Tools for working with symbolic constraints from Kbuild Makefile.
- The Kmax Tool Suite
- Quick Start
- Use Cases
- Advanced Usage
- Generating Formulas for Linux
The Kmax Tool Suite
The Kmax Tool Suite (kmaxtools) contains a set of tools for performing automated reasoning on Kconfig and Kbuild constraints. It consists of the following tools:
klocalizertakes the name of a compilation unit and automatically generates a
.configfile that, when compiled, will include the given compilation unit. It uses the logical models from
kclause"compiles" Kconfig constraints into logical formulas.
kconfig_extractoruses Linux's own Kconfig parser to perform an extraction of the syntax of configuration option names, types, dependencies, etc.
kmaxcollects configuration information from Kbuild Makefiles. It determines, for each compilation unit, a symbolic Boolean expression that represents the conditions under which the file gets compiled and linked into the final program. Its algorithm is described here and the original implementation can be found here.
- Paul Gazzillo -- creator and developer
- ThanhVu Nguyen -- developer and z3 integration into
- Jeho Oh -- developer and kclause's Kconfig logical formulas
- Julia Lawall -- ideation, evaluation
kmaxtools is currently written for python 2.
There are two ways to install kmaxtools.
The latest release can be installed via
pip install kmaxtools
pip install -U kmaxtools
Install from the source repository:
git clone https://github.com/paulgazz/kmax.git cd kmax sudo python setup.py install
Or use the
--prefixargument for different installation directory without
Please see [setup.py] for any dependencies if
setup.pyscript does not work. It may be necessary to install these manually via
pip install enum34 pip install regex pip install z3-solver pip install dd pip install networkx==2.2
The fastest way to get started is to use formulas already extracted for your version of Linux, which you can download here: https://kmaxtools.opentheblackbox.net/formulas
cd /path/to/linux/ wget https://kmaxtools.opentheblackbox.net/formulas/kmax-formulas_linux-v5.4.tar.bz2 tar -xvf kmax-formulas_linux-v5.4.tar.bz2
This contains a
.kmax directory containing the Kconfig and Kbuild
formulas for each architecture. If a version is not available
here submit an issue to request
the formulas be generated and uplodated or see below for directions on
generating these formulas.
Run klocalizer for a given compilation unit, e.g.,
This will search each architecture for constraint satisfiability,
stopping once one is found (or no architecture's constraints are
klocalizer writes this configuration to
prints the architectures, e.g.,
x86_64, to standard out.
To build the compilation unit using the generated
First set any defaults for the
make.cross ARCH=x86_64 olddefconfig
Then build the compilation unit:
make.cross ARCH=x86_64 drivers/usb/storage/alauda.o
If you cannot get a configuration or it is still not buildable, see the Troubleshooting section.
A compilation unit not built by allyesconfig
allyesconfig strives to enable all options, some have conflicting dependencies or are mutually exclusive choices. For instance,
fs/squashfs/decompressor_multi.o is not compiled when using
make allyesconfig make fs/squashfs/decompressor_multi.o
make: *** No rule to make target 'fs/squashfs/decompressor_multi.o'. Stop.
Let us take a look at the unit's Kbuild dependencies:
klocalizer --view fs/squashfs/decompressor_multi.o
The output in part is
fs/squashfs/decompressor_multi.o [And(CONFIG_SQUASHFS, CONFIG_SQUASHFS_DECOMP_MULTI)]
The unit is not included in
allyesconfig because it on both
CONFIG_SQUASHFS_DECOMP_MULTI. The latter is disabled by default, being mutually exclusive with
SQUASHFS_DECOMP_SINGLE which is selected by allyesconfig:
make allyesconfig egrep "(CONFIG_SQUASHFS|CONFIG_SQUASHFS_DECOMP_SINGLE|CONFIG_SQUASHFS_DECOMP_MULTI)( |=)" .config
grep shows us the relevant settings:
CONFIG_SQUASHFS=y CONFIG_SQUASHFS_DECOMP_SINGLE=y # CONFIG_SQUASHFS_DECOMP_MULTI is not set
klocalizer can find a configuration that includes the unit:
klocalizer fs/squashfs/decompressor_multi.o egrep "(CONFIG_SQUASHFS|CONFIG_SQUASHFS_DECOMP_SINGLE|CONFIG_SQUASHFS_DECOMP_MULTI)( |=)" .config
grep shows us what
CONFIG_SQUASHFS=y CONFIG_SQUASHFS_DECOMP_MULTI=y # CONFIG_SQUASHFS_DECOMP_SINGLE is not set
Finally, building the configuration
make olddefconfig make fs/squashfs/decompressor_multi.o
A compilation unit not built by defconfig or allnoconfig
A kernel user or developer may want a smaller kernel that includes a specific compilation unit, rather than having to build
allyesconfig. For instance,
drivers/infiniband/core/cgroup.o is not built by default:
make defconfig make drivers/infiniband/core/cgroup.o
The output contains
make: *** No rule to make target 'drivers/infiniband/core/cgroup.o'. Stop.
