On Sun, Aug 29, 2021 at 11:00 PM Bryan Brattlof [off-list ref] wrote:

On this day, August 29, 2021, thus sayeth Krish Jain:

quoted

Keeping you updated. Small win. The "Symbol version dump
"Module.symvers" is missing. " error disappeared. Now I still don't
know why

Whoop! Any win, no matter their size, always feel great. I ran around
the house yesterday after cross compiling DOOM! for an armel chip. It's
that "win" feeling you get that keeps me involved.

It is important that you find out why though. What is the importance to
having Module.symvers? and why is it a WARNING and not an ERROR?

 When a module is loaded/used, the values contained in the kernel are
compared with similar values in the module; if they are not equal, the
kernel refuses to load the module. I don't need it in my case.

What would happen if we didn't have the proper symbols when compiling or
installing this driver?
How and what generates the Module.symvers file when we *do* need it?

The kernel would refuse to load the module.

How can we turn this warning off when we don't need it?

This is covered in chapter "6. Module Versioning"

  https://www.kernel.org/doc/html/latest/kbuild/modules.html

quoted

ERROR: Kernel configuration is invalid."; \
echo >&2 "         include/generated/autoconf.h or
include/config/auto.conf are missing.";\
echo >&2 "         Run 'make oldconfig && make prepare' on kernel src
to fix it."; \


is still present.

How can I fix this?

Are there any other 'make *config' options we could try?

Yes, like main menuconfig. I tried it but it still doesn't work.

What does 'make prepare' even do?

Prepares for different architectures etc.

Why do we even need a configuration file?

  https://www.kernel.org/doc/html/latest/kbuild/kconfig.html

quoted

Best Regards

On Sun, Aug 29, 2021 at 8:28 PM Krish Jain [off-list ref] wrote:

quoted

Basically it says "you must have a prebuilt kernel available that
contains the configuration and header files used in the build." Since
for the staging kernel  "make oldconfig" asked me for  more
configurations apart from my old configuration file (as it reads the
existing .config file that was used for an old kernel and prompts the
user for options in the current kernel source that are not found in
the file) . So I *don't* currently have a prebuilt kernel that
contains all the configuration in my staging kernel's .config file. So
do I have to build the kernel once before I can just build the module
with "make CCFLAGS=-Werror W=1 M=drivers/staging/android" ?

What do all these other configuration settings turn on and off anyway?

Do we really need CONFIG_INFINIBAND turned on if we're working in the
drivers/staging tree of the kernel?

No, we don't. I removed it.

What would we gain from having a compiled kernel if we want to test a
single staging driver?

No need to compile the entire kernel I guess for my use case. But
after all this reading :( I still don't get why " sudo make
CCFLAGS=-Werror W=1 M=drivers/staging/android/  V=1" worked for you
but not for me. I still get the following errors


test -e include/generated/autoconf.h -a -e include/config/auto.conf || ( \
echo >&2; \
echo >&2 "  ERROR: Kernel configuration is invalid."; \
echo >&2 "         include/generated/autoconf.h or
include/config/auto.conf are missing.";\
echo >&2 "         Run 'make oldconfig && make prepare' on kernel src
to fix it."; \
echo >&2 ; \
/bin/false)
.....


How can I fix this?

If you found what Module.symvers does, you should know this.

quoted

quoted

quoted

quoted

Again, do not allow others to rob you of learning how to solve these
issues yourself. I *strongly* encourage you to familiarize yourself with
the Kernel Build System in the Documentation.

  https://www.kernel.org/doc/html/latest/kbuild/modules.html

Specifically the first paragraph of "2. How to Build External Modules"

It may seem like a lot for such a simple issue but it *is* worth it.
~Bryan

That section says


"To build external modules, *you must have a prebuilt kernel
available* that contains the configuration and header files used in
the build. Also, the kernel must have been built with modules enabled.
If you are using a distribution kernel, there will be a package for
the kernel you are running provided by your distribution.

An alternative is to use the “make” target “modules_prepare.” This
will make sure the kernel contains the information required. The
target exists solely as a simple way to prepare a kernel source tree
for building external modules.

NOTE: “modules_prepare” will not build Module.symvers even if
CONFIG_MODVERSIONS is set; therefore, *a full kernel build needs to be
executed to make module versioning work.*"

So I am just trying to confirm with you whether I have to first build
the kernel with like "make" or not? As you can imagine my hardware
takes *very* long to build a kernel as I did in my last attempt so I
am asking whether it is needed. Hope you understand.

I understand. Though I still don't wish to rob you of this opportunity.

Your ability to come up with these questions and answer them yourself is
what will make you a better programmer and developer.

Don't get me wrong. Greg knows all too well the garbage I can shovel his
way. It's not about knowing the answer. It about knowing how to find the
answer yourself.

~Bryan