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43-kfuncs/module/.gitignore

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+# Ignore object files and kernel modules
+*.o
+*.ko
+*.mod
+*.mod.c
+*.symvers
+*.order
+
+# Ignore temporary and backup files
+*~
+*.bak
+*.tmp
+*.swp
+
+# Ignore build directory if generated
+/Module.symvers
+/Modules.markers
+/Module.markers
+/modules.order
+
+# Ignore other automatically generated files
+*.cmd
+.tmp_versions/

43-kfuncs/module/Makefile

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+obj-m += hello.o  # hello.o is the target
+
+# Enable BTF generation
+KBUILD_CFLAGS += -g -O2
+
+all:
+	# Compile the module with BTF information
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

43-kfuncs/module/compact.h

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+// Compatible for lower kernel versions. No need in 6.11.
+#ifndef BTF_SET8_KFUNCS
+/* This flag implies BTF_SET8 holds kfunc(s) */
+#define BTF_SET8_KFUNCS		(1 << 0)
+#endif
+#ifndef BTF_KFUNCS_START
+#define BTF_KFUNCS_START(name) static struct btf_id_set8 __maybe_unused name = { .flags = BTF_SET8_KFUNCS };
+#endif
+#ifndef BTF_KFUNCS_END
+#define BTF_KFUNCS_END(name)
+#endif

43-kfuncs/module/hello.c

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+#include <linux/init.h>    // Macros for module initialization
+#include <linux/module.h>  // Core header for loading modules
+#include <linux/kernel.h>  // Kernel logging macros
+#include <linux/bpf.h>
+#include <linux/btf.h>
+#include <linux/btf_ids.h>
+
+__bpf_kfunc u64 bpf_kfunc_call_test(u32 a, u64 b, u32 c, u64 d);
+
+/* Define a kfunc function */
+__bpf_kfunc_start_defs();
+
+__bpf_kfunc u64 bpf_kfunc_call_test(u32 a, u64 b, u32 c, u64 d)
+{
+	return a + b + c + d;
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(bpf_kfunc_example_ids_set)
+BTF_ID_FLAGS(func, bpf_kfunc_call_test)
+BTF_KFUNCS_END(bpf_kfunc_example_ids_set)
+
+// Register the kfunc ID set
+static const struct btf_kfunc_id_set bpf_kfunc_example_set = {
+    .owner = THIS_MODULE,
+    .set = &bpf_kfunc_example_ids_set,
+};
+
+// Function executed when the module is loaded
+static int __init hello_init(void)
+{
+    int ret;
+
+    printk(KERN_INFO "Hello, world!\n");
+    // Register the BTF kfunc ID set
+    ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_KPROBE, &bpf_kfunc_example_set);
+    if (ret) {
+        pr_err("bpf_kfunc_example: Failed to register BTF kfunc ID set\n");
+        return ret;
+    }
+    printk(KERN_INFO "bpf_kfunc_example: Module loaded successfully\n");
+    return 0;  // Return 0 if successful
+}
+
+// Function executed when the module is removed
+static void __exit hello_exit(void)
+{
+    // Unregister the BTF kfunc ID set
+    // unregister_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC, &bpf_kfunc_example_set);
+    printk(KERN_INFO "Goodbye, world!\n");
+}
+
+// Macros to define the module’s init and exit points
+module_init(hello_init);
+module_exit(hello_exit);
+
+MODULE_LICENSE("GPL");               // License type (GPL)
+MODULE_AUTHOR("Your Name");          // Module author
+MODULE_DESCRIPTION("A simple module"); // Module description
+MODULE_VERSION("1.0");               // Module version