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/*
*
* Copyright 2024 Google Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/*
* For reference see "AMD64 Architecture Programmer's Manual Volume 2",
* Document 24593-Rev. 3.31-July 2019 Chapter 5.3.4
*
* Page table attributes: WB, User+Supervisor, Present, Writeable, Accessed, Dirty
*/
.section .bss
#define _PRES (1ULL << 0)
#define _RW (1ULL << 1)
#define _US (1ULL << 2)
#define _A (1ULL << 5)
#define _D (1ULL << 6)
#define _PS (1ULL << 7)
.section .bss.pm4le
.global pm4le
.align 4096
pm4le:
.skip 8
.section .bss.main_page_table
.global main_page_table
.align 4096
main_page_table:
.skip 8192
.section .bss.extra_page_table
.global extra_page_table
.align 4096
extra_page_table:
.skip 32
/*
* WARNING: 32-bit/64-bit Mode Compatibility for Page Table Initialization
* This `init_page_table` function is designed to work in both 32-bit protected
* mode AND 64-bit long mode.
*
* Key Considerations:
* - Assembly Instructions: Use ONLY instructions that have the SAME binary representation
* in both 32-bit and 64-bit modes.
* - `.code64` Directive: We're compiling with `.code64` to ensure the assembler uses
* the correct 64-bit version of instructions (e.g., `inc`).
* - Register Notation:
* - Use 64-bit register names (like `%rsi`) for register-indirect addressing to avoid
* incorrect address size prefixes.
* - It's safe to use `%esi` with `mov` instructions, as the high 32 bits are zeroed
* in 64-bit mode.
*
* IMPORTANT:
* Thoroughly test ANY changes to this function in BOTH 32-bit and 64-bit boot environments.
*/
.code64
.section .text.init_page_table
.globl init_page_table
.type init_page_table, @function
init_page_table:
mov $0x80000001, %eax
cpuid
test $(1 << 26), %edx
jnz setup_1gb
setup_2mb:
mov $2048, %edi
mov $(_PRES + _RW + _US + _PS + _A + _D), %eax
mov $0, %ecx
mov $main_page_table, %esi
loop_2mb:
mov %eax, (%rsi, %rcx, 8)
mov $0, 4(%rsi, %rcx, 8)
add $0x200000, %eax
inc %ecx
cmp %edi, %ecx
jb loop_2mb
mov $4, %edi
mov $main_page_table, %eax
add $(_PRES + _RW + _US + _A), %eax
mov $0, %ecx
mov $extra_page_table, %esi
fill_extra_page_table:
mov %eax, (%rsi, %rcx, 8)
mov $0, 4(%rsi, %rcx, 8)
add $4096, %eax
inc %ecx
cmp %edi, %ecx
jb fill_extra_page_table
mov $extra_page_table, %eax
jmp leave
setup_1gb:
mov $512, %edi
mov $(_PRES + _RW + _US + _PS + _A + _D), %eax
mov $0, %ebx
mov $0, %ecx
mov $main_page_table, %esi
loop_1gb:
mov %eax, (%rsi, %rcx, 8)
mov %ebx, 4(%rsi, %rcx, 8)
add $0x40000000, %eax
cmp $0x40000000, %eax
ja no_overflow_1gb
inc %ebx
no_overflow_1gb:
inc %ecx
cmp %edi, %ecx
jb loop_1gb
mov $main_page_table, %eax
leave:
or $(_PRES + _RW + _US + _A), %eax
mov %eax, pm4le
ret
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