arch/x86/boot/compressed/head_64.S - third_party/linux - Git at Google

 /* SPDX-License-Identifier: GPL-2.0 */
 /*
  *  linux/boot/head.S
  *
  *  Copyright (C) 1991, 1992, 1993  Linus Torvalds
  */

 /*
  *  head.S contains the 32-bit startup code.
  *
  * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
  * the page directory will exist. The startup code will be overwritten by
  * the page directory. [According to comments etc elsewhere on a compressed
  * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
  *
  * Page 0 is deliberately kept safe, since System Management Mode code in
  * laptops may need to access the BIOS data stored there.  This is also
  * useful for future device drivers that either access the BIOS via VM86
  * mode.
  */

 /*
  * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
  */
 	.code32
 	.text

 #include <linux/init.h>
 #include <linux/linkage.h>
 #include <asm/segment.h>
 #include <asm/boot.h>
 #include <asm/msr.h>
 #include <asm/processor-flags.h>
 #include <asm/asm-offsets.h>
 #include <asm/bootparam.h>
 #include "pgtable.h"

 /*
  * Locally defined symbols should be marked hidden:
  */
 	.hidden _bss
 	.hidden _ebss
 	.hidden _got
 	.hidden _egot

 	__HEAD
 	.code32
 ENTRY(startup_32)
 	/*
 	 * 32bit entry is 0 and it is ABI so immutable!
 	 * If we come here directly from a bootloader,
 	 * kernel(text+data+bss+brk) ramdisk, zero_page, command line
 	 * all need to be under the 4G limit.
 	 */
 	cld
 	/*
 	 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
 	 * us to not reload segments
 	 */
 	testb $KEEP_SEGMENTS, BP_loadflags(%esi)
 	jnz 1f

 	cli
 	movl	$(__BOOT_DS), %eax
 	movl	%eax, %ds
 	movl	%eax, %es
 	movl	%eax, %ss
 1:

 /*
  * Calculate the delta between where we were compiled to run
  * at and where we were actually loaded at.  This can only be done
  * with a short local call on x86.  Nothing  else will tell us what
  * address we are running at.  The reserved chunk of the real-mode
  * data at 0x1e4 (defined as a scratch field) are used as the stack
  * for this calculation. Only 4 bytes are needed.
  */
 	leal	(BP_scratch+4)(%esi), %esp
 	call	1f
 1:	popl	%ebp
 	subl	$1b, %ebp

 /* setup a stack and make sure cpu supports long mode. */
 	movl	$boot_stack_end, %eax
 	addl	%ebp, %eax
 	movl	%eax, %esp

 	call	verify_cpu
 	testl	%eax, %eax
 	jnz	no_longmode

 /*
  * Compute the delta between where we were compiled to run at
  * and where the code will actually run at.
  *
  * %ebp contains the address we are loaded at by the boot loader and %ebx
  * contains the address where we should move the kernel image temporarily
  * for safe in-place decompression.
  */

 #ifdef CONFIG_RELOCATABLE
 	movl	%ebp, %ebx
 	movl	BP_kernel_alignment(%esi), %eax
 	decl	%eax
 	addl	%eax, %ebx
 	notl	%eax
 	andl	%eax, %ebx
 	cmpl	$LOAD_PHYSICAL_ADDR, %ebx
 	jge	1f
 #endif
 	movl	$LOAD_PHYSICAL_ADDR, %ebx
 1:

 	/* Target address to relocate to for decompression */
 	movl	BP_init_size(%esi), %eax
 	subl	$_end, %eax
 	addl	%eax, %ebx

 /*
  * Prepare for entering 64 bit mode
  */

 	/* Load new GDT with the 64bit segments using 32bit descriptor */
 	addl	%ebp, gdt+2(%ebp)
 	lgdt	gdt(%ebp)

 	/* Enable PAE mode */
 	movl	%cr4, %eax
 	orl	$X86_CR4_PAE, %eax
 	movl	%eax, %cr4

  /*
   * Build early 4G boot pagetable
   */
 	/*
 	 * If SEV is active then set the encryption mask in the page tables.
 	 * This will insure that when the kernel is copied and decompressed
 	 * it will be done so encrypted.
 	 */
 	call	get_sev_encryption_bit
 	xorl	%edx, %edx
 	testl	%eax, %eax
 	jz	1f
 	subl	$32, %eax	/* Encryption bit is always above bit 31 */
 	bts	%eax, %edx	/* Set encryption mask for page tables */
 1:

 	/* Initialize Page tables to 0 */
 	leal	pgtable(%ebx), %edi
 	xorl	%eax, %eax
 	movl	$(BOOT_INIT_PGT_SIZE/4), %ecx
 	rep	stosl

 	/* Build Level 4 */
 	leal	pgtable + 0(%ebx), %edi
 	leal	0x1007 (%edi), %eax
 	movl	%eax, 0(%edi)
 	addl	%edx, 4(%edi)

 	/* Build Level 3 */
 	leal	pgtable + 0x1000(%ebx), %edi
 	leal	0x1007(%edi), %eax
 	movl	$4, %ecx
 1:	movl	%eax, 0x00(%edi)
 	addl	%edx, 0x04(%edi)
 	addl	$0x00001000, %eax
 	addl	$8, %edi
 	decl	%ecx
 	jnz	1b

