/* 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
        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