55 lines
2.7 KiB
Markdown
55 lines
2.7 KiB
Markdown
# x86_64 Virtual Memory Layout
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┌─────────────────────┐ 0xFFFFFFFF_FFFFFFFF
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│ Higher Half │
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├─────────────────────┤ 0xFFFFFFFF_FF600000
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│ Recursive │ (Optional: for page table manipulation)
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│ Page Mapping │
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├─────────────────────┤ 0xFFFFFFFF_C0000000
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│ Kernel Stacks │ (Multiple 16KB or 32KB stacks, guard pages between)
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├─────────────────────┤
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│ Kernel Heap │ (Dynamic allocation for kernel)
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├─────────────────────┤ 0xFFFFFFFF_80000000
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│ Kernel Code │ (Loaded by bootloader)
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├─────────────────────┤ 0x00007FFF_FFFFFFFF
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│ Guard │ (Prevent user->kernel pointer errors)
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├─────────────────────┤ 0x00007FFF_00000000
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│ User Stacks │ (Grows down)
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├─────────────────────┤
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│ ... │ (Available for mmap, shared libraries, etc.)
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├─────────────────────┤
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│ User Heap │ (Grows up)
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├─────────────────────┤
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│ Program .bss │ (Uninitialized data)
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│ Program .data │ (Initialized data)
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│ Program .rodata │ (Read-only data)
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│ Program .text │ (Code)
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├─────────────────────┤ 0x0000000000400000
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│ Guard │ (Catch null pointer dereference)
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└─────────────────────┘ 0x0000000000000000
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## Memory Regions Explanation
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### Kernel Space (Higher Half)
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- **Kernel Code**: Fixed location at -2GB
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- **Kernel Heap**: Dynamic memory for kernel operations
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- **Kernel Stacks**: Multiple stacks for different CPU modes/tasks
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- **Recursive Mapping**: Optional region for page table manipulation
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### User Space (Lower Half)
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- **Guard Pages**: Protect against null pointer dereference (0-4MB)
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- **Program Sections**: Start at 0x400000
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- .text: Program code
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- .rodata: Read-only data
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- .data: Initialized data
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- .bss: Uninitialized data
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- **User Heap**: Grows upward from end of program sections
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- **Dynamic Region**: Space for mmap allocations, shared libraries
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- **User Stacks**: Grows downward from 0x00007FFF_00000000
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### Key Features
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- Full 48-bit addressing support (256TB virtual address space)
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- Clear separation between user and kernel space
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- Protected null pointer dereference
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- Room for stack/heap growth
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- Space for dynamic libraries and mappings |