 	/* Build Level 2 */
 	leal	pgtable + 0x2000(%ebx), %edi
 	movl	$0x00000183, %eax
 	movl	$2048, %ecx
 1:	movl	%eax, 0(%edi)
 	addl	%edx, 4(%edi)
 	addl	$0x00200000, %eax
 	addl	$8, %edi
 	decl	%ecx
 	jnz	1b

 	/* Enable the boot page tables */
 	leal	pgtable(%ebx), %eax
 	movl	%eax, %cr3

 	/* Enable Long mode in EFER (Extended Feature Enable Register) */
 	movl	$MSR_EFER, %ecx
 	rdmsr
 	btsl	$_EFER_LME, %eax
 	wrmsr

 	/* After gdt is loaded */
 	xorl	%eax, %eax
 	lldt	%ax
 	movl    $__BOOT_TSS, %eax
 	ltr	%ax

 	/*
 	 * Setup for the jump to 64bit mode
 	 *
 	 * When the jump is performend we will be in long mode but
 	 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1
 	 * (and in turn EFER.LMA = 1).	To jump into 64bit mode we use
 	 * the new gdt/idt that has __KERNEL_CS with CS.L = 1.
 	 * We place all of the values on our mini stack so lret can
 	 * used to perform that far jump.
 	 */
 	pushl	$__KERNEL_CS
 	leal	startup_64(%ebp), %eax
 #ifdef CONFIG_EFI_MIXED
 	movl	efi32_config(%ebp), %ebx
 	cmp	$0, %ebx
 	jz	1f
 	leal	handover_entry(%ebp), %eax
 1:
 #endif
 	pushl	%eax

 	/* Enter paged protected Mode, activating Long Mode */
 	movl	$(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */
 	movl	%eax, %cr0

 	/* Jump from 32bit compatibility mode into 64bit mode. */
 	lret
 ENDPROC(startup_32)

 #ifdef CONFIG_EFI_MIXED
 	.org 0x190
 ENTRY(efi32_stub_entry)
 	add	$0x4, %esp		/* Discard return address */
 	popl	%ecx
 	popl	%edx
 	popl	%esi

 	leal	(BP_scratch+4)(%esi), %esp
 	call	1f
 1:	pop	%ebp
 	subl	$1b, %ebp

 	movl	%ecx, efi32_config(%ebp)
 	movl	%edx, efi32_config+8(%ebp)
 	sgdtl	efi32_boot_gdt(%ebp)

 	leal	efi32_config(%ebp), %eax
 	movl	%eax, efi_config(%ebp)

 	jmp	startup_32
 ENDPROC(efi32_stub_entry)
 #endif

 	.code64
 	.org 0x200
 ENTRY(startup_64)
 	/*
 	 * 64bit entry is 0x200 and it is ABI so immutable!
 	 * We come here either from startup_32 or directly from a
 	 * 64bit bootloader.
 	 * If we come here from a bootloader, kernel(text+data+bss+brk),
 	 * ramdisk, zero_page, command line could be above 4G.
 	 * We depend on an identity mapped page table being provided
 	 * that maps our entire kernel(text+data+bss+brk), zero page
 	 * and command line.
 	 */

 	/* Setup data segments. */
 	xorl	%eax, %eax
 	movl	%eax, %ds
 	movl	%eax, %es
 	movl	%eax, %ss
 	movl	%eax, %fs
 	movl	%eax, %gs

 	/*
 	 * Compute the decompressed kernel start address.  It is where
 	 * we were loaded at aligned to a 2M boundary. %rbp contains the
 	 * decompressed kernel start address.
 	 *
 	 * If it is a relocatable kernel then decompress and run the kernel
 	 * from load address aligned to 2MB addr, otherwise decompress and
 	 * run the kernel from LOAD_PHYSICAL_ADDR
 	 *
 	 * We cannot rely on the calculation done in 32-bit mode, since we
 	 * may have been invoked via the 64-bit entry point.
 	 */

 	/* Start with the delta to where the kernel will run at. */
 #ifdef CONFIG_RELOCATABLE
 	leaq	startup_32(%rip) /* - $startup_32 */, %rbp
 	movl	BP_kernel_alignment(%rsi), %eax
 	decl	%eax
 	addq	%rax, %rbp
 	notq	%rax
 	andq	%rax, %rbp
 	cmpq	$LOAD_PHYSICAL_ADDR, %rbp
 	jge	1f
 #endif
 	movq	$LOAD_PHYSICAL_ADDR, %rbp
 1:

 	/* Target address to relocate to for decompression */
 	movl	BP_init_size(%rsi), %ebx
 	subl	$_end, %ebx
 	addq	%rbp, %rbx

 	/* Set up the stack */
 	leaq	boot_stack_end(%rbx), %rsp

 	/*
 	 * paging_prepare() and cleanup_trampoline() below can have GOT
 	 * references. Adjust the table with address we are running at.
 	 *
 	 * Zero RAX for adjust_got: the GOT was not adjusted before;
 	 * there's no adjustment to undo.
 	 */
 	xorq	%rax, %rax

