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Asked: 2026-05-16T07:19:23+00:00

If two kernel module contain EXPORT_SYMBOL(a), a is defined as: int a, what will

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If two kernel module contain EXPORT_SYMBOL(a), a is defined as: int a, what will happen if two module was inserted? which “a” will be used?

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  1. Editorial Team

    You can’t insert duplicate symbols into the kernel. Example:

    The xor module loaded in my kernel

    nwatkins@kyoto:~$ lsmod | grep xor
xor                     4685  1 async_xor

    The exported xor_blocks symbol in the xor module

    nwatkins@kyoto:~$ nm /lib/modules/2.6.32-24-generic/kernel/crypto/xor.ko  | grep xor_blocks
0000000000000000 r __kcrctab_xor_blocks
0000000000000000 r __kstrtab_xor_blocks
0000000000000000 r __ksymtab_xor_blocks
0000000000000bb0 T xor_blocks

    Another exported xor_blocks symbol in a module I created

    nwatkins@kyoto:~$ nm mod-t1.ko  | grep xor
0000000000000000 r __kcrctab_xor_blocks
0000000000000000 r __kstrtab_xor_blocks
0000000000000000 r __ksymtab_xor_blocks
0000000000000000 T xor_blocks

    Error reported from insmod

    nwatkins@kyoto:~$ sudo insmod mod-t1.ko 
insmod: error inserting 'mod-t1.ko': -1 Invalid module format

    Duplicate error message from dmesg

    [422002.174033] mod_t1: exports duplicate symbol xor_blocks (owned by xor)
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