klocalizer can look for a configuration containing the compilation unit that closely matches a given configuration without it by successively removing conflicting constraints until the configuration is valid:
make defconfig klocalizer --approximate .config drivers/infiniband/core/cgroup.o
Now when building the configuration, the compilation unit is included:
make olddefconfig make drivers/infiniband/core/cgroup.o
The output contains:
An architecture-specific compilation unit not built by allyesconfig
Sometimes a compilation unit is only available for certain architectures. Compiling
drivers/block/ps3disk.o won't compile on an
make allyesconfig klocalizer drivers/block/ps3disk.o
Its output contains
make: *** No rule to make target 'drivers/block/ps3disk.o'. Stop.
klocalizer --view drivers/block/ps3disk.o shows us that it depends on
CONFIG_PS3_DISK. It turns out that this configuration option in turn depends on, among others options, the powerpc architecture.
klocalizer can try the constraints from each architecture:
It tells us that
powerpc is a satisfying architecture. We can use
make.cross to cross-compile for
make.cross ARCH=powerpc olddefconfig make.cross ARCH=powerpc drivers/block/ps3disk.o
Its output contains
We can combine several
klocalizer features to build an
allnoconfig kernel that adds in the
ps3disk.o compilation unit and sets all
tristate options to modules.
make.cross ARCH=powerpc allnoconfig klocalizer -a powerpc --match .config --modules --define CONFIG_MODULES drivers/block/ps3disk.o make.cross ARCH=powerpc olddefconfig make.cross ARCH=powerpc drivers/block/ps3disk.o
Its output contains
CC [M] drivers/block/ps3disk.o
An Architecture-Specific Compilation Unit
klocalizer checks each architecture's Kconfig
constraints against the Kbuild constraints for the given compilation
unit. The following are examples of how to customize this process.
Controlling the search of architectures
-ato only search a specific architecture.
klocalizer -a x86_64 drivers/usb/storage/alauda.o
-aarguments to search the given architectures in given order.
klocalizer -a x86_64 -a sparc drivers/watchdog/cpwd.o
-allto search all architectures, trying the ones given in
klocalizer -a x86_64 -a arm --all drivers/watchdog/cpwd.o
Generating an arbitrary configuration for an architecture
Pass a single architecture name without the compilation unit to generate an arbitrary configuration for that architecture. Passing multiple architectures is not supported.
klocalizer -a x86_64 drivers/watchdog/cpwd.o
Finding all architectures in which the compilation can be configured
Setting additional configuration options
--undefinearguments can be used to force configurations on or off when searching for constraints.
klocalizer --define CONFIG_USB --define CONFIG_FS --undefine CONFIG_SOUND drivers/usb/storage/alauda.o
Note that this can prevent finding a valid configuration.
klocalizer -a x86_64 --undefine CONFIG_USB drivers/usb/storage/alauda.o # no configuration possible because alauda depends on USB
Investigating unsatisfied constraints
--show-unsat-coreto see what constraints are causing the issue:
klocalizer --show-unsat-core -a x86_64 --undefine CONFIG_USB drivers/usb/storage/alauda.o # no configuration possible because alauda depends on USB
Closely match a given configuration
Klocalizer will attempt to match a given configuration, while still
maintaing the configuration options necessary to build the given
compilation unit. This works by passing it an existing configuration,
allnoconfig, with the
make allnoconfig mv .config allnoconfig klocalizer --approximate allnoconfig drivers/usb/storage/alauda.o
klocalizer with specific file
Viewing the Kbuild constraints
View the Kbuild constraints for a compilation unit and each of its subdirectories with
klocalizer --view-kbuild drivers/usb/storage/alauda.o
Building as modules instead of built-in
--modulesflag to set any tristate options to
y. Be sure to enable the
CONFIG_MODULESoption as well.
klocalizer --modules --define CONFIG_MODULES drivers/usb/storage/alauda.o make olddefconfig make drivers/block/ps3disk.o
Using new formulas
Override the default formulas with the following:
klocalizer --kmax-formula kmax --kclause-formulas kclause drivers/watchdog/cpwd.o
Generating multiple configurations
klocalizer -a x86_64 --random-seed 7849 --sample 8 --sample-prefix config
klocalizerrequires the formulas from
kclause. Download these first or generate them (see below).