 	/*
 	 * Calculate the address the binary is loaded at and use it as
 	 * a GOT adjustment.
 	 */
 	call	1f
 1:	popq	%rdi
 	subq	$1b, %rdi

 	call	adjust_got

 	/*
 	 * At this point we are in long mode with 4-level paging enabled,
 	 * but we might want to enable 5-level paging or vice versa.
 	 *
 	 * The problem is that we cannot do it directly. Setting or clearing
 	 * CR4.LA57 in long mode would trigger #GP. So we need to switch off
 	 * long mode and paging first.
 	 *
 	 * We also need a trampoline in lower memory to switch over from
 	 * 4- to 5-level paging for cases when the bootloader puts the kernel
 	 * above 4G, but didn't enable 5-level paging for us.
 	 *
 	 * The same trampoline can be used to switch from 5- to 4-level paging
 	 * mode, like when starting 4-level paging kernel via kexec() when
 	 * original kernel worked in 5-level paging mode.
 	 *
 	 * For the trampoline, we need the top page table to reside in lower
 	 * memory as we don't have a way to load 64-bit values into CR3 in
 	 * 32-bit mode.
 	 *
 	 * We go though the trampoline even if we don't have to: if we're
 	 * already in a desired paging mode. This way the trampoline code gets
 	 * tested on every boot.
 	 */

 	/* Make sure we have GDT with 32-bit code segment */
 	leaq	gdt(%rip), %rax
 	movq	%rax, gdt64+2(%rip)
 	lgdt	gdt64(%rip)

 	/*
 	 * paging_prepare() sets up the trampoline and checks if we need to
 	 * enable 5-level paging.
 	 *
 	 * Address of the trampoline is returned in RAX.
 	 * Non zero RDX on return means we need to enable 5-level paging.
 	 *
 	 * RSI holds real mode data and needs to be preserved across
 	 * this function call.
 	 */
 	pushq	%rsi
 	movq	%rsi, %rdi		/* real mode address */
 	call	paging_prepare
 	popq	%rsi

 	/* Save the trampoline address in RCX */
 	movq	%rax, %rcx

 	/*
 	 * Load the address of trampoline_return() into RDI.
 	 * It will be used by the trampoline to return to the main code.
 	 */
 	leaq	trampoline_return(%rip), %rdi

 	/* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */
 	pushq	$__KERNEL32_CS
 	leaq	TRAMPOLINE_32BIT_CODE_OFFSET(%rax), %rax
 	pushq	%rax
 	lretq
 trampoline_return:
 	/* Restore the stack, the 32-bit trampoline uses its own stack */
 	leaq	boot_stack_end(%rbx), %rsp

 	/*
 	 * cleanup_trampoline() would restore trampoline memory.
 	 *
 	 * RDI is address of the page table to use instead of page table
 	 * in trampoline memory (if required).
 	 *
 	 * RSI holds real mode data and needs to be preserved across
 	 * this function call.
 	 */
 	pushq	%rsi
 	leaq	top_pgtable(%rbx), %rdi
 	call	cleanup_trampoline
 	popq	%rsi

 	/* Zero EFLAGS */
 	pushq	$0
 	popfq

 	/*
 	 * Previously we've adjusted the GOT with address the binary was
 	 * loaded at. Now we need to re-adjust for relocation address.
 	 *
 	 * Calculate the address the binary is loaded at, so that we can
 	 * undo the previous GOT adjustment.
 	 */
 	call	1f
 1:	popq	%rax
 	subq	$1b, %rax

 	/* The new adjustment is the relocation address */
 	movq	%rbx, %rdi
 	call	adjust_got

 /*
  * Copy the compressed kernel to the end of our buffer
  * where decompression in place becomes safe.
  */
 	pushq	%rsi
 	leaq	(_bss-8)(%rip), %rsi
 	leaq	(_bss-8)(%rbx), %rdi
 	movq	$_bss /* - $startup_32 */, %rcx
 	shrq	$3, %rcx
 	std
 	rep	movsq
 	cld
 	popq	%rsi

 /*
  * Jump to the relocated address.
  */
 	leaq	relocated(%rbx), %rax
 	jmp	*%rax

 #ifdef CONFIG_EFI_STUB

 /* The entry point for the PE/COFF executable is efi_pe_entry. */
 ENTRY(efi_pe_entry)
 	movq	%rcx, efi64_config(%rip)	/* Handle */
 	movq	%rdx, efi64_config+8(%rip) /* EFI System table pointer */

 	leaq	efi64_config(%rip), %rax
 	movq	%rax, efi_config(%rip)

 	call	1f
 1:	popq	%rbp
 	subq	$1b, %rbp

 	/*
 	 * Relocate efi_config->call().
 	 */
 	addq	%rbp, efi64_config+40(%rip)

 	movq	%rax, %rdi
 	call	make_boot_params
 	cmpq	$0,%rax
 	je	fail
 	mov	%rax, %rsi
 	leaq	startup_32(%rip), %rax
 	movl	%eax, BP_code32_start(%rsi)
 	jmp	2f		/* Skip the relocation */

 handover_entry:
 	call	1f
 1:	popq	%rbp
 	subq	$1b, %rbp

 	/*
 	 * Relocate efi_config->call().
 	 */
 	movq	efi_config(%rip), %rax
 	addq	%rbp, 40(%rax)
 2:
 	movq	efi_config(%rip), %rdi
 	call	efi_main
 	movq	%rax,%rsi
 	cmpq	$0,%rax
 	jne	2f
 fail:
 	/* EFI init failed, so hang. */
 	hlt
 	jmp	fail
 2:
 	movl	BP_code32_start(%esi), %eax
 	leaq	startup_64(%rax), %rax
 	jmp	*%rax
 ENDPROC(efi_pe_entry)

