Linux 内核模块
Linux 内核模块是一个形如 hello.ko 的文件：
root@ecs-3c5a:~/_linux/module# file hello.ko
hello.ko: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), BuildID[sha1]=7ebda760c804b79dd35c03a74ca02d727c904dbc, with debug_info, not stripped
通过 insmod 和 rmmod 可以加载和卸载模块：
root@ecs-3c5a:~/_linux/module# sudo insmod hello.ko root@ecs-3c5a:~/_linux/module# sudo rmmod hello
通过 lsmod 可以查看当前系统加载的全部模块：
root@ecs-3c5a:~/_linux/module# lsmod
Module Size Used by
hello 12288 0
tls 155648 0
qrtr 53248 2
intel_rapl_msr 20480 0
intel_rapl_common 40960 1 intel_rapl_msr
intel_uncore_frequency_common 16384 0
skx_edac_common 24576 0
nfit 81920 1 skx_edac_common
rapl 20480 0
i2c_piix4 32768 0
joydev 32768 0
input_leds 12288 0
mac_hid 12288 0
serio_raw 20480 0
binfmt_misc 24576 1
sch_fq_codel 24576 3
dm_multipath 45056 0
msr 12288 0
efi_pstore 12288 0
nfnetlink 20480 1
dmi_sysfs 24576 0
qemu_fw_cfg 24576 0
ip_tables 32768 0
x_tables 65536 1 ip_tables
autofs4 57344 2
btrfs 2039808 0
blake2b_generic 24576 0
raid10 73728 0
raid456 196608 0
async_raid6_recov 20480 1 raid456
async_memcpy 16384 2 raid456,async_raid6_recov
async_pq 20480 2 raid456,async_raid6_recov
async_xor 16384 3 async_pq,raid456,async_raid6_recov
async_tx 16384 5 async_pq,async_memcpy,async_xor,raid456,async_raid6_recov
xor 20480 2 async_xor,btrfs
raid6_pq 126976 4 async_pq,btrfs,raid456,async_raid6_recov
libcrc32c 12288 2 btrfs,raid456
raid1 57344 0
raid0 24576 0
hid_generic 12288 0
usbhid 77824 0
hid 180224 2 usbhid,hid_generic
crct10dif_pclmul 12288 1
crc32_pclmul 12288 0
polyval_clmulni 12288 0
polyval_generic 12288 1 polyval_clmulni
ghash_clmulni_intel 16384 0
sha256_ssse3 32768 1
sha1_ssse3 32768 0
psmouse 217088 0
pata_acpi 12288 0
cirrus 20480 0
floppy 131072 0
aesni_intel 356352 0
crypto_simd 16384 1 aesni_intel
cryptd 24576 2 crypto_simd,ghash_clmulni_intel
通过 dmesg 可以查看内核日志：
root@ecs-3c5a:~/_linux/module# dmesg | tail
[ 444.503080] kauditd_printk_skb: 114 callbacks suppressed
[ 444.503084] audit: type=1400 audit(1763024967.936:125): apparmor="STATUS" operation="profile_replace" info="same as current profile, skipping" profile="unconfined" name="/usr/lib/snapd/snap-confine" pid=2688 comm="apparmor_parser"
[ 444.503853] audit: type=1400 audit(1763024967.937:126): apparmor="STATUS" operation="profile_replace" info="same as current profile, skipping" profile="unconfined" name="/usr/lib/snapd/snap-confine//mount-namespace-capture-helper" pid=2688 comm="apparmor_parser"
[ 762.902684] hello: loading out-of-tree module taints kernel.
[ 762.902691] hello: module license 'MIT' taints kernel.
[ 762.902693] Disabling lock debugging due to kernel taint
[ 762.902695] hello: module verification failed: signature and/or required key missing - tainting kernel
[ 762.902696] hello: module license taints kernel.
[ 762.902973] Hello, Ubuntu kernel module!
[ 804.385241] Goodbye, Ubuntu kernel module!
