<div dir="ltr"><div>You are getting a compile error because the symbol you are trying to export is not complete.<br></div><div><br></div>Step back and think about what you are trying to do. You were initially trying to export (with EXPORT_SYMBOL) a function that is supposed to be implemented by your module, but you state that its implementation in another object file that will be linked later (with the keyword "extern"). You don't provide that implementation, and that is the reason why your compilation fails.<div>
<br><div>With a function pointer, however, you are exporting a complete object, that is a pointer to a function with a certain signature. </div><div><br></div><div>This might be confusing at first, specially if you don't know how compilers work, but I hope this helps.</div>
<div><br></div><div>--</div><div>Henrique Rodrigues</div><div><a href="http://www.dcc.ufmg.br/~hsr">http://www.dcc.ufmg.br/~hsr</a></div><div><br></div><div><br></div><div><br><div><div><div><br></div><div><br></div></div>
</div></div></div></div><div class="gmail_extra"><br clear="all"><div><div dir="ltr"><div>--</div>Henrique Rodrigues<br><div><a href="http://www.dcc.ufmg.br/~hsr" target="_blank">http://www.dcc.ufmg.br/~hsr</a></div></div>
</div>
<br><br><div class="gmail_quote">On Mon, Jan 13, 2014 at 11:08 PM, Le Tan <span dir="ltr"><<a href="mailto:tamlokveer@gmail.com" target="_blank">tamlokveer@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr"><font size="4">Thanks very much! I will try that later. What you mentioned is another amazing sight. But I am confused that why it can't work if I export a function from my module and call it in the kvm? Do I have to modify the makefile of kvm? How? I have referenced to the doc of KBuild. It said that :</font><div>
<div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
Sometimes, an external module uses exported symbols from</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
another external module. kbuild needs to have full knowledge of</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
all symbols to avoid spliitting out warnings about undefined</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
symbols. <font color="#ff0000">Three solutions exist for this situation.</font></div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
NOTE: The method with a top-level kbuild file is recommended</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
but may be impractical in certain situations.</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
<font color="#ff0000">Use a top-level kbuild file</font></div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
If you have two modules, foo.ko and bar.ko, where</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
foo.ko needs symbols from bar.ko, you can use a</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
common top-level kbuild file so both modules are</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
compiled in the same build. Consider the following</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
directory layout:</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
./foo/ <= contains foo.ko</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
./bar/ <= contains bar.ko</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
The top-level kbuild file would then look like:</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
#./Kbuild (or ./Makefile):</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
obj-y := foo/ bar/</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
And executing</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
$ make -C $KDIR M=$PWD</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
will then do the expected and compile both modules with</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
full knowledge of symbols from either module.</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
<font color="#ff0000"> Use an extra Module.symvers file</font></div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
When an external module is built, a Module.symvers file</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
is generated containing all exported symbols which are</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
not defined in the kernel. To get access to symbols</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
from bar.ko, copy the Module.symvers file from the</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
compilation of bar.ko to the directory where foo.ko is</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
built. During the module build, kbuild will read the</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
Module.symvers file in the directory of the external</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
module, and when the build is finished, a new</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
Module.symvers file is created containing the sum of</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
all symbols defined and not part of the kernel.</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
<font color="#ff0000"> Use "make" variable KBUILD_EXTRA_SYMBOLS</font></div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
If it is impractical to copy Module.symvers from</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
another module, you can assign a space separated list</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
of files to KBUILD_EXTRA_SYMBOLS in your build file.</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
These files will be loaded by modpost during the</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
initialization of its symbol tables.</div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
<span style="font-size:large;font-family:arial;line-height:normal;color:rgb(34,34,34)"><br></span></div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
<span style="font-size:large;font-family:arial;line-height:normal;color:rgb(34,34,34)">But I have tried those methods. They don't work. Why?</span></div></div><div style="line-height:20px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
<font size="4">Thanks for your help very much!</font></div><div style="line-height:20px;font-size:14.285715103149414px;font-family:'Microsoft YaHei UI','Microsoft YaHei',SimSun,'Segoe UI',Tahoma,Helvetica,sans-serif,'Microsoft YaHei',Georgia,Helvetica,Arial,sans-serif,宋体,PMingLiU,serif">
<br></div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><br><div class="gmail_quote">2014/1/14 Henrique Rodrigues <span dir="ltr"><<a href="mailto:henriquesilvar@gmail.com" target="_blank">henriquesilvar@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi Le,<div><br></div><div>You can do that by exporting a function pointer from the kvm code that is only called if it is not null. Then, when you load your module, you set that exported function pointer (I'm assuming that you want to call your module's function from the kvm code... ). Here is a post on how to do that:</div>
<div><br></div><div><a href="http://stackoverflow.com/questions/11463184/how-to-use-exported-symbols-in-the-linux-kernel" target="_blank">http://stackoverflow.com/questions/11463184/how-to-use-exported-symbols-in-the-linux-kernel</a><br>
</div><div><a href="http://stackoverflow.com/questions/1196944/can-i-replace-a-linux-kernel-function-with-a-module" target="_blank">http://stackoverflow.com/questions/1196944/can-i-replace-a-linux-kernel-function-with-a-module</a><br>
</div>
<div><div><br></div><div>Best,</div></div><div class="gmail_extra"><div><div dir="ltr"><div>--</div>Henrique Rodrigues<br><div><a href="http://www.dcc.ufmg.br/~hsr" target="_blank">http://www.dcc.ufmg.br/~hsr</a></div></div>
</div>
<br><br><div class="gmail_quote"><div><div>On Mon, Jan 13, 2014 at 2:47 AM, Le Tan <span dir="ltr"><<a href="mailto:tamlokveer@gmail.com" target="_blank">tamlokveer@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div><div><div dir="ltr">Hello! I am writing a device driver module. I define some functions in the module, for example print_record(). I am doing something in the kvm, so I want to call print_record() in the file of kvm module, for example, I may call print_record() in file /arch/x86/kvm/x86.c to put something into my device driver module.<div>
Now comes the question.</div><div>1. Where should I put the codes of my device driver module? It's the first time I write the device driver.</div><div>2. After compiling my module, I encounter an error when I compile the kvm module.</div>
<div> ERROR: "print_record" [arch/x86/kvm/kvm.ko] undefined!</div><div> I use EXPORT_SYMBOL(print_record) in my module file. I use "extern" to declare print_record() and then call print_record() in file x86.c. </div>
<div> To solve this problem, I have tried to copy the Module.symvers from my module folder to /arch/x86/kvm/. But it doesn't work. I have also tried to add <strong style="vertical-align:baseline;line-height:18px;font-size:14px;font-family:Arial,'Liberation Sans','DejaVu Sans',sans-serif;margin:0px;border:0px;padding:0px">KBUILD_EXTRA_SYMBOLS </strong>to the Makefile of kvm. It doesn't work either.</div>
<div> I cat /proc/kallsyms and find that the type of symbol "print_record" is "t" ( local text). What should I do? How to call functions defined in my own module from kvm? Maybe there is something wrong in Makefiles?</div>
<div><br></div><div>Any suggestion is appreciated!</div><div>Thanks!</div></div>
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