 	.org 0x390
 ENTRY(efi64_stub_entry)
 	movq	%rdi, efi64_config(%rip)	/* Handle */
 	movq	%rsi, efi64_config+8(%rip) /* EFI System table pointer */

 	leaq	efi64_config(%rip), %rax
 	movq	%rax, efi_config(%rip)

 	movq	%rdx, %rsi
 	jmp	handover_entry
 ENDPROC(efi64_stub_entry)
 #endif

 	.text
 relocated:

 /*
  * Clear BSS (stack is currently empty)
  */
 	xorl	%eax, %eax
 	leaq    _bss(%rip), %rdi
 	leaq    _ebss(%rip), %rcx
 	subq	%rdi, %rcx
 	shrq	$3, %rcx
 	rep	stosq

 /*
  * Do the extraction, and jump to the new kernel..
  */
 	pushq	%rsi			/* Save the real mode argument */
 	movq	%rsi, %rdi		/* real mode address */
 	leaq	boot_heap(%rip), %rsi	/* malloc area for uncompression */
 	leaq	input_data(%rip), %rdx  /* input_data */
 	movl	$z_input_len, %ecx	/* input_len */
 	movq	%rbp, %r8		/* output target address */
 	movq	$z_output_len, %r9	/* decompressed length, end of relocs */
 	call	extract_kernel		/* returns kernel location in %rax */
 	popq	%rsi

 /*
  * Jump to the decompressed kernel.
  */
 	jmp	*%rax

 /*
  * Adjust the global offset table
  *
  * RAX is the previous adjustment of the table to undo (use 0 if it's the
  * first time we touch GOT).
  * RDI is the new adjustment to apply.
  */
 adjust_got:
 	/* Walk through the GOT adding the address to the entries */
 	leaq	_got(%rip), %rdx
 	leaq	_egot(%rip), %rcx
 1:
 	cmpq	%rcx, %rdx
 	jae	2f
 	subq	%rax, (%rdx)	/* Undo previous adjustment */
 	addq	%rdi, (%rdx)	/* Apply the new adjustment */
 	addq	$8, %rdx
 	jmp	1b
 2:
 	ret

 	.code32
 /*
  * This is the 32-bit trampoline that will be copied over to low memory.
  *
  * RDI contains the return address (might be above 4G).
  * ECX contains the base address of the trampoline memory.
  * Non zero RDX on return means we need to enable 5-level paging.
  */
 ENTRY(trampoline_32bit_src)
 	/* Set up data and stack segments */
 	movl	$__KERNEL_DS, %eax
 	movl	%eax, %ds
 	movl	%eax, %ss

 	/* Set up new stack */
 	leal	TRAMPOLINE_32BIT_STACK_END(%ecx), %esp

 	/* Disable paging */
 	movl	%cr0, %eax
 	btrl	$X86_CR0_PG_BIT, %eax
 	movl	%eax, %cr0

 	/* Check what paging mode we want to be in after the trampoline */
 	cmpl	$0, %edx
 	jz	1f

 	/* We want 5-level paging: don't touch CR3 if it already points to 5-level page tables */
 	movl	%cr4, %eax
 	testl	$X86_CR4_LA57, %eax
 	jnz	3f
 	jmp	2f
 1:
 	/* We want 4-level paging: don't touch CR3 if it already points to 4-level page tables */
 	movl	%cr4, %eax
 	testl	$X86_CR4_LA57, %eax
 	jz	3f
 2:
 	/* Point CR3 to the trampoline's new top level page table */
 	leal	TRAMPOLINE_32BIT_PGTABLE_OFFSET(%ecx), %eax
 	movl	%eax, %cr3
 3:
 	/* Enable PAE and LA57 (if required) paging modes */
 	movl	$X86_CR4_PAE, %eax
 	cmpl	$0, %edx
 	jz	1f
 	orl	$X86_CR4_LA57, %eax
 1:
 	movl	%eax, %cr4

 	/* Calculate address of paging_enabled() once we are executing in the trampoline */
 	leal	paging_enabled - trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_OFFSET(%ecx), %eax

 	/* Prepare the stack for far return to Long Mode */
 	pushl	$__KERNEL_CS
 	pushl	%eax

 	/* Enable paging again */
 	movl	$(X86_CR0_PG | X86_CR0_PE), %eax
 	movl	%eax, %cr0

 	lret

 	.code64
 paging_enabled:
 	/* Return from the trampoline */
 	jmp	*%rdi

 	/*
          * The trampoline code has a size limit.
          * Make sure we fail to compile if the trampoline code grows
          * beyond TRAMPOLINE_32BIT_CODE_SIZE bytes.
 	 */
 	.org	trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_SIZE

 	.code32
 no_longmode:
 	/* This isn't an x86-64 CPU, so hang intentionally, we cannot continue */
 1:
 	hlt
 	jmp     1b

 #include "../../kernel/verify_cpu.S"

 	.data
 gdt64:
 	.word	gdt_end - gdt
 	.long	0
 	.word	0
 	.quad   0
 gdt:
 	.word	gdt_end - gdt
 	.long	gdt
 	.word	0
 	.quad	0x00cf9a000000ffff	/* __KERNEL32_CS */
 	.quad	0x00af9a000000ffff	/* __KERNEL_CS */
 	.quad	0x00cf92000000ffff	/* __KERNEL_DS */
 	.quad	0x0080890000000000	/* TS descriptor */
 	.quad   0x0000000000000000	/* TS continued */
 gdt_end:

 #ifdef CONFIG_EFI_STUB
 efi_config:
 	.quad	0

 #ifdef CONFIG_EFI_MIXED
 	.global efi32_config
 efi32_config:
 	.fill	5,8,0
 	.quad	efi64_thunk
 	.byte	0
 #endif

