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Coppy original mapping to the higher half

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This commit is contained in:
Eugen Wissner
2025-07-30 23:11:12 +02:00
parent eac9236e44
commit d12bfbcd43
3 changed files with 266 additions and 242 deletions
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17
Rakefile
View File

@@ -144,11 +144,13 @@ namespace :cross do
cwd = source_directory.dirname + 'build-binutils'
cwd.mkpath
options.rootfs.mkpath
options.sysroot.mkpath
env = ENV.slice 'CC', 'CXX'
configure_options = [
"--prefix=#{options.rootfs.realpath}",
"--target=#{options.target}",
"--with-sysroot=#{options.sysroot.realpath}",
'--disable-nls',
'--enable-gprofng=no',
'--disable-werror',
@@ -167,7 +169,6 @@ namespace :cross do
cwd = source_directory.dirname + 'build-gcc'
cwd.mkpath
options.rootfs.mkpath
options.sysroot.mkpath
sh 'contrib/download_prerequisites', chdir: source_directory.to_path
configure_options = options.configuration('-with-') + [
@@ -354,10 +355,10 @@ rule '.elna.o' => ->(match) {
} do |t|
options = BuildTarget.new relative_from_tmp(t.name).first
compiler = options.rootfs + "bin/#{options.target}-gcc"
flags = ['-O2', '-g3', '-fno-stack-protector'] + options.configuration('m')
sources = t.prerequisites.select { |prerequisite| File.extname(prerequisite) == '.elna' }
system compiler.to_s, *flags, '-c', '-o', t.name, *sources, exception: true
system compiler.to_s, '-O2', '-g3', '-fno-stack-protector', *options.configuration('m'),
'-c', '-o', t.name, *sources, exception: true
end
rule 'kernel.elf' => ->(match) {
@@ -373,17 +374,17 @@ rule 'kernel.elf' => ->(match) {
objects << "arch/#{instruction_set}/kernel.ld"
} do |t|
options = BuildTarget.new relative_from_tmp(t.name).first
compiler = options.rootfs + "bin/#{options.target}-gcc"
flags = options.configuration('m')
linker = options.rootfs + options.target + 'bin/ld'
objects, linker_script = t.prerequisites.partition { |prerequisite| File.extname(prerequisite) == '.o' }
system compiler.to_s, '-nostdlib', '-T', *linker_script, '-o', t.name, *objects, exception: true
system linker.to_s, '-nostdlib', '-T', *linker_script, '-o', t.name, *objects, exception: true
end
task default: 'build/riscv32/kernel.elf'
task :default do |t|
QEMU = 'qemu-system-riscv32'
system QEMU, '-machine', 'virt', '-bios', 'default', '-nographic', '-serial', 'mon:stdio', '--no-reboot',
'-kernel', t.prerequisites.last, exception: true
system QEMU, '-machine', 'virt', '-nographic', '-serial', 'mon:stdio', '--no-reboot',
'-bios', '../opensbi-1.7-rv-bin/share/opensbi/ilp32/generic/firmware/fw_jump.bin',
'-device', "loader,file=#{t.prerequisites.last}", exception: true
end

23
arch/riscv/kernel.ld
View File

@@ -1,23 +1,20 @@
OUTPUT_ARCH("riscv")
OUTPUT_FORMAT("elf32-littleriscv")
ENTRY(_entry)
ENTRY(_start)
PHDRS {
boot PT_LOAD FLAGS(5);
text PT_LOAD FLAGS(5);
data PT_LOAD FLAGS(6);
}
SECTIONS {
.text.boot 0x80200000 : {
_kernel_base = 0x80400000;
_kernel_virtual = 0xc0000000;
_kernel_offset = _kernel_virtual - _kernel_base;
.text _kernel_virtual : AT(ADDR(.text) - _kernel_offset) {
KEEP(*(.text.boot));
. = ALIGN(CONSTANT(MAXPAGESIZE));
ASSERT(. - ADDR(.text.boot) == 0x1000, "error: stub larger than one page");
} :boot
_kernel_offset = 0x3fdff000;
.text 0xc0000000 : AT(ADDR(.text) - _kernel_offset) {
PROVIDE(__executable_start = . - _kernel_offset);
ASSERT(. - ADDR(.text) <= 0x1000, "error: stub larger than one page");
*(.text .text.*);
} :text
@@ -33,10 +30,10 @@ SECTIONS {
.data : AT(ADDR(.data) - _kernel_offset) ALIGN(16) {
*(.data .data.*);
}
} :data
.bss (NOLOAD) : {
PROVIDE(__bss_start = . - _kernel_offset);
PROVIDE(__bss_start = .);
*(.bss .bss.* .sbss .sbss.*);
}

468
arch/riscv/kernel.s
View File

@@ -1,10 +1,253 @@
.global _entry
.section .rodata
panic_message: .asciz "\nPanic"
.equ PANIC_MESSAGE_SIZE, . - panic_message
.section .text.boot
.type _start, @function
.global _start
_start:
mv s1, a1 # Save the device tree pointer.
