[kernel]which the file define the variable of "phys_base"?

[lx]

hi all:
      the codes is:
#########################################
#include <linux/module.h>               // for printk()
#include <linux/mm.h>             // for struct page
#include <asm/page.h>             // for struct page
#include <asm/pgtable.h>                // for ZERO_PAGE

static int __init init_hello( void )
{
        int i;
        struct page * zero_page;
        printk( "\n   Kello, the first! \n\n" );
        i = 0x100;
        zero_page = ZERO_PAGE(&i);
        printk(" the ZERO address is %p", zero_page);
        return  0;
}

static void __exit exit_hello( void )
{
        printk( "\n   Goodbye now... \n\n" );
}

MODULE_LICENSE("GPL");
module_init(init_hello);
module_exit(exit_hello);
#########################################

I complier it. by:
#########################################
make -C /lib/modules/`uname -r`/build M=`pwd`
#########################################

the results is:
#########################################
[root at localhost kernel_test]# make -C /lib/modules/`uname -r`/build M=`pwd`
make: Entering directory `/usr/src/kernels/2.6.18-308.el5-x86_64'
  CC [M]  /opt/lx/kernel/kernel_test/zero.o
  Building modules, stage 2.
  MODPOST
*WARNING: "phys_base" [/opt/lx/kernel/kernel_test/zero.ko] undefined!*
  LD [M]  /opt/lx/kernel/kernel_test/zero.ko
make: Leaving directory `/usr/src/kernels/2.6.18-308.el5-x86_64'
#########################################

I try to find the file which defined the "phys_base", for examples;
phys_baseDefined as a variable in:

   - arch/sparc/mm/init.c, line
40<http://lxr.oss.org.cn/source/arch/sparc/mm/init.c?v=2.6.8#L40>
   - arch/sparc64/kernel/sparc64_ksyms.c, line
110<http://lxr.oss.org.cn/source/arch/sparc64/kernel/sparc64_ksyms.c?v=2.6.8#L110>
   - arch/sparc64/mm/init.c, line
47<http://lxr.oss.org.cn/source/arch/sparc64/mm/init.c?v=2.6.8#L47>
   - include/asm-sparc/page.h, line
160<http://lxr.oss.org.cn/source/include/asm-sparc/page.h?v=2.6.8#L160>
   - include/asm-sparc/pgtable.h, line
122<http://lxr.oss.org.cn/source/include/asm-sparc/pgtable.h?v=2.6.8#L122>
   - include/asm-sparc64/pgtable.h, line
227<http://lxr.oss.org.cn/source/include/asm-sparc64/pgtable.h?v=2.6.8#L227>


But I can't find the file of init.c in my computer. Please tell me some
ways to solve it, thank you.
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