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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
..
bench treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
debug kbuild: create *.mod with full directory path and remove MODVERDIR 2019-07-18 02:19:31 +09:00
lib treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 285 2019-06-05 17:36:37 +02:00
man cpupower: correct spelling of interval 2019-06-04 09:04:08 -06:00
po cpupower: correct spelling of interval 2019-06-04 09:04:08 -06:00
utils cpupower : frequency-set -r option misses the last cpu in related cpu list 2019-06-04 09:06:50 -06:00
.gitignore tools/power/cpupower: add libcpupower.so.0.0.1 to .gitignore 2017-11-09 10:52:22 -07:00
cpupower-completion.sh cpupower : Auto-completion for cpupower tool 2018-12-05 07:52:45 -07:00
Makefile treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 167 2019-05-30 11:26:39 -07:00
README cpupower: Remove dead link to homepage, and update the targets built. 2014-05-17 00:36:36 +02:00
ToDo cpupower: Remove dead link to homepage, and update the targets built. 2014-05-17 00:36:36 +02:00

README 

The cpupower package consists of the following elements:

requirements
------------

On x86 pciutils is needed at runtime (-lpci).
For compilation pciutils-devel (pci/pci.h) and a gcc version
providing cpuid.h is needed.
For both it's not explicitly checked for (yet).


libcpupower
----------

"libcpupower" is a library which offers a unified access method for userspace
tools and programs to the cpufreq core and drivers in the Linux kernel. This
allows for code reduction in userspace tools, a clean implementation of
the interaction to the cpufreq core, and support for both the sysfs and proc
interfaces [depending on configuration, see below].


compilation and installation
----------------------------

make
su
make install

should suffice on most systems. It builds libcpupower to put in
/usr/lib; cpupower, cpufreq-bench_plot.sh to put in /usr/bin; and
cpufreq-bench to put in /usr/sbin. If you want to set up the paths
differently and/or want to configure the package to your specific
needs, you need to open "Makefile" with an editor of your choice and
edit the block marked CONFIGURATION.


THANKS
------
Many thanks to Mattia Dongili who wrote the autotoolization and
libtoolization, the manpages and the italian language file for cpupower;
to Dave Jones for his feedback and his dump_psb tool; to Bruno Ducrot for his
powernow-k8-decode and intel_gsic tools as well as the french language file;
and to various others commenting on the previous (pre-)releases of 
cpupower.


        Dominik Brodowski