使用 C 语言编写一个内核模块 | 单文件
创建一个 hello.c 文件：
#include <linux/module.h>
#include <linux/init.h>
static int __init hello_init(void) {
printk(KERN_INFO "Hello, Ubuntu kernel module!\n");
return 0;
}
static void __exit hello_exit(void) {
printk(KERN_INFO "Goodbye, Ubuntu kernel module!\n");
}
module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("MIT");
MODULE_DESCRIPTION("A simple Ubuntu kernel module");
MODULE_AUTHOR("AzurIce");
Kbuild
Kbuild 的本质其实就是 Makefile 脚本，被 Makefile include。它基于一些约定的变量和规则使 Linux 的 Makefile 编写更加方便。
在 Kbuild 中 obj-m 表示要被编译为独立模块的目标文件列表。
创建一个 Kbuild 文件：
obj-m += hello.o
构建与加载测试
然后使用 make -C /lib/modules/$(uname -r)/build M=<dir> modules 构建模块：
root@ecs-3c5a ~/_/module-c# make -C /lib/modules/6.8.0-59-generic/build M=/root/_linux/module-c modules
make[1]: Entering directory '/usr/src/linux-headers-6.8.0-59-generic'
warning: the compiler differs from the one used to build the kernel
The kernel was built by: x86_64-linux-gnu-gcc-13 (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
You are using: gcc-13 (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
CC [M] /root/_linux/module-c/hello.o
MODPOST /root/_linux/module-c/Module.symvers
CC [M] /root/_linux/module-c/hello.mod.o
LD [M] /root/_linux/module-c/hello.ko
BTF [M] /root/_linux/module-c/hello.ko
Skipping BTF generation for /root/_linux/module-c/hello.ko due to unavailability of vmlinux
make[1]: Leaving directory '/usr/src/linux-headers-6.8.0-59-generic'
构建完成后即得到一个 hello.ko 文件。
然后可以加载、卸载、查看日志：
root@ecs-3c5a ~/_/module-c# insmod hello_module.ko
root@ecs-3c5a ~/_/module-c# rmmod hello_module.ko
root@ecs-3c5a ~/_/module-c# dmesg | tail -2
[ 592.588753] Hello, Ubuntu kernel module!
[ 600.088256] Goodbye, Ubuntu kernel module!
使用 C 语言编写一个内核模块 | 多文件
#include <linux/module.h>
MODULE_LICENSE("MIT");
MODULE_DESCRIPTION("A simple Ubuntu kernel module");
MODULE_AUTHOR("AzurIce");
#include <linux/module.h>
#include <linux/init.h>
static int __init hello_init(void) {
printk(KERN_INFO "Hello, Ubuntu kernel module!\n");
return 0;
}
module_init(hello_init)
#include <linux/module.h>
#include <linux/init.h>
static void __exit hello_exit(void) {
printk(KERN_INFO "Goodbye, Ubuntu kernel module!\n");
}
module_exit(hello_exit);
Kbuild
使用 <name>-objs 来声明 <name>.o 的依赖。
obj-m += module.o
module-objs := hello.o hello_init.o hello_exit.o
使用 Rust 编写一个内核模块
Rust-for-Linux/rust-out-of-tree-module。
用于 linux 6.8 的 commit hash：e36fc14c01e3293b5e4302b57ba18f2e90b6bd22
需要额外安装 linux-lib-rust-$(uname -r) 包
在 Ubuntu 上需要使用 apt install 来安装 rustc，不能使用 rustup（即便都是 1.75.0）
error[E0514]: found crate `core` compiled by an incompatible version of rustc
|
= note: the following crate versions were found:
crate `core` compiled by rustc 1.75.0 (82e1608df 2023-12-21) (built from a source tarball): /usr/src/linux-lib-rust-6.8.0-59-generic/rust/libcore.rmeta
= help: please recompile that crate using this compiler (rustc 1.75.0 (82e1608df 2023-12-21)) (consider running `cargo clean` first)
构建与加载测试
root@ecs-3c5a ~/_/module-rust ((e36fc14c))# make
make -C /lib/modules/`uname -r`/build M=$PWD
make[1]: Entering directory '/usr/src/linux-headers-6.8.0-59-generic'
warning: the compiler differs from the one used to build the kernel
The kernel was built by: x86_64-linux-gnu-gcc-13 (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
You are using: gcc-13 (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
RUSTC [M] /root/_linux/module-rust/rust_out_of_tree.o
MODPOST /root/_linux/module-rust/Module.symvers
CC [M] /root/_linux/module-rust/rust_out_of_tree.mod.o
LD [M] /root/_linux/module-rust/rust_out_of_tree.ko
BTF [M] /root/_linux/module-rust/rust_out_of_tree.ko
Skipping BTF generation for /root/_linux/module-rust/rust_out_of_tree.ko due to unavailability of vmlinux
make[1]: Leaving directory '/usr/src/linux-headers-6.8.0-59-generic'
root@ecs-3c5a ~/_/module-rust ((e36fc14c))# insmod rust_out_of_tree.ko
root@ecs-3c5a ~/_/module-rust ((e36fc14c))# rmmod rust_out_of_tree
root@ecs-3c5a ~/_/module-rust ((e36fc14c))# dmesg | tail -3
[ 6784.132227] rust_out_of_tree: Rust out-of-tree sample (init)
[ 6786.113010] rust_out_of_tree: My numbers are [72, 108, 200]
[ 6786.113019] rust_out_of_tree: Rust out-of-tree sample (exit)