CONFIG_prefix on variables when referring to them in user constraints.
.oending for compilation units (though
klocalizerwill change it automatically.)
The extracted formulas may not be exact. No resulting configuration is a sign that the formulas are overconstrained. A resulting configuration that does not include the desired compilation unit mean the formulas may be underconstrained.
Compilation unit not buildable. There are several possible reasons:
The compilation unit has already been compiled. First clean with
While most compilation units can be built individually with make, some cannot. In these cases, build the parent directory instead, e.g.,
klocalizer drivers/char/ipmi/ipmi_devintf.o # finds it buildable in x86_64 make.cross ARCH=x86_64 olddefconfig make.cross ARCH=x86_64 drivers/char/ipmi/
Composites do not correspond to source files and are not built directly via
make. Instead they are composed of other compilation units. For instance,
drivers/block/zram/zram.ois comprised of
zram_drv.o. After finding a satisfying configuration, build the parent directory to see the source files that comprise it built.
klocalizer --approximate .config drivers/block/zram/zram.o make olddefconfig make drivers/block/zram/
The configuration causes the unit to be built, but it has a compile-time error.
klocalizer drivers/block/amiflop.o # finds it buildable in make.cross ARCH=m68k olddefconfig make.cross ARCH=m68k drivers/block/amiflop.o # Makefile sees it, but causes compiler error.
Klocalizer's formulas were wrong in some cases
If the unit's configuration constraints depend on -
klocalizer, by default, which detect it and stop searching, because the compilation unit may not be (easily) compilable.
klocalizer drivers/watchdog/pnx833x_wdt.o # stops after finding a dependency on `CONFIG_BROKEN`
To get a configuration anyway, use
klocalizer --allow-config-broken drivers/watchdog/pnx833x_wdt.o # finds dependency on mips make.cross ARCH=mips olddefconfig make.cross ARCH=mips drivers/watchdog/pnx833x_wdt.o # won't be included in the build, due to CONFIG_BROKEN
Generating Formulas for Linux
This requires cloning the kmax repository, since there are helper scripts to generate the formulas for Linux. These commands and scripts are intended to be run from the root of your Linux source tree.
To get the formulas for compilation units defined in the Kbuild files, we first need a list of all the top-level source directories for each architecture. The script uses a hacky Makefile to do this. Then calls kmaxall with all of the top-level directories. This is a memory intensive operation. The next script calls kclause on each of the architectures, as named in the arch/ directory.
cd /path/to/linux mkdir -p .kmax/ /usr/bin/time bash /path/to/kmax/scripts/kmaxlinux.sh /usr/bin/time bash /path/to/kmax/scripts/kclauselinux.sh bash /path/to/kmax/scripts/packageformulaslinux.sh
This will run Kmax on the example from the paper on Kmax.
This will output the list of configuration conditions for each compilation unit file in the example Kbuild file. By default, Kmax to treat configuration options as Boolean options (as opposed to Kconfig tristate options). Pass
-T for experimental support for tristate.
unit_pc tests/kbuild/fork.o 1 unit_pc tests/kbuild/probe_32.o (CONFIG_A && CONFIG_B) unit_pc tests/kbuild/probe_64.o ((! CONFIG_A) && CONFIG_B)
unit_pc lines have the format of compilation unit name followed by the Boolean expression, in C-style syntax. The Boolean expression describes the constraints that must be satisfied for the compilation unit to be included. Use
-z to emit the z3 formulas in smtlib2 format.
Example on Linux
There is a script that will run Kmax on all Kbuild Makefiles from a project, e.g., the Linux kernel source code.
First get the Linux source and prepare its build system.
wget https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.3.11.tar.xz tar -xvf linux-5.3.11.tar.xz cd linux-5.3.11 make defconfig # any config will work here. it's just to setup the build system.
To try Kmax on a particular Kbuild Makefile, use the
This will run Kmax on a single Kbuild Makefile, and show the symbolic configurations for each compilation unit and subdirectory. Kmax can also recursively analyze Kbuild Makefiles by following subdirectories, use the
kmaxdriver.py which uses
kbuildplus.py to process each Kbuild Makefile and recursively process those in subdirectories.
-g means collect the symbolic constraints.
kmaxall -g net/
Kmax includes a Makefile hack to get all the top-level Linux directories. Combined with
kmaxall this command will collect the symbolic constraints for the whole (x86) source, saving them into
unit_pc. Be sure to change
/path/to/kmax to your kmax installation