 	.global efi64_config
 efi64_config:
 	.fill	5,8,0
 	.quad	efi_call
 	.byte	1
 #endif /* CONFIG_EFI_STUB */

 /*
  * Stack and heap for uncompression
  */
 	.bss
 	.balign 4
 boot_heap:
 	.fill BOOT_HEAP_SIZE, 1, 0
 boot_stack:
 	.fill BOOT_STACK_SIZE, 1, 0
 boot_stack_end:

 /*
  * Space for page tables (not in .bss so not zeroed)
  */
 	.section ".pgtable","a",@nobits
 	.balign 4096
 pgtable:
 	.fill BOOT_PGT_SIZE, 1, 0

 /*
  * The page table is going to be used instead of page table in the trampoline
  * memory.
  */
 top_pgtable:
 	.fill PAGE_SIZE, 1, 0
	/* SPDX-License-Identifier: GPL-2.0 */
	/*
	* linux/boot/head.S
	*
	* Copyright (C) 1991, 1992, 1993 Linus Torvalds
	*/

	/*
	* head.S contains the 32-bit startup code.
	*
	* NOTE!!! Startup happens at absolute address 0x00001000, which is also where
	* the page directory will exist. The startup code will be overwritten by
	* the page directory. [According to comments etc elsewhere on a compressed
	* kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
	*
	* Page 0 is deliberately kept safe, since System Management Mode code in
	* laptops may need to access the BIOS data stored there. This is also
	* useful for future device drivers that either access the BIOS via VM86
	* mode.
	*/

	/*
	* High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
	*/
	.code32
	.text

	#include <linux/init.h>
	#include <linux/linkage.h>
	#include <asm/segment.h>
	#include <asm/boot.h>
	#include <asm/msr.h>
	#include <asm/processor-flags.h>
	#include <asm/asm-offsets.h>
	#include <asm/bootparam.h>
	#include "pgtable.h"

	/*
	* Locally defined symbols should be marked hidden:
	*/
	.hidden _bss
	.hidden _ebss
	.hidden _got
	.hidden _egot

	__HEAD
	.code32
	ENTRY(startup_32)
	/*
	* 32bit entry is 0 and it is ABI so immutable!
	* If we come here directly from a bootloader,
	* kernel(text+data+bss+brk) ramdisk, zero_page, command line
	* all need to be under the 4G limit.
	*/
	cld
	/*
	* Test KEEP_SEGMENTS flag to see if the bootloader is asking
	* us to not reload segments
	*/
	testb $KEEP_SEGMENTS, BP_loadflags(%esi)
	jnz 1f

	cli
	movl $(__BOOT_DS), %eax
	movl %eax, %ds
	movl %eax, %es
	movl %eax, %ss
	1:

	/*
	* Calculate the delta between where we were compiled to run
	* at and where we were actually loaded at. This can only be done
	* with a short local call on x86. Nothing else will tell us what
	* address we are running at. The reserved chunk of the real-mode
	* data at 0x1e4 (defined as a scratch field) are used as the stack
	* for this calculation. Only 4 bytes are needed.
	*/
	leal (BP_scratch+4)(%esi), %esp
	call 1f
	1: popl %ebp
	subl $1b, %ebp

	/* setup a stack and make sure cpu supports long mode. */
	movl $boot_stack_end, %eax
	addl %ebp, %eax
	movl %eax, %esp

	call verify_cpu
	testl %eax, %eax
	jnz no_longmode

	/*
	* Compute the delta between where we were compiled to run at
	* and where the code will actually run at.
	*
	* %ebp contains the address we are loaded at by the boot loader and %ebx
	* contains the address where we should move the kernel image temporarily
	* for safe in-place decompression.
	*/

	#ifdef CONFIG_RELOCATABLE
	movl %ebp, %ebx
	movl BP_kernel_alignment(%esi), %eax
	decl %eax
	addl %eax, %ebx
	notl %eax
	andl %eax, %ebx
	cmpl $LOAD_PHYSICAL_ADDR, %ebx
	jge 1f
	#endif
	movl $LOAD_PHYSICAL_ADDR, %ebx
	1:

	/* Target address to relocate to for decompression */
	movl BP_init_size(%esi), %eax
	subl $_end, %eax
	addl %eax, %ebx

	/*
	* Prepare for entering 64 bit mode
	*/

	/* Load new GDT with the 64bit segments using 32bit descriptor */
	addl %ebp, gdt+2(%ebp)
	lgdt gdt(%ebp)

	/* Enable PAE mode */
	movl %cr4, %eax
	orl $X86_CR4_PAE, %eax
	movl %eax, %cr4

	/*
	* Build early 4G boot pagetable
	*/
	/*
	* If SEV is active then set the encryption mask in the page tables.
	* This will insure that when the kernel is copied and decompressed
	* it will be done so encrypted.
	*/
	call get_sev_encryption_bit
	xorl %edx, %edx
	testl %eax, %eax
	jz 1f
	subl $32, %eax /* Encryption bit is always above bit 31 */
	bts %eax, %edx /* Set encryption mask for page tables */
	1:

	/* Initialize Page tables to 0 */
	leal pgtable(%ebx), %edi
	xorl %eax, %eax
	movl $(BOOT_INIT_PGT_SIZE/4), %ecx
	rep stosl

