commit 23a0cb8e3225122496bfa79172005c587c2d64bf upstream.

When building an external module, if users don't need to separate the
compilation output and source code, they run the following command:
"make -C $(LINUX_SRC_DIR) M=$(PWD)". At this point, "$(KBUILD_EXTMOD)"
and "$(src)" are the same.

If they need to separate them, they run "make -C $(KERNEL_SRC_DIR)
O=$(KERNEL_OUT_DIR) M=$(OUT_DIR) src=$(PWD)". Before running the
command, they need to copy "Kbuild" or "Makefile" to "$(OUT_DIR)" to
prevent compilation failure.

So the kernel should change the included path to avoid the copy operation.

Signed-off-by: Jing Leng <jleng@ambarella.com>
[masahiro: I do not think "M=$(OUT_DIR) src=$(PWD)" is the official way,
but this patch is a nice clean up anyway.]
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nicolas Schier <n.schier@avm.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

[ Upstream commit 69bc8d386aebbd91a6bb44b6d33f77c8dfa9ed8c ]

The external module build shows the following warning if Module.symvers
is missing in the kernel tree.

  WARNING: Symbol version dump "Module.symvers" is missing.
           Modules may not have dependencies or modversions.

I think this is an important heads-up because the resulting modules may
not work as expected. This happens when you did not build the entire
kernel tree, for example, you might have prepared the minimal setups
for external modules by 'make defconfig && make modules_preapre'.

A problem is that 'make modules' creates Module.symvers even without
vmlinux. In this case, that warning is suppressed since Module.symvers
already exists in spite of its incomplete content.

The incomplete (i.e. invalid) Module.symvers should not be created.

This commit changes the second pass of modpost to dump symbols into
modules-only.symvers. The final Module.symvers is created by
concatenating vmlinux.symvers and modules-only.symvers if both exist.

Module.symvers is supposed to collect symbols from both vmlinux and
modules. It might be a bit confusing, and I am not quite sure if it
is an official interface, but presumably it is difficult to rename it
because some tools (e.g. kmod) parse it.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

The same code exists a few lines above.

Fixes: 436b2ac603d5 ("modpost: invoke modpost only when input files are updated")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Collect options for modules into a single place.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

The -s option was added by commit 8d8d8289df65 ("kbuild: do not do
section mismatch checks on vmlinux in 2nd pass").

Now that the second pass does not parse vmlinux, this option is
unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

If modpost fails to load a symbol dump file, it cannot check unresolved
symbols, hence module dependency will not be added. Nor CRCs can be added.

Currently, external module builds check only $(objtree)/Module.symvers,
but it should check files specified by KBUILD_EXTRA_SYMBOLS as well.

Move the warning message from the top Makefile to scripts/Makefile.modpost
and print the warning if any dump file is missing.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Currently, the second pass of modpost is always invoked when you run
'make' or 'make modules' even if none of modules is changed.

Use if_changed to invoke it only when it is necessary.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

The full build runs modpost twice, first for vmlinux.o and second for
modules.

The first pass dumps all the vmlinux symbols into Module.symvers, but
the second pass parses vmlinux again instead of reusing the dump file,
presumably because it needs to avoid accumulating stale symbols.

Loading symbol info from a dump file is faster than parsing an ELF object.
Besides, modpost deals with various issues to parse vmlinux in the second
pass.

A solution is to make the first pass dumps symbols into a separate file,
vmlinux.symvers. The second pass reads it, and parses module .o files.
The merged symbol information is dumped into Module.symvers in the same
way as before.

This makes further modpost cleanups possible.

Also, it fixes the problem of 'make vmlinux', which previously overwrote
Module.symvers, throwing away module symbols.

I slightly touched scripts/link-vmlinux.sh so that vmlinux is re-linked
when you cross this commit. Otherwise, vmlinux.symvers would not be
generated.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Prepare to use -i for in-tree modpost as well.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

The symbol dump *.symvers is the output of modpost. Print it in
the short log.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>