About exporting symbols from an external module
Le Tan
tamlokveer at gmail.com
Tue Jan 14 08:08:01 EST 2014
Sorry, forgive me. I don't know how to reply the email like you.
My linux kernel version is 3.11, and I do not touch the kvm makefile. Now
let me show you in detail.
First I put the files of my module in " /arch/x86/logger ", "logger" is the
directory I create. The Makefile in " /arch/x86/kvm/" I think is the
Makefile of kvm. It is like this:
ccflags-y += -Ivirt/kvm -Iarch/x86/kvm
CFLAGS_x86.o := -I.
CFLAGS_svm.o := -I.
CFLAGS_vmx.o := -I.
KVM := ../../../virt/kvm
kvm-y += $(KVM)/kvm_main.o $(KVM)/ioapic.o \
$(KVM)/coalesced_mmio.o $(KVM)/irq_comm.o \
$(KVM)/eventfd.o $(KVM)/irqchip.o
kvm-$(CONFIG_KVM_DEVICE_ASSIGNMENT) += $(KVM)/assigned-dev.o $(KVM)/iommu.o
kvm-$(CONFIG_KVM_ASYNC_PF) += $(KVM)/async_pf.o
kvm-y += x86.o mmu.o emulate.o i8259.o irq.o lapic.o \
i8254.o cpuid.o pmu.o
kvm-intel-y += vmx.o
kvm-amd-y += svm.o
obj-$(CONFIG_KVM) += kvm.o
obj-$(CONFIG_KVM_INTEL) += kvm-intel.o
obj-$(CONFIG_KVM_AMD) += kvm-amd.o
And the Makefile of my module in "/arch/x86/logger" is like this:
ifneq ($(KERNELRELEASE),)
obj-m := logger.o
logger-objs := logger_main.o
else
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
modules:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
endif
clean:
rm -rf *.o *.ko *.mod.c
So I compile my module first by running "make", then insmod it. I don't
install it because I don't know if it is necessary. Then I go to the root
of my linux code, and run a shell containing "make modules". Then it will
show that :
make -j 16 modules
make[1]: Nothing to be done for `all'.
CHK include/generated/uapi/linux/version.h
make[1]: Nothing to be done for `relocs'.
CHK include/generated/utsrelease.h
CALL scripts/checksyscalls.sh
CC [M] arch/x86/kvm/x86.o
LD [M] arch/x86/kvm/kvm.o
LD [M] arch/x86/kvm/kvm-intel.o
LD [M] arch/x86/kvm/kvm-amd.o
Building modules, stage 2.
MODPOST 2832 modules
ERROR: "print_record" [arch/x86/kvm/kvm.ko] undefined!
make[1]: *** [__modpost] Error 1
make: *** [modules] Error 2
rmmod kvm_intel
rmmod kvm
cp /home/tanle/study/replay/linux-log/linux-3.11-replay/arch/x86/kvm/kvm.ko
/lib/modules/3.11.0+/kernel/arch/x86/kvm/kvm.ko
cp
/home/tanle/study/replay/linux-log/linux-3.11-replay/arch/x86/kvm/kvm-intel.ko
/lib/modules/3.11.0+/kernel/arch/x86/kvm/kvm-intel.ko
modprobe kvm
modprobe kvm_intel
Notice that I add two sentences to the /arch/x86/kvm/x86.c:
extern void print_record(char *format); //This functino is
defined in my module, this sentence is global
print_record(NULL); //Call this function in the
vcpu_enter_guest() function
So I don't know how to deal with this. I have poor knowledge about makefile
and KBuild.
Thanks for helping me again!
2014/1/14 Chetan Nanda <chetannanda at gmail.com>
>
>
>
> On Tue, Jan 14, 2014 at 12:38 PM, Le Tan <tamlokveer at gmail.com> wrote:
>
>> 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 :
>> Sometimes, an external module uses exported symbols from
>> another external module. kbuild needs to have full knowledge of
>> all symbols to avoid spliitting out warnings about undefined
>> symbols. Three solutions exist for this situation.
>>
>> NOTE: The method with a top-level kbuild file is recommended
>> but may be impractical in certain situations.
>>
>> Use a top-level kbuild file
>> If you have two modules, foo.ko and bar.ko, where
>> foo.ko needs symbols from bar.ko, you can use a
>> common top-level kbuild file so both modules are
>> compiled in the same build. Consider the following
>> directory layout:
>>
>> ./foo/ <= contains foo.ko
>> ./bar/ <= contains bar.ko
>>
>> The top-level kbuild file would then look like:
>>
>> #./Kbuild (or ./Makefile):
>> obj-y := foo/ bar/
>>
>> And executing
>>
>> $ make -C $KDIR M=$PWD
>>
>> will then do the expected and compile both modules with
>> full knowledge of symbols from either module.
>>
>> Use an extra Module.symvers file
>> When an external module is built, a Module.symvers file
>> is generated containing all exported symbols which are
>> not defined in the kernel. To get access to symbols
>> from bar.ko, copy the Module.symvers file from the
>> compilation of bar.ko to the directory where foo.ko is
>> built. During the module build, kbuild will read the
>> Module.symvers file in the directory of the external
>> module, and when the build is finished, a new
>> Module.symvers file is created containing the sum of
>> all symbols defined and not part of the kernel.
>>
>> Use "make" variable KBUILD_EXTRA_SYMBOLS
>> If it is impractical to copy Module.symvers from
>> another module, you can assign a space separated list
>> of files to KBUILD_EXTRA_SYMBOLS in your build file.
>> These files will be loaded by modpost during the
>> initialization of its symbol tables.
>>
>> But I have tried those methods. They don't work. Why?
>> Thanks for your help very much!
>>
>
> Please show your kvm module makefile,
>
>
>>
>>
>
>>
>> 2014/1/14 Henrique Rodrigues <henriquesilvar at gmail.com>
>>
>>> Hi Le,
>>>
>>> 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:
>>>
>>>
>>> http://stackoverflow.com/questions/11463184/how-to-use-exported-symbols-in-the-linux-kernel
>>>
>>> http://stackoverflow.com/questions/1196944/can-i-replace-a-linux-kernel-function-with-a-module
>>>
>>> Best,
>>> --
>>> Henrique Rodrigues
>>> http://www.dcc.ufmg.br/~hsr
>>>
>>>
>>> On Mon, Jan 13, 2014 at 2:47 AM, Le Tan <tamlokveer at gmail.com> wrote:
>>>
>>>> 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.
>>>> Now comes the question.
>>>> 1. Where should I put the codes of my device driver module? It's the
>>>> first time I write the device driver.
>>>> 2. After compiling my module, I encounter an error when I compile the
>>>> kvm module.
>>>> ERROR: "print_record" [arch/x86/kvm/kvm.ko] undefined!
>>>> 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.
>>>> 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 *KBUILD_EXTRA_SYMBOLS *to the Makefile of kvm. It doesn't work
>>>> either.
>>>> 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?
>>>>
>>>> Any suggestion is appreciated!
>>>> Thanks!
>>>>
>>>> _______________________________________________
>>>> Kernelnewbies mailing list
>>>> Kernelnewbies at kernelnewbies.org
>>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>>>
>>>>
>>>
>>
>> _______________________________________________
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>>
>
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