On Tue, Jan 14, 2014 at 6:38 PM, Le Tan [off-list ref] wrote:

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!

How you are specifying kvm module to use symbol which is exported by some

other module?

After compiling your logger module, it must have generated a Module.symvers
file containing symbols exported by your module,
Please try with adding following in kvm module make file and compile again:

*KBUILD_EXTRA_SYMBOLS+= <Your logger module>/Module.symvers *


2014/1/14 Chetan Nanda [off-list ref]

quoted

On Tue, Jan 14, 2014 at 12:38 PM, Le Tan [off-list ref] wrote:

quoted

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,

quoted

quoted

2014/1/14 Henrique Rodrigues [off-list ref]

quoted

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 [off-list ref] wrote:

quoted

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!

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