使用llvm 编译最新的linux 内核(LoongArch)

1. 准备交叉工具链

llvm 使用了最新的llvm-17, 编译方法见:编译LoongArch的llvm交叉工具链

gcc 从linux 官方下载：http://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/13.2.0/x86_64-gcc-13.2.0-nolibc-loongarch64-linux.tar.xz

发布llvm和gcc 相应的环境变量

$ llc --version
LLVM (http://llvm.org/):LLVM version 17.0.0rcOptimized build.Default target: x86_64-unknown-linux-gnuHost CPU: haswellRegistered Targets:aarch64     - AArch64 (little endian)aarch64_32  - AArch64 (little endian ILP32)aarch64_be  - AArch64 (big endian)amdgcn      - AMD GCN GPUsarm         - ARMarm64       - ARM64 (little endian)arm64_32    - ARM64 (little endian ILP32)armeb       - ARM (big endian)avr         - Atmel AVR Microcontrollerbpf         - BPF (host endian)bpfeb       - BPF (big endian)bpfel       - BPF (little endian)hexagon     - Hexagonlanai       - Lanailoongarch32 - 32-bit LoongArchloongarch64 - 64-bit LoongArchmips        - MIPS (32-bit big endian)mips64      - MIPS (64-bit big endian)mips64el    - MIPS (64-bit little endian)mipsel      - MIPS (32-bit little endian)msp430      - MSP430 [experimental]nvptx       - NVIDIA PTX 32-bitnvptx64     - NVIDIA PTX 64-bitppc32       - PowerPC 32ppc32le     - PowerPC 32 LEppc64       - PowerPC 64ppc64le     - PowerPC 64 LEr600        - AMD GPUs HD2XXX-HD6XXXriscv32     - 32-bit RISC-Vriscv64     - 64-bit RISC-Vsparc       - Sparcsparcel     - Sparc LEsparcv9     - Sparc V9systemz     - SystemZthumb       - Thumbthumbeb     - Thumb (big endian)ve          - VEwasm32      - WebAssembly 32-bitwasm64      - WebAssembly 64-bitx86         - 32-bit X86: Pentium-Pro and abovex86-64      - 64-bit X86: EM64T and AMD64xcore       - XCore

2. 下载内核源码

从https://www.kernel.org/ 下载最新的版本(linux-next) ，本次用的是linux 6.6rc1

3. 编译内核

$ cd linux-next
$ export ARCH=loongarch$ make O=./build_llvm LLVM=1 loongson3_defconfig
$ make O=./build_llvm LLVM=1 -j4
make[1]: 进入目录“/home/loongson/work/oh/kernel/linux-next-next-20230906/build_llvm”GEN     MakefileCALL    ../scripts/checksyscalls.shAS      arch/loongarch/kernel/genex.o
<instantiation>:11:9: error: Cannot represent a difference across sections.dword 768b-766b^
<instantiation>:11:9: error: Cannot represent a difference across sections                                                              .dword 768b-766b^
<instantiation>:11:9: error: Cannot represent a difference across sections                                                              .dword 768b-766b^
<instantiation>:11:9: error: Cannot represent a difference across sections

出现上面的错误是因为不relocalable 特性，修改内核配置关掉CONFIG_RELOCATABLE

CONFIG_CRASH_DUMP=n
CONFIG_RELOCATABLE=n

$ make O=./build_llvm LLVM=1 -j4../arch/loongarch/include/asm/percpu.h:20:4: error: compiler support for the model attribute is necessary when a recent assembler is used20 | #  error compiler support for the model attribute is necessary when a recent assembler is used|    ^

出现上面的错误是因为不module 也还不支持，修改内核配置关掉CONFIG_MODULES