
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leaq efi_exit32(%rip), %rbx
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subq %rax, %rbx
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movl %ebx, 8(%rsp)
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leaq __efi64_thunk(%rip), %rbx
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subq %rax, %rbx
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call *%rbx
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movq efi_saved_sp(%rip), %rsp
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pop %rbx
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pop %rbp
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retq
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ENDPROC(efi64_thunk)
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/*
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* We run this function from the 1:1 mapping.
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*
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* This function must be invoked with a 1:1 mapped stack.
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*/
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ENTRY(__efi64_thunk)
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movl %ds, %eax
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push %rax
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movl %es, %eax
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push %rax
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movl %ss, %eax
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push %rax
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subq $32, %rsp
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movl %esi, 0x0(%rsp)
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movl %edx, 0x4(%rsp)
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movl %ecx, 0x8(%rsp)
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movq %r8, %rsi
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movl %esi, 0xc(%rsp)
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movq %r9, %rsi
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movl %esi, 0x10(%rsp)
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leaq 1f(%rip), %rbx
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movq %rbx, func_rt_ptr(%rip)
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/* Switch to 32-bit descriptor */
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pushq $__KERNEL32_CS
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leaq efi_enter32(%rip), %rax
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pushq %rax
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lretq
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1: addq $32, %rsp
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pop %rbx
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movl %ebx, %ss
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pop %rbx
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movl %ebx, %es
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pop %rbx
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movl %ebx, %ds
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/*
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* Convert 32-bit status code into 64-bit.
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*/
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test %rax, %rax
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jz 1f
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movl %eax, %ecx
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andl $0x0fffffff, %ecx
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andl $0xf0000000, %eax
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shl $32, %rax
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or %rcx, %rax
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1:
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ret
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ENDPROC(__efi64_thunk)
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ENTRY(efi_exit32)
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movq func_rt_ptr(%rip), %rax
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push %rax
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mov %rdi, %rax
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ret
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ENDPROC(efi_exit32)
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.code32
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/*
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* EFI service pointer must be in %edi.
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*
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* The stack should represent the 32-bit calling convention.
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*/
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ENTRY(efi_enter32)
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movl $__KERNEL_DS, %eax
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movl %eax, %ds
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movl %eax, %es
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movl %eax, %ss
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call *%edi
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/* We must preserve return value */
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movl %eax, %edi
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movl 72(%esp), %eax
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pushl $__KERNEL_CS
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pushl %eax
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lret
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ENDPROC(efi_enter32)
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.data
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.balign 8
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func_rt_ptr: .quad 0
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efi_saved_sp: .quad 0
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