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Masahiro Yamada b7dca6dd1e kbuild: create *.mod with full directory path and remove MODVERDIR 
While descending directories, Kbuild produces objects for modules,
but do not link final *.ko files; it is done in the modpost.

To keep track of modules, Kbuild creates a *.mod file in $(MODVERDIR)
for every module it is building. Some post-processing steps read the
necessary information from *.mod files. This avoids descending into
directories again. This mechanism was introduced in 2003 or so.

Later, commit 551559e13a ("kbuild: implement modules.order") added
modules.order. So, we can simply read it out to know all the modules
with directory paths. This is easier than parsing the first line of
*.mod files.

$(MODVERDIR) has a flat directory structure, that is, *.mod files
are named only with base names. This is based on the assumption that
the module name is unique across the tree. This assumption is really
fragile.

Stephen Rothwell reported a race condition caused by a module name
conflict:

  https://lkml.org/lkml/2019/5/13/991

In parallel building, two different threads could write to the same
$(MODVERDIR)/*.mod simultaneously.

Non-unique module names are the source of all kind of troubles, hence
commit 3a48a91901 ("kbuild: check uniqueness of module names")
introduced a new checker script.

However, it is still fragile in the build system point of view because
this race happens before scripts/modules-check.sh is invoked. If it
happens again, the modpost will emit unclear error messages.

To fix this issue completely, create *.mod with full directory path
so that two threads never attempt to write to the same file.

$(MODVERDIR) is no longer needed.

Since modules with directory paths are listed in modules.order, Kbuild
is still able to find *.mod files without additional descending.

I also killed cmd_secanalysis; scripts/mod/sumversion.c computes MD4 hash
for modules with MODULE_VERSION(). When CONFIG_DEBUG_SECTION_MISMATCH=y,
it occurs not only in the modpost stage, but also during directory
descending, where sumversion.c may parse stale *.mod files. It would emit
'No such file or directory' warning when an object consisting a module is
renamed, or when a single-obj module is turned into a multi-obj module or
vice versa.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
2019-07-18 02:19:31 +09:00
arch kbuild: add --hash-style= and --build-id unconditionally 2019-07-17 22:37:51 +09:00
block
certs
crypto
Documentation kbuild: create *.mod with full directory path and remove MODVERDIR 2019-07-18 02:19:31 +09:00
drivers scsi: remove pointless $(MODVERDIR)/$(obj)/53c700.ver 2019-07-17 22:39:27 +09:00
fs for-linus-20190715 2019-07-15 21:20:52 -07:00
include for-linus-20190715 2019-07-15 21:20:52 -07:00
init Kbuild updates for v5.3 2019-07-12 16:03:16 -07:00
ipc
kernel pci-v5.3-changes 2019-07-15 20:44:49 -07:00
lib kbuild: create *.mod with full directory path and remove MODVERDIR 2019-07-18 02:19:31 +09:00
LICENSES
mm HMM patches for 5.3 2019-07-14 19:42:11 -07:00
net pci-v5.3-changes 2019-07-15 20:44:49 -07:00
samples Kbuild updates for v5.3 2019-07-12 16:03:16 -07:00
scripts kbuild: create *.mod with full directory path and remove MODVERDIR 2019-07-18 02:19:31 +09:00
security Merge branch 'akpm' (patches from Andrew) 2019-07-12 11:40:28 -07:00
sound Driver Core and debugfs changes for 5.3-rc1 2019-07-12 12:24:03 -07:00
tools kbuild: create *.mod with full directory path and remove MODVERDIR 2019-07-18 02:19:31 +09:00
usr
virt ARM: 2019-07-12 15:35:14 -07:00
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.gitignore kbuild: create *.mod with full directory path and remove MODVERDIR 2019-07-18 02:19:31 +09:00
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Makefile kbuild: create *.mod with full directory path and remove MODVERDIR 2019-07-18 02:19:31 +09:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

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

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.