kbuild: doc: replace arch/$(ARCH)/ with arch/$(SRCARCH)/

Precisely speaking, the arch directory is specified by $(SRCARCH),
not $(ARCH).

In old days, $(ARCH) actually matched to the arch directory because
32-bit and 64-bit were supported as separate architectures.

Most architectures (except arm/arm64) were unified like follows:

arch/i386, arch/x86_64 -> arch/x86
arch/sh, arch/sh64 -> arch/sh
arch/sparc, arch/sparc64 -> arch/sparc

To not break the user interface, commit 6752ed90da03 ("Kbuild: allow
arch/xxx to use a different source path") introduced SRCARCH to point
to the arch directory, still allowing to pass in the former ARCH=i386
or ARCH=x86_64.

Update the documents for preciseness, and add the explanation of SRCARCH.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>

docs: kbuild: fix ReST formatting

Commit cd238effefa2 ("docs: kbuild: convert docs to ReST and rename to
*.rst") missed a ReST header and a verbatim file content area.

Signed-off-by: Dov Murik <dovmurik@linux.vnet.ibm.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: doc: remove documentation about copying Module.symvers around

This is a left-over of commit 39808e451fdf ("kbuild: do not read
$(KBUILD_EXTMOD)/Module.symvers").

Kbuild no longer supports this way.

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

modpost: move the namespace field in Module.symvers last

In order to preserve backwards compatability with kmod tools, we have to
move the namespace field in Module.symvers last, as the depmod -e -E
option looks at the first three fields in Module.symvers to check symbol
versions (and it's expected they stay in the original order of crc,
symbol, module).

In addition, update an ancient comment above read_dump() in modpost that
suggested that the export type field in Module.symvers was optional. I
suspect that there were historical reasons behind that comment that are
no longer accurate. We have been unconditionally printing the export
type since 2.6.18 (commit bd5cbcedf44), which is over a decade ago now.

Fix up read_dump() to treat each field as non-optional. I suspect the
original read_dump() code treated the export field as optional in order
to support pre <= 2.6.18 Module.symvers (which did not have the export
type field). Note that although symbol namespaces are optional, the
field will not be omitted from Module.symvers if a symbol does not have
a namespace. In this case, the field will simply be empty and the next
delimiter or end of line will follow.

Cc: stable@vger.kernel.org
Fixes: cb9b55d21fe0 ("modpost: add support for symbol namespaces")
Tested-by: Matthias Maennich <maennich@google.com>
Reviewed-by: Matthias Maennich <maennich@google.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: do not read $(KBUILD_EXTMOD)/Module.symvers

Since commit 040fcc819a2e ("kbuild: improved modversioning support for
external modules"), the external module build reads Module.symvers in
the directory of the module itself, then dumps symbols back into it.
It accumulates stale symbols in the file when you build an external
module incrementally.

The idea behind it was, as the commit log explained, you can copy
Modules.symvers from one module to another when you need to pass symbol
information between two modules. However, the manual copy of the file
sounds questionable to me, and containing stale symbols is a downside.

Some time later, commit 0d96fb20b7ed ("kbuild: Add new Kbuild variable
KBUILD_EXTRA_SYMBOLS") introduced a saner approach.

So, this commit removes the former one. Going forward, the external
module build dumps symbols into Module.symvers to be carried via
KBUILD_EXTRA_SYMBOLS, but never reads it automatically.

With the -I option removed, there is no one to set the external_module
flag unless KBUILD_EXTRA_SYMBOLS is passed. Now the -i option does it
instead.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

kbuild: two minor updates for Documentation/kbuild/modules.rst

Capitalize the first word in the sentence.

Use obj-m instead of obj-y. obj-y still works, but we have no built-in
objects in external module builds. So, obj-m is better IMHO.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

kbuild: correct formatting of header in kbuild module docs

Minor formatting fixup.

Fixes: cd238effefa2 ("docs: kbuild: convert docs to ReST and rename to *.rst")
Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

modpost: add support for symbol namespaces

Add support for symbols that are exported into namespaces. For that,
extract any namespace suffix from the symbol name. In addition, emit a
warning whenever a module refers to an exported symbol without
explicitly importing the namespace that it is defined in. This patch
consistently adds the namespace suffix to symbol names exported into
Module.symvers.

Example warning emitted by modpost in case of the above violation:

WARNING: module ums-usbat uses symbol usb_stor_resume from namespace
USB_STORAGE, but does not import it.

Co-developed-by: Martijn Coenen <maco@android.com>
Signed-off-by: Martijn Coenen <maco@android.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>

docs: kbuild: convert docs to ReST and rename to *.rst

The kbuild documentation clearly shows that the documents
there are written at different times: some use markdown,
some use their own peculiar logic to split sections.

Convert everything to ReST without affecting too much
the author's style and avoiding adding uneeded markups.

The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>