On Wed, Dec 11, 2024 at 12:34 AM Jon Hunter <jonathanh@xxxxxxxxxx> wrote:
>
> Hi Masahiro,
>
> On 10/11/2024 01:34, Masahiro Yamada wrote:
> > Currently, Kbuild always operates in the output directory of the kernel,
> > even when building external modules. This increases the risk of external
> > module Makefiles attempting to write to the kernel directory.
> >
> > This commit switches the working directory to the external module
> > directory, allowing the removal of the $(KBUILD_EXTMOD)/ prefix from
> > some build artifacts.
> >
> > The command for building external modules maintains backward
> > compatibility, but Makefiles that rely on working in the kernel
> > directory may break. In such cases, $(objtree) and $(srctree) should
> > be used to refer to the output and source directories of the kernel.
> >
> > The appearance of the build log will change as follows:
> >
> > [Before]
> >
> > $ make -C /path/to/my/linux M=/path/to/my/externel/module
> > make: Entering directory '/path/to/my/linux'
> > CC [M] /path/to/my/externel/module/helloworld.o
> > MODPOST /path/to/my/externel/module/Module.symvers
> > CC [M] /path/to/my/externel/module/helloworld.mod.o
> > CC [M] /path/to/my/externel/module/.module-common.o
> > LD [M] /path/to/my/externel/module/helloworld.ko
> > make: Leaving directory '/path/to/my/linux'
> >
> > [After]
> >
> > $ make -C /path/to/my/linux M=/path/to/my/externel/module
> > make: Entering directory '/path/to/my/linux'
> > make[1]: Entering directory '/path/to/my/externel/module'
> > CC [M] helloworld.o
> > MODPOST Module.symvers
> > CC [M] helloworld.mod.o
> > CC [M] .module-common.o
> > LD [M] helloworld.ko
> > make[1]: Leaving directory '/path/to/my/externel/module'
> > make: Leaving directory '/path/to/my/linux'
> >
> > Printing "Entering directory" twice is cumbersome. This will be
> > addressed later.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
>
>
> Since this change I have been observing the following build error when
> building an external module ...
>
> MODPOST Module.symvers
> ERROR: modpost: drivers/gpu/host1x/host1x: 'host1x_device_init' exported
> twice. Previous export was in drivers/gpu/host1x/host1x.ko
> ERROR: modpost: drivers/gpu/host1x/host1x: 'host1x_device_exit' exported
> twice. Previous export was in drivers/gpu/host1x/host1x.ko
>
> Now host1x is an upstream driver, but I have a local copy that using to
> stage development changes (and avoid polluting the upstream driver).
> Plus I can swap between which version I am using on a live system.
>
> What I noticed is that previously the Modules.symvers for the external
> module had the full path of the external module for the name. However,
> now the name is just the relative path and in this case
> 'drivers/gpu/host1x/host1x'. Hence, this clashes with the in-kernel
> driver and we get the 'exported twice' error.
>
> I have been looking to see if there is a way to fix this because it has
> been a useful feature to override an upstream driver with a locally
> modified version.
I do not know how to reproduce it.
if (s && (!external_module || s->module->is_vmlinux || s->module == mod)) {
is not checking the module path at all.
I do not understand why it was affected.
--
Best Regards
Masahiro Yamada
