Make data sections not executable
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@@ -12,7 +12,9 @@ SECTIONS {
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KEEP(*(.text.boot));
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*(.text .text.*);
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} :text
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PROVIDE(estart = .);
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. = ALIGN(CONSTANT(MAXPAGESIZE));
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PROVIDE(etext = .);
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.rodata : ALIGN(16) {
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*(.rodata .rodata.*);
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@@ -25,6 +25,7 @@ bzero:
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# a0 - Physical page address.
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# a1 - Free memory page that can be used to create a leaf page table.
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# a2 - Page table level. If a2 is 0 a superpage is allocated, otherwise a normal page.
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# a3 - Flags.
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#
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# Returns virtual page address in a0.
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.type imem_map_at, @function
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@@ -32,43 +33,101 @@ imem_map_at:
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csrr t0, satp
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slli t0, t0, 12 # Root table address.
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li t1, 0xffc # 10 bit * PTESIZE mask.
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srli t4, a0, 2 # Physical page number.
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li t4, 0xfffffc00
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li t5, 0xffc # 10 bit * PTESIZE mask.
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li t1, 20
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# Multiply VPN[1] by 4 and add to the start address of the page table.
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.Limem_map_at_loop:
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# Multiply VPN[i] by 4 and add to the start address of the page table.
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# This gives the physical address of the page table entry.
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srli t2, a0, 20
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and t2, t2, t1 # VPN[1] * PTESIZE.
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add t2, t0, t2 # a + VPN[1] * PTESIZE.
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srl t2, a0, t1
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and t2, t2, t5 # VPN[i] * PTESIZE.
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add t2, t0, t2 # a + VPN[i] * PTESIZE.
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beqz a2, .Limem_map_at_super
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beqz a2, .Limem_map_at_leaf
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srli t3, a1, 2
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lw t3, (t2)
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andi t6, t3, 0b1
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beqz t6, .Limem_map_at_create
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and t0, t3, t4
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slli t0, t0, 2
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j .Limem_map_at_next
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.Limem_map_at_create:
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# Take a chunk of free memory and use it as the next page table.
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# The beginning addres off the chunk is the base address (a) for the next level.
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mv t0, a1
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srli t3, t0, 2
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ori t3, t3, 0b1
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sw t3, (t2)
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srli t2, a0, 10
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and t2, t2, t1 # VPN[0] * PTESIZE.
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add t2, a1, t2 # a + VPN[0] * PTESIZE.
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.Limem_map_at_next:
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# Calculate the next page table address for the next level.
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addi t1, t1, -10
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addi a2, a2, -1
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j .Limem_map_at_leaf
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.Limem_map_at_super:
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# Calculate PPN[1] (10 most significant bits of the physical address
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# and map it to 12 bits of the table page entry.
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li t1, 0xfff00000
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and t4, t4, t1
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j .Limem_map_at_loop
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.Limem_map_at_leaf:
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ori t4, t4, 0b1111 # Execute, write, read and valid.
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sw t4, (t2)
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srli t3, a0, 2 # Physical page number mapped to 12 bits of the page table entry.
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ori a3, a3, 0b1
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or t3, t3, a3 # Execute, write, read and valid.
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sw t3, (t2)
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ret
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# Maps multiple pages of physical memory to the identical virtual memory.
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#
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# Parameters:
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# a0 - Start address.
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# a1 - End address.
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# a2 - Start of the free memory that can be used to create leaf page tables.
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# a3 - Page table level. If a2 is 0 a superpage is allocated, otherwise a normal page.
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# a4 - Flags.
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.type imem_map_range, @function
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imem_map_range:
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# Prologue.
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addi sp, sp, -32
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sw ra, 28(sp)
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sw s0, 24(sp)
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addi s0, sp, 32
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sw s1, 20(sp)
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sw a2, 16(sp)
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sw a3, 12(sp)
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sw a4, 8(sp)
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mv s1, a1
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.Limem_map_range_loop:
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bge a0, s1, .Limem_map_range_end
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lw a1, 16(sp)
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lw a2, 12(sp)
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lw a3, 8(sp)
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call imem_map_at
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li t0, 4096
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add a0, a0, t0
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j .Limem_map_range_loop
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.Limem_map_range_end:
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lw s1, 20(sp)
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# Epilogue.
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lw ra, 28(sp)
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lw s0, 24(sp)
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addi sp, sp, 32
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ret
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# Activates paging and creates root page table.
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# Allocates enough pages for the kernel and its stack.
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#
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# Parameters:
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#
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# a0 - Start (base) address of the kernel.
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# a1 - Page aligned address following the kernel (kernel end).
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.type imem_initialize, @function
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@@ -79,31 +138,30 @@ imem_initialize:
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sw s0, 24(sp)
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addi s0, sp, 32
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li t0, 64 * 1024
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add t0, a1, t0
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sw t0, 20(sp)
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sw a0, 20(sp)
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sw a1, 16(sp)
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srli t0, a1, 12
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csrw satp, t0
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.Limem_initialize_loop:
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lw t0, 20(sp)
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la a0, .text.boot
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la a1, etext
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lw a2, 16(sp)
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li t0, 4096
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add a2, a2, t0
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li a3, 1
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li a4, 0b1010
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call imem_map_range
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la a0, etext
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lw a1, 16(sp)
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bge a0, t0, .Limem_initialize_activate
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li t0, 4096
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add a1, a1, t0
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li a2, 1
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call imem_map_at
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add a2, a1, t0
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li a3, 1
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li a4, 0b0110
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call imem_map_range
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li t0, 4096
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add a0, a0, t0
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j .Limem_initialize_loop
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.Limem_initialize_activate:
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csrr t0, satp
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li t1, 0x80000000
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or t0, t0, t1
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@@ -134,8 +192,11 @@ kernel_main:
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# Map flat device tree to the virtual memory.
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lw a0, 16(sp)
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li t0, 0xffc00000
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and a0, a0, t0
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lw a1, 20(sp)
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li a2, 0
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li a3, 0b0010
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call imem_map_at
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lw a0, 16(sp)
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