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CONFIG_KERNEL_VM_BASE
¶
Base virtual address to link the kernel
Type: hex
Help¶
Define the base virtual memory address for the core kernel.
The kernel expects a mappings for all physical RAM regions starting at this virtual address, with any unused space up to the size denoted by KERNEL_VM_SIZE available for memory mappings. This base address denotes the start of the RAM mapping and may not be the base address of the kernel itself, but the offset of the kernel here will be the same as the offset from the beginning of physical memory where it was loaded.
If there are multiple physical RAM regions which are discontinuous in the physical memory map, they should all be mapped in a continuous virtual region, with bounds defined by KERNEL_RAM_SIZE.
By default, this is the same as the DT_CHOSEN_Z_SRAM physical base SRAM address from DTS, in which case RAM will be identity-mapped. Some architectures may require RAM to be mapped in this way; they may have just one RAM region and doing this makes linking much simpler, as at least when the kernel boots all virtual RAM addresses are the same as their physical address (demand paging at runtime may later modify this for some subset of non-pinned pages).
Otherwise, if RAM isn’t identity-mapped: 1. It is the architecture’s responsibility to transition the instruction pointer to virtual addresses at early boot before entering the kernel at z_cstart(). 2. The underlying architecture may impose constraints on the bounds of the kernel’s address space, such as not overlapping physical RAM regions if RAM is not identity-mapped, or the virtual and physical base addresses being aligned to some common value (which allows double-linking of paging structures to make the instruction pointer transition simpler).
Default¶
0x0
Kconfig definition¶
At <Zephyr>/arch/Kconfig:592
Included via <Zephyr>/Kconfig:8
→ <Zephyr>/Kconfig.zephyr:29
Menu path: (Top) → Enable MMU features
config KERNEL_VM_BASE
hex "Base virtual address to link the kernel"
default 0x0
depends on MMU
help
Define the base virtual memory address for the core kernel.
The kernel expects a mappings for all physical RAM regions starting at
this virtual address, with any unused space up to the size denoted by
KERNEL_VM_SIZE available for memory mappings. This base address denotes
the start of the RAM mapping and may not be the base address of the
kernel itself, but the offset of the kernel here will be the same as the
offset from the beginning of physical memory where it was loaded.
If there are multiple physical RAM regions which are discontinuous in
the physical memory map, they should all be mapped in a continuous
virtual region, with bounds defined by KERNEL_RAM_SIZE.
By default, this is the same as the DT_CHOSEN_Z_SRAM physical base SRAM
address from DTS, in which case RAM will be identity-mapped. Some
architectures may require RAM to be mapped in this way; they may have
just one RAM region and doing this makes linking much simpler, as
at least when the kernel boots all virtual RAM addresses are the same
as their physical address (demand paging at runtime may later modify
this for some subset of non-pinned pages).
Otherwise, if RAM isn't identity-mapped:
1. It is the architecture's responsibility to transition the
instruction pointer to virtual addresses at early boot before
entering the kernel at z_cstart().
2. The underlying architecture may impose constraints on the bounds of
the kernel's address space, such as not overlapping physical RAM
regions if RAM is not identity-mapped, or the virtual and physical
base addresses being aligned to some common value (which allows
double-linking of paging structures to make the instruction pointer
transition simpler).
(The ‘depends on’ condition includes propagated dependencies from ifs and menus.)