f356261b67
Since UEFI requires app to be run in physical address space, we allocate memory that are identity mapped. Previous identity mapping works as follows: 1. call vmm_alloc_contigious to obtain a VA1(virtual address) mapping to PA1(physical address) 2. Use arch_mmu_query to obtain PA1 from VA1 3. arch_mmu_unmap VA1 <-> PA1 4. arch_mmu_map PA1 <-> PA1 Now we can return PA1 as a valid virtual address pointer, which is mapped to physical memory. However, this has problems. LK allocates a vmm_region_t struct for each call to vmm_alloc_* . This struct can never be free'ed, as the associated virtual address VA1 is forever lost. We can't even free PA1, as PA1 is not a valid argument to vmm_free(PA1 does not have associated vmm_region_t struct). The new approach uses pmm_alloc and vmm_reserve_space, allowing vmm_free_region to be called.
The Little Kernel Embedded Operating System
The LK kernel is an SMP-aware kernel designed for small systems ported to a variety of platforms and cpu architectures.
See https://github.com/littlekernel/lk for the latest version.
High Level Features
- Fully-reentrant multi-threaded preemptive kernel
- Portable to many 32 and 64 bit architectures
- Support for wide variety of embedded and larger platforms
- Powerful modular build system
- Large number of utility components selectable at build time
Supported architectures
- ARM32
- Cortex-M class cores (armv6m - armv8m)
- ARMv7+ Cortex-A class cores
- ARM64
- ARMv8 and ARMv9 cores
- RISC-V 32 and 64bit bit in machine and supervisor mode
- x86-32 and x86-64
- Motorola 68000
- Microblaze
- MIPS
- OpenRISC 1000
- VAX (experimental)
TODO
To build and test for ARM64 on linux
- install or build qemu. v2.4 and above is recommended.
- install gcc for arm64 (see note 1)
- run scripts/do-qemuarm -6 (from the lk directory)
- you should see 'welcome to lk/MP'
This will get you a interactive prompt into LK which is running in qemu arm64 machine 'virt' emulation. type 'help' for commands.
Note: for ubuntu x86-64 sudo apt-get install gcc-aarch64-linux-gnu or fetch a prebuilt toolchain from https://newos.org/toolchains/aarch64-elf-14.1.0-Linux-x86_64.tar.xz
Building with LLVM-based toolchains
To build LK with a LLVM-based toolchain you will have to manually specify the compiler and linker in the environemnt.
Unlike GCC clang is a cross-compiler by default, so the target needs to be specified as part of the CC/CXX/CPP variables.
For example, assuming LLVM is in /opt/llvm/bin/, the following command will work to build for 64-bit RISC-V:
gmake qemu-virt-riscv64-test 'CC=/opt/llvm/bin/clang --target=riscv64-unknown-elf' 'CPP=/opt/llvm/bin/clang-cpp --target=riscv64-unknown-elf' 'CXX=/opt/llvm/bin/clang++ --target=riscv64-unknown-elf' 'LD=/opt/llvm/bin/ld.lld' TOOLCHAIN_PREFIX=/opt/llvm/bin/llvm- CPPFILT=/opt/llvm/bin/llvm-cxxfilt
TOOLCHAIN_PREFIX can be set to use the LLVM binutils, but due to the different naming of llvm-cxxfilt vs c++filt it needs to be set explicitly.
To build for AArch64 the command looks similar, just with a different --target= flag.
gmake qemu-virt-arm64-test 'CC=/opt/llvm/bin/clang --target=aarch64-unknown-elf' 'CPP=/opt/llvm/bin/clang-cpp --target=aarch64-unknown-elf' 'CXX=/opt/llvm/bin/clang++ --target=aarch64-unknown-elf' 'LD=/opt/llvm/bin/ld.lld' TOOLCHAIN_PREFIX=/opt/llvm/bin/llvm- CPPFILT=/opt/llvm/bin/llvm-cxxfilt