我必须在内核中打印mem_mapvariables的内容。
但是，当我通过发布make编译我的代码时，我发现：
WARNING: "mem_map" [/home/babak/code/module/mem_map.ko] undefined! 从：
make -C /home/babak/code/linux-3.19.5 M=/home/babak/code/module modules make[1]: Entering directory '/home/babak/code/linux-3.19.5' CC [M] /home/babak/code/module/mem_map.o Building modules, stage 2. MODPOST 1 modules WARNING: "mem_map" [/home/babak/code/module/mem_map.ko] undefined! LD [M] /home/babak/code/module/mem_map.ko make[1]: Leaving directory '/home/babak/code/linux-3.19.5'
有我包括头，我的理解是，mem_map应该是在mmzone.h我不知道为什么它不拾起variables。
#include <linux/module.h> #include <linux/init.h> #include <linux/kernel.h> #include <linux/types.h> /* size_t */ #include <linux/fcntl.h> /* O_ACCMODE */ #include <asm/switch_to.h> #include <asm/uaccess.h> /* copy_from/to_user */ #include <linux/fs.h> // for basic filesystem #include <linux/proc_fs.h> // for the proc filesystem #include <linux/seq_file.h> // for sequence files #include <linux/mmzone.h> MODULE_LICENSE("Dual BSD/GPL"); static struct proc_dir_entry* proc_file; /* memory map functions */ int mem_map_show(struct seq_file *m, void *v); //virtual_to_physical inline unsigned long virt_to_phy(unsigned long addr); inline unsigned long virt_to_phy(unsigned long addr){ return __pa(addr); } int mem_map_show(struct seq_file *m, void *v){ int ret_val = 0; printk(KERN_INFO "Proc file read \n"); ret_val = seq_printf(m, "mem_map virt addr: %p \n", mem_map); ret_val += seq_printf(m, "mem_map phys addr: %lu \n",virt_to_phy((unsigned long)mem_map)); ret_val += seq_printf(m, "mem_map phys pages: %lu \n", (long unsigned int)get_num_physpages); return ret_val; } static int mem_map_open(struct inode *inode, struct file *file){ return single_open(file, mem_map_show, NULL); } struct file_operations mem_map_fops = { .owner = THIS_MODULE, .open = mem_map_open, .read = seq_read, .llseek = seq_lseek, .release = single_release, }; static int __init mem_map_init(void){ printk(KERN_INFO "Loaded mem_map module\n"); proc_file = proc_create("mem_map", 0, NULL, &mem_map_fops); if(!proc_file){ printk(KERN_ALERT "Error: Could not initialize /proc/mem_map"); return -ENOMEM; } return 0; } static void __exit mem_map_exit(void){ remove_proc_entry("mem_map",NULL); printk(KERN_INFO "Proc file unloaded \n"); } /* Declaration of the init and exit functions */ module_init(mem_map_init); module_exit(mem_map_exit);
在链接器阶段警告像
WARNING: "mem_map" [/home/babak/code/module/mem_map.ko] undefined!
意味着mem_map被声明，但是它的定义不能被模块访问。
因此，您需要在源文件（ .c文件）中使用像EXPORT_SYMBOL(mem_map)或EXPORT_SYMBOL_GPL(mem_map)这样的搜索语句。
发现对于内核3.19（ mm/memory.c ）：
#ifndef CONFIG_NEED_MULTIPLE_NODES /* use the per-pgdat data instead for discontigmem - mbligh */ unsigned long max_mapnr; struct page *mem_map; EXPORT_SYMBOL(max_mapnr); EXPORT_SYMBOL(mem_map); #endif
可能没有CONFIG_NEED_MULTIPLE_NODES内核的配置集，所以不会导出符号mem_map （甚至没有定义）。