offsets_target.h File Reference

X86-64 address space sizes and offsets. More...

Macros
#define	X86_64_VADDR_SPACE_BITS   48
#define	X86_64_PADDR_SPACE_BITS   48
#define	X86_64_START_KERNEL_PHYS   0x100000
#define	X86_64_KERNEL_STACK_SIZE   0x4000
#define	X86_64_PADDR_SPACE_LIMIT   ((genpaddr_t)1 << 40)
#define	X86_64_INIT_SPACE_LIMIT   (32 * 1024 * 1024)
#define	X86_64_INIT_VBASE   0x200000
#define	X86_64_KERNEL_INIT_MEMORY   (1 * 1024 * 1024)
#define	X86_64_PML4_ALIGN(addr)   ((addr) & ((genpaddr_t)0x7fffff << 41))
#define	X86_64_MEMORY_OFFSET   X86_64_PML4_ALIGN(-X86_64_PADDR_SPACE_LIMIT)
#define	X86_64_REAL_MODE_SEGMENT   0x0600
#define	X86_64_REAL_MODE_OFFSET   0x0000
#define	X86_64_REAL_MODE_LINEAR_OFFSET   (X86_64_REAL_MODE_SEGMENT << 4)

Variables
uintptr_t	x86_64_kernel_stack [X86_64_KERNEL_STACK_SIZE/sizeof(uintptr_t)]
	The kernel stack. More...

Detailed Description

X86-64 address space sizes and offsets.

The layout of the x86-64 virtual address space can be summarized as follows:

 +----------------------------------------------------+-----------------+
 | User-space                                         | Physical memory |
 | PML4 entries: 0 1 2 3 4 ... 510                    | 511             |
 +----------------------------------------------------+-----------------+

User-space maps user-space programs. Physical memory maps all available physical memory (up to PADDR_SPACE_LIMIT).

This partition is static and can only be changed at compile-time.

Physical memory can grow downwards, towards user-space, although it is expected to stay within PML4 entry 511 for quite some time (one PML4 entry can map 512 GBytes). The rest of the address space can be freely mapped by (possibly multiple) user-space programs.

Macro Definition Documentation

#define X86_64_INIT_SPACE_LIMIT   (32 * 1024 * 1024)

Static address space limit for the init user-space domain. The static space is used to map in code and static data of the init module, as well as all loaded multiboot modules. init can freely allocate dynamic memory as soon as it is running. This is 32 MBytes right now.

You should make this constant a multiple of #BASE_PAGE_SIZE * #PTABLE_SIZE or you'll restrict init's static address space unneccessarily. init's lowest segment should also be based at these multiples or it restricts itself.

#define X86_64_INIT_VBASE   0x200000

Base address of init address space in virtual memory. init should start at 4 MByte. The kernel maps in important structures at 2 MByte. This address should be page-table size aligned (i.e. with 4 KByte pages, a page table maps 2 MBytes. Thus, align it to multiples of 2 MBytes).

#define X86_64_KERNEL_INIT_MEMORY   (1 * 1024 * 1024)

Initial amount of physical memory to map during bootup. The low 1MByte of memory is always expected to be there and has to be specified here at minimum. If you need more during bootup, increase this value. This value is also the amount of memory you expect to be in the system during bootup, or the kernel will crash!

#define X86_64_KERNEL_STACK_SIZE   0x4000

Kernel stack size – 16KB

#define X86_64_MEMORY_OFFSET   X86_64_PML4_ALIGN(-X86_64_PADDR_SPACE_LIMIT)

Absolute offset of mapped physical memory within virtual address space. This occupies one or more (usually one) PML4 slots directly before the kernel. This needs to be aligned to PADDR_SPACE_LIMIT.

Change VSPACE_END in lib/barrelfish if you change this.

#define X86_64_PADDR_SPACE_BITS   48

Absolute size of physical address space. This is also 48-bit.

#define X86_64_PADDR_SPACE_LIMIT   ((genpaddr_t)1 << 40)

Maximum physical address space mappable by the kernel. Adjust this for a bigger physical address space. We set this to 40-bit, i.e. 1 TByte.

#define X86_64_PML4_ALIGN

(

addr

)

((addr) & ((genpaddr_t)0x7fffff << 41))

Aligns an address to the nearest PML4 entry by masking out lower 41 bits.

#define X86_64_REAL_MODE_LINEAR_OFFSET   (X86_64_REAL_MODE_SEGMENT << 4)

The linear offset of the real-mode segment

#define X86_64_REAL_MODE_OFFSET   0x0000

The real-mode offset has to be 0000!!

#define X86_64_REAL_MODE_SEGMENT   0x0600

The real-mode addressesThe real-mode segment

#define X86_64_START_KERNEL_PHYS   0x100000

Start address of kernel image in physical memory. This is passed to the linker also. The bootloader will load us there.

#define X86_64_VADDR_SPACE_BITS   48

Absolute size of virtual address space. This is 48-bit on x86-64 currently, which equals 256 TBytes and allows for 512 PML4 slots, each of which can map 512 GBytes.

Variable Documentation

uintptr_t x86_64_kernel_stack[X86_64_KERNEL_STACK_SIZE/sizeof(uintptr_t)]

The kernel stack.

The kernel stack.

This is the one and only kernel stack for a kernel instance.