	/* Build Level 4 */
	leal pgtable + 0(%ebx), %edi
	leal 0x1007 (%edi), %eax
	movl %eax, 0(%edi)
	addl %edx, 4(%edi)

	/* Build Level 3 */
	leal pgtable + 0x1000(%ebx), %edi
	leal 0x1007(%edi), %eax
	movl $4, %ecx
	1: movl %eax, 0x00(%edi)
	addl %edx, 0x04(%edi)
	addl $0x00001000, %eax
	addl $8, %edi
	decl %ecx
	jnz 1b

	/* Build Level 2 */
	leal pgtable + 0x2000(%ebx), %edi
	movl $0x00000183, %eax
	movl $2048, %ecx
	1: movl %eax, 0(%edi)
	addl %edx, 4(%edi)
	addl $0x00200000, %eax
	addl $8, %edi
	decl %ecx
	jnz 1b

	/* Enable the boot page tables */
	leal pgtable(%ebx), %eax
	movl %eax, %cr3

	/* Enable Long mode in EFER (Extended Feature Enable Register) */
	movl $MSR_EFER, %ecx
	rdmsr
	btsl $_EFER_LME, %eax
	wrmsr

	/* After gdt is loaded */
	xorl %eax, %eax
	lldt %ax
	movl $__BOOT_TSS, %eax
	ltr %ax

	/*
	* Setup for the jump to 64bit mode
	*
	* When the jump is performend we will be in long mode but
	* in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1
	* (and in turn EFER.LMA = 1). To jump into 64bit mode we use
	* the new gdt/idt that has __KERNEL_CS with CS.L = 1.
	* We place all of the values on our mini stack so lret can
	* used to perform that far jump.
	*/
	pushl $__KERNEL_CS
	leal startup_64(%ebp), %eax
	#ifdef CONFIG_EFI_MIXED
	movl efi32_config(%ebp), %ebx
	cmp $0, %ebx
	jz 1f
	leal handover_entry(%ebp), %eax
	1:
	#endif
	pushl %eax

	/* Enter paged protected Mode, activating Long Mode */
	movl $(X86_CR0_PG \| X86_CR0_PE), %eax /* Enable Paging and Protected mode */
	movl %eax, %cr0

	/* Jump from 32bit compatibility mode into 64bit mode. */
	lret
	ENDPROC(startup_32)

	#ifdef CONFIG_EFI_MIXED
	.org 0x190
	ENTRY(efi32_stub_entry)
	add $0x4, %esp /* Discard return address */
	popl %ecx
	popl %edx
	popl %esi

	leal (BP_scratch+4)(%esi), %esp
	call 1f
	1: pop %ebp
	subl $1b, %ebp

	movl %ecx, efi32_config(%ebp)
	movl %edx, efi32_config+8(%ebp)
	sgdtl efi32_boot_gdt(%ebp)

	leal efi32_config(%ebp), %eax
	movl %eax, efi_config(%ebp)

	jmp startup_32
	ENDPROC(efi32_stub_entry)
	#endif

	.code64
	.org 0x200
	ENTRY(startup_64)
	/*
	* 64bit entry is 0x200 and it is ABI so immutable!
	* We come here either from startup_32 or directly from a
	* 64bit bootloader.
	* If we come here from a bootloader, kernel(text+data+bss+brk),
	* ramdisk, zero_page, command line could be above 4G.
	* We depend on an identity mapped page table being provided
	* that maps our entire kernel(text+data+bss+brk), zero page
	* and command line.
	*/

	/* Setup data segments. */
	xorl %eax, %eax
	movl %eax, %ds
	movl %eax, %es
	movl %eax, %ss
	movl %eax, %fs
	movl %eax, %gs

	/*
	* Compute the decompressed kernel start address. It is where
	* we were loaded at aligned to a 2M boundary. %rbp contains the
	* decompressed kernel start address.
	*
	* If it is a relocatable kernel then decompress and run the kernel
	* from load address aligned to 2MB addr, otherwise decompress and
	* run the kernel from LOAD_PHYSICAL_ADDR
	*
	* We cannot rely on the calculation done in 32-bit mode, since we
	* may have been invoked via the 64-bit entry point.
	*/

	/* Start with the delta to where the kernel will run at. */
	#ifdef CONFIG_RELOCATABLE
	leaq startup_32(%rip) /* - $startup_32 */, %rbp
	movl BP_kernel_alignment(%rsi), %eax
	decl %eax
	addq %rax, %rbp
	notq %rax
	andq %rax, %rbp
	cmpq $LOAD_PHYSICAL_ADDR, %rbp
	jge 1f
	#endif
	movq $LOAD_PHYSICAL_ADDR, %rbp
	1:

	/* Target address to relocate to for decompression */
	movl BP_init_size(%rsi), %ebx
	subl $_end, %ebx
	addq %rbp, %rbx

	/* Set up the stack */
	leaq boot_stack_end(%rbx), %rsp

	/*
	* paging_prepare() and cleanup_trampoline() below can have GOT
	* references. Adjust the table with address we are running at.
	*
	* Zero RAX for adjust_got: the GOT was not adjusted before;
	* there's no adjustment to undo.
	*/
	xorq %rax, %rax