auipc s2, 0 # Save the physical start of the text section.
# Set the stack pointer.
lui sp, %hi(end)
addi sp, sp, %lo(end)
li t0, 64 * 1024
add sp, sp, t0
mv a0, s2
mv a1, sp
jal imem_initialize
jal imem_mirror
la a0, __bss_start
la a1, end
call bzero
lui t0, %hi(trap_routine)
addi t0, t0, %lo(trap_routine)
csrw stvec, t0
mv a0, sp
mv a1, s1
lui t0, %hi(kernel_main)
jr t0, %lo(kernel_main)
# Copies the identity mappings to the higher half.
.type imem_mirror, @function
imem_mirror:
csrr t0, satp
slli t0, t0, 12
li t3, 0x1000
add t1, t0, t3 # Original page table.
add t2, t1, t3 # Copied page table.
mv t3, t2
.Limem_mirror_copy:
lw t4, (t1)
sw t4, (t3)
addi t3, t3, 4
addi t1, t1, 4
blt t1, t2, .Limem_mirror_copy
# Persist the copied page table in the root page table.
lui t4, %hi(_start)
srli t4, t4, 20 # VPN[1] * PTESIZE.
add t4, t0, t4 # a + VPN[1] * PTESIZE.
srli t3, t2, 2
ori t3, t3, 0b1
sw t3, (t4)
ret
# Activates paging and creates root page table.
# Allocates enough pages for the kernel and its stack.
#
# Parameters:
# a0 - Physical start of the text section.
# a1 - Page aligned address following the kernel (kernel end).
.type imem_initialize, @function
imem_initialize:
# Prologue.
addi sp, sp, -32
sw ra, 28(sp)
sw s0, 24(sp)
addi s0, sp, 32
sw a1, 20(sp)
sw s1, 16(sp)
sw s2, 12(sp)
sw s3, 8(sp)
li s1, 4096
add s1, a1, s1
# Set boundaries between segments.
lui s2, %hi(etext)
lui s3, %hi(_data)
# Set the root page since it is used by mapping functions,
# but don't activate paging before the segments are property mapped.
srli t0, a1, 12
csrw satp, t0
# Executable section.
# a0 is coming from the parameter.
addi a1, s2, %lo(etext)
mv a2, s1
li a3, 1
li a4, 0b1010
jal imem_map_range
# Read only section.
addi a0, s2, %lo(etext)
addi a1, s3, %lo(_data)
mv a2, s1
li a3, 1
li a4, 0b0010
jal imem_map_range
# Data section.
addi a0, s3, %lo(_data)
lw a1, 20(sp)
li t0, 4096 * 3
add a1, a1, t0
mv a2, s1
li a3, 1
li a4, 0b0110
jal imem_map_range
# Enable paging.
csrr t0, satp
li t1, 0x80000000
or t0, t0, t1
sfence.vma
csrw satp, t0
sfence.vma
lw s3, 8(sp)
lw s2, 12(sp)
lw s1, 16(sp)
# Epilogue.
lw ra, 28(sp)
lw s0, 24(sp)