	/*
	* Calculate the address the binary is loaded at and use it as
	* a GOT adjustment.
	*/
	call 1f
	1: popq %rdi
	subq $1b, %rdi

	call adjust_got

	/*
	* At this point we are in long mode with 4-level paging enabled,
	* but we might want to enable 5-level paging or vice versa.
	*
	* The problem is that we cannot do it directly. Setting or clearing
	* CR4.LA57 in long mode would trigger #GP. So we need to switch off
	* long mode and paging first.
	*
	* We also need a trampoline in lower memory to switch over from
	* 4- to 5-level paging for cases when the bootloader puts the kernel
	* above 4G, but didn't enable 5-level paging for us.
	*
	* The same trampoline can be used to switch from 5- to 4-level paging
	* mode, like when starting 4-level paging kernel via kexec() when
	* original kernel worked in 5-level paging mode.
	*
	* For the trampoline, we need the top page table to reside in lower
	* memory as we don't have a way to load 64-bit values into CR3 in
	* 32-bit mode.
	*
	* We go though the trampoline even if we don't have to: if we're
	* already in a desired paging mode. This way the trampoline code gets
	* tested on every boot.
	*/

	/* Make sure we have GDT with 32-bit code segment */
	leaq gdt(%rip), %rax
	movq %rax, gdt64+2(%rip)
	lgdt gdt64(%rip)

	/*
	* paging_prepare() sets up the trampoline and checks if we need to
	* enable 5-level paging.
	*
	* Address of the trampoline is returned in RAX.
	* Non zero RDX on return means we need to enable 5-level paging.
	*
	* RSI holds real mode data and needs to be preserved across
	* this function call.
	*/
	pushq %rsi
	movq %rsi, %rdi /* real mode address */
	call paging_prepare
	popq %rsi

	/* Save the trampoline address in RCX */
	movq %rax, %rcx

	/*
	* Load the address of trampoline_return() into RDI.
	* It will be used by the trampoline to return to the main code.
	*/
	leaq trampoline_return(%rip), %rdi

	/* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */
	pushq $__KERNEL32_CS
	leaq TRAMPOLINE_32BIT_CODE_OFFSET(%rax), %rax
	pushq %rax
	lretq
	trampoline_return:
	/* Restore the stack, the 32-bit trampoline uses its own stack */
	leaq boot_stack_end(%rbx), %rsp

	/*
	* cleanup_trampoline() would restore trampoline memory.
	*
	* RDI is address of the page table to use instead of page table
	* in trampoline memory (if required).
	*
	* RSI holds real mode data and needs to be preserved across
	* this function call.
	*/
	pushq %rsi
	leaq top_pgtable(%rbx), %rdi
	call cleanup_trampoline
	popq %rsi

	/* Zero EFLAGS */
	pushq $0
	popfq

	/*
	* Previously we've adjusted the GOT with address the binary was
	* loaded at. Now we need to re-adjust for relocation address.
	*
	* Calculate the address the binary is loaded at, so that we can
	* undo the previous GOT adjustment.
	*/
	call 1f
	1: popq %rax
	subq $1b, %rax

	/* The new adjustment is the relocation address */
	movq %rbx, %rdi
	call adjust_got

	/*
	* Copy the compressed kernel to the end of our buffer
	* where decompression in place becomes safe.
	*/
	pushq %rsi
	leaq (_bss-8)(%rip), %rsi
	leaq (_bss-8)(%rbx), %rdi
	movq $_bss /* - $startup_32 */, %rcx
	shrq $3, %rcx
	std
	rep movsq
	cld
	popq %rsi

	/*
	* Jump to the relocated address.
	*/
	leaq relocated(%rbx), %rax
	jmp *%rax

	#ifdef CONFIG_EFI_STUB

	/* The entry point for the PE/COFF executable is efi_pe_entry. */
	ENTRY(efi_pe_entry)
	movq %rcx, efi64_config(%rip) /* Handle */
	movq %rdx, efi64_config+8(%rip) /* EFI System table pointer */

	leaq efi64_config(%rip), %rax
	movq %rax, efi_config(%rip)

	call 1f
	1: popq %rbp
	subq $1b, %rbp

	/*
	* Relocate efi_config->call().
	*/
	addq %rbp, efi64_config+40(%rip)

	movq %rax, %rdi
	call make_boot_params
	cmpq $0,%rax
	je fail
	mov %rax, %rsi
	leaq startup_32(%rip), %rax
	movl %eax, BP_code32_start(%rsi)
	jmp 2f /* Skip the relocation */

	handover_entry:
	call 1f
	1: popq %rbp
	subq $1b, %rbp

	/*
	* Relocate efi_config->call().
	*/
	movq efi_config(%rip), %rax
	addq %rbp, 40(%rax)
	2:
	movq efi_config(%rip), %rdi
	call efi_main
	movq %rax,%rsi
	cmpq $0,%rax
	jne 2f
	fail:
	/* EFI init failed, so hang. */
	hlt
	jmp fail
	2:
	movl BP_code32_start(%esi), %eax
	leaq startup_64(%rax), %rax
	jmp *%rax
	ENDPROC(efi_pe_entry)

	.org 0x390
	ENTRY(efi64_stub_entry)
	movq %rdi, efi64_config(%rip) /* Handle */
	movq %rsi, efi64_config+8(%rip) /* EFI System table pointer */

	leaq efi64_config(%rip), %rax
	movq %rax, efi_config(%rip)

	movq %rdx, %rsi
	jmp handover_entry
	ENDPROC(efi64_stub_entry)
	#endif

	.text
	relocated:

	/*
	* Clear BSS (stack is currently empty)
	*/
	xorl %eax, %eax
	leaq _bss(%rip), %rdi
	leaq _ebss(%rip), %rcx
	subq %rdi, %rcx
	shrq $3, %rcx
	rep stosq

	/*
	* Do the extraction, and jump to the new kernel..
	*/
	pushq %rsi /* Save the real mode argument */
	movq %rsi, %rdi /* real mode address */
	leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
	leaq input_data(%rip), %rdx /* input_data */
	movl $z_input_len, %ecx /* input_len */
	movq %rbp, %r8 /* output target address */
	movq $z_output_len, %r9 /* decompressed length, end of relocs */
	call extract_kernel /* returns kernel location in %rax */
	popq %rsi

	/*
	* Jump to the decompressed kernel.
	*/
	jmp *%rax

	/*
	* Adjust the global offset table
	*
	* RAX is the previous adjustment of the table to undo (use 0 if it's the
	* first time we touch GOT).
	* RDI is the new adjustment to apply.
	*/
	adjust_got:
	/* Walk through the GOT adding the address to the entries */
	leaq _got(%rip), %rdx
	leaq _egot(%rip), %rcx
	1:
	cmpq %rcx, %rdx
	jae 2f
	subq %rax, (%rdx) /* Undo previous adjustment */
	addq %rdi, (%rdx) /* Apply the new adjustment */
	addq $8, %rdx
	jmp 1b
	2:
	ret

	.code32
	/*
	* This is the 32-bit trampoline that will be copied over to low memory.
	*
	* RDI contains the return address (might be above 4G).
	* ECX contains the base address of the trampoline memory.
	* Non zero RDX on return means we need to enable 5-level paging.
	*/
	ENTRY(trampoline_32bit_src)
	/* Set up data and stack segments */
	movl $__KERNEL_DS, %eax
	movl %eax, %ds
	movl %eax, %ss

	/* Set up new stack */
	leal TRAMPOLINE_32BIT_STACK_END(%ecx), %esp

	/* Disable paging */
	movl %cr0, %eax
	btrl $X86_CR0_PG_BIT, %eax
	movl %eax, %cr0

	/* Check what paging mode we want to be in after the trampoline */
	cmpl $0, %edx
	jz 1f

	/* We want 5-level paging: don't touch CR3 if it already points to 5-level page tables */
	movl %cr4, %eax
	testl $X86_CR4_LA57, %eax
	jnz 3f
	jmp 2f
	1:
	/* We want 4-level paging: don't touch CR3 if it already points to 4-level page tables */
	movl %cr4, %eax
	testl $X86_CR4_LA57, %eax
	jz 3f
	2:
	/* Point CR3 to the trampoline's new top level page table */
	leal TRAMPOLINE_32BIT_PGTABLE_OFFSET(%ecx), %eax
	movl %eax, %cr3
	3:
	/* Enable PAE and LA57 (if required) paging modes */
	movl $X86_CR4_PAE, %eax
	cmpl $0, %edx
	jz 1f
	orl $X86_CR4_LA57, %eax
	1:
	movl %eax, %cr4

	/* Calculate address of paging_enabled() once we are executing in the trampoline */
	leal paging_enabled - trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_OFFSET(%ecx), %eax

	/* Prepare the stack for far return to Long Mode */
	pushl $__KERNEL_CS
	pushl %eax

	/* Enable paging again */
	movl $(X86_CR0_PG \| X86_CR0_PE), %eax
	movl %eax, %cr0

	lret

	.code64
	paging_enabled:
	/* Return from the trampoline */
	jmp *%rdi

	/*
	* The trampoline code has a size limit.
	* Make sure we fail to compile if the trampoline code grows
	* beyond TRAMPOLINE_32BIT_CODE_SIZE bytes.
	*/
	.org trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_SIZE

	.code32
	no_longmode:
	/* This isn't an x86-64 CPU, so hang intentionally, we cannot continue */
	1:
	hlt
	jmp 1b

	#include "../../kernel/verify_cpu.S"

	.data
	gdt64:
	.word gdt_end - gdt
	.long 0
	.word 0
	.quad 0
	gdt:
	.word gdt_end - gdt
	.long gdt
	.word 0
	.quad 0x00cf9a000000ffff /* __KERNEL32_CS */
	.quad 0x00af9a000000ffff /* __KERNEL_CS */
	.quad 0x00cf92000000ffff /* __KERNEL_DS */
	.quad 0x0080890000000000 /* TS descriptor */
	.quad 0x0000000000000000 /* TS continued */
	gdt_end:

	#ifdef CONFIG_EFI_STUB
	efi_config:
	.quad 0

	#ifdef CONFIG_EFI_MIXED
	.global efi32_config
	efi32_config:
	.fill 5,8,0
	.quad efi64_thunk
	.byte 0
	#endif

	.global efi64_config
	efi64_config:
	.fill 5,8,0
	.quad efi_call
	.byte 1
	#endif /* CONFIG_EFI_STUB */

	/*
	* Stack and heap for uncompression
	*/
	.bss
	.balign 4
	boot_heap:
	.fill BOOT_HEAP_SIZE, 1, 0
	boot_stack:
	.fill BOOT_STACK_SIZE, 1, 0
	boot_stack_end:

	/*
	* Space for page tables (not in .bss so not zeroed)
	*/
	.section ".pgtable","a",@nobits
	.balign 4096
	pgtable:
	.fill BOOT_PGT_SIZE, 1, 0

	/*
	* The page table is going to be used instead of page table in the trampoline
	* memory.
	*/
	top_pgtable:
	.fill PAGE_SIZE, 1, 0