addi sp, sp, 32
ret
# Maps multiple pages of physical memory to the identical virtual memory.
#
# Parameters:
# a0 - Start address.
# a1 - End address.
# a2 - Start of the free memory that can be used to create leaf page tables.
# a3 - Page table level. If a3 is 0 a superpage is allocated, otherwise a normal page.
# a4 - Flags.
.type imem_map_range, @function
imem_map_range:
# Prologue.
addi sp, sp, -32
sw ra, 28(sp)
sw s0, 24(sp)
addi s0, sp, 32
sw s1, 20(sp)
sw a2, 16(sp)
sw a3, 12(sp)
sw a4, 8(sp)
mv s1, a1
.Limem_map_range_loop:
bge a0, s1, .Limem_map_range_end
mv a1, a0
lw a2, 16(sp)
lw a3, 12(sp)
lw a4, 8(sp)
jal imem_map_at
li t0, 4096
add a0, a0, t0
j .Limem_map_range_loop
.Limem_map_range_end:
lw s1, 20(sp)
# Epilogue.
lw ra, 28(sp)
lw s0, 24(sp)
addi sp, sp, 32
ret
# Maps a page of physical memory to the identical virtual memory.
#
# Parameters:
# a0 - Corresponding virtual address.
# a1 - Physical page address.
# a2 - Free memory page that can be used to create a leaf page table.
# a3 - Page table level. If a3 is 0 a superpage is allocated, otherwise a normal page.
# a4 - Flags.
#
# Returns virtual page address in a0.
.type imem_map_at, @function
imem_map_at:
csrr t0, satp
slli t0, t0, 12 # Root table address.
li t4, 0xfffffc00
li t5, 0xffc # 10 bit * PTESIZE mask.
li t1, 20
.Limem_map_at_loop:
# Multiply VPN[i] by 4 and add to the start address of the page table.
# This gives the physical address of the page table entry.
srl t2, a0, t1
and t2, t2, t5 # VPN[i] * PTESIZE.
add t2, t0, t2 # a + VPN[i] * PTESIZE.
beqz a3, .Limem_map_at_leaf
lw t3, (t2)
andi t6, t3, 0b1
beqz t6, .Limem_map_at_create
and t0, t3, t4
slli t0, t0, 2
j .Limem_map_at_next
.Limem_map_at_create:
# Take a chunk of free memory and use it as the next page table.
# The beginning addres off the chunk is the base address (a) for the next level.
mv t0, a2
srli t3, t0, 2
ori t3, t3, 0b1
sw t3, (t2)
.Limem_map_at_next:
# Calculate the next page table address for the next level.
addi t1, t1, -10
addi a3, a3, -1
j .Limem_map_at_loop
.Limem_map_at_leaf:
srli t3, a1, 2 # Physical page number mapped to 12 bits of the page table entry.
ori a4, a4, 0b1
or t3, t3, a4 # Execute, write, read and valid.
sw t3, (t2)
ret
.section .text
.type kernel_main, @function
@@ -18,9 +261,6 @@ kernel_main:
sw a0, 20(sp)
sw a1, 16(sp)
la t0, kernel_entry
csrw stvec, t0
# Map flat device tree to the virtual memory.
lw a0, 16(sp)
li t0, 0xffc00000
@@ -45,8 +285,8 @@ kernel_main:
ret
.balign 4
.type kernel_entry, @function
kernel_entry:
.type trap_routine, @function
trap_routine:
csrw sscratch, sp
addi sp, sp, -4 * 31
@@ -184,217 +424,3 @@ panic:
lw s0, 24(sp)
addi sp, sp, 32
ret
.section .text.boot
_entry:
# Set the stack pointer.
la t0, end
li t1, 64 * 1024
add sp, t0, t1
mv s1, a1
mv a0, sp
call imem_initialize
li s2, 0xc0000000
li s3, 0x80201000
li s4, 0x1000
.rept 12
mv a0, s2
mv a1, s3
li t0, 8192
add a2, sp, t0
li a3, 1
li a4, 0b1110
call imem_map_at
add s2, s2, s4
add s3, s3, s4
.endr
la a0, __bss_start
la a1, end
call bzero
mv a0, sp
mv a1, s1
tail kernel_main
# Activates paging and creates root page table.
# Allocates enough pages for the kernel and its stack.
#
# Parameters:
# a0 - Page aligned address following the kernel (kernel end).
.type imem_initialize, @function
imem_initialize:
# Prologue.
addi sp, sp, -32
sw ra, 28(sp)
sw s0, 24(sp)
addi s0, sp, 32
sw a0, 20(sp)
srli t0, a0, 12
csrw satp, t0
la a0, .text.boot
mv a1, a0
lw a2, 20(sp)
li t0, 4096
add a2, a2, t0
li a3, 1
li a4, 0b1010
call imem_map_at
la a0, __executable_start
la a1, etext
lw a2, 20(sp)
li t0, 4096
add a2, a2, t0
li a3, 1
li a4, 0b1010
call imem_map_range
la a0, etext
la a1, _data
lw a2, 20(sp)
li t0, 4096
add a2, a2, t0
li a3, 1
li a4, 0b0010
call imem_map_range
la a0, _data
lw a1, 20(sp)
li t0, 4096
add a1, a1, t0
add a1, a1, t0
add a1, a1, t0
add a2, a1, t0
li a3, 1
li a4, 0b0110
call imem_map_range
csrr t0, satp
li t1, 0x80000000
or t0, t0, t1
sfence.vma
csrw satp, t0
sfence.vma
# Epilogue.
lw ra, 28(sp)
lw s0, 24(sp)
addi sp, sp, 32
ret
# Maps multiple pages of physical memory to the identical virtual memory.
#
# Parameters:
# a0 - Start address.
# a1 - End address.
# a2 - Start of the free memory that can be used to create leaf page tables.
# a3 - Page table level. If a3 is 0 a superpage is allocated, otherwise a normal page.
# a4 - Flags.
.type imem_map_range, @function
imem_map_range:
# Prologue.
addi sp, sp, -32
sw ra, 28(sp)
sw s0, 24(sp)
addi s0, sp, 32
sw s1, 20(sp)
sw a2, 16(sp)
sw a3, 12(sp)
sw a4, 8(sp)
mv s1, a1
.Limem_map_range_loop:
bge a0, s1, .Limem_map_range_end
mv a1, a0
lw a2, 16(sp)
lw a3, 12(sp)
lw a4, 8(sp)
call imem_map_at
li t0, 4096
add a0, a0, t0
j .Limem_map_range_loop
.Limem_map_range_end:
lw s1, 20(sp)
# Epilogue.
lw ra, 28(sp)
lw s0, 24(sp)
addi sp, sp, 32
ret
# Maps a page of physical memory to the identical virtual memory.
#
# Parameters:
# a0 - Physical page address.
# a1 - Corresponding virtual address.
# a2 - Free memory page that can be used to create a leaf page table.
# a3 - Page table level. If a3 is 0 a superpage is allocated, otherwise a normal page.
# a4 - Flags.
#
# Returns virtual page address in a0.
.type imem_map_at, @function
imem_map_at:
csrr t0, satp
slli t0, t0, 12 # Root table address.
li t4, 0xfffffc00
li t5, 0xffc # 10 bit * PTESIZE mask.
li t1, 20
.Limem_map_at_loop:
# Multiply VPN[i] by 4 and add to the start address of the page table.
# This gives the physical address of the page table entry.
srl t2, a0, t1
and t2, t2, t5 # VPN[i] * PTESIZE.
add t2, t0, t2 # a + VPN[i] * PTESIZE.
beqz a3, .Limem_map_at_leaf
lw t3, (t2)
andi t6, t3, 0b1
beqz t6, .Limem_map_at_create
and t0, t3, t4
slli t0, t0, 2
j .Limem_map_at_next
.Limem_map_at_create:
# Take a chunk of free memory and use it as the next page table.
# The beginning addres off the chunk is the base address (a) for the next level.
mv t0, a2
srli t3, t0, 2
ori t3, t3, 0b1
sw t3, (t2)
.Limem_map_at_next:
# Calculate the next page table address for the next level.
addi t1, t1, -10
addi a3, a3, -1
j .Limem_map_at_loop
.Limem_map_at_leaf:
srli t3, a1, 2 # Physical page number mapped to 12 bits of the page table entry.
ori a4, a4, 0b1
or t3, t3, a4 # Execute, write, read and valid.
sw t3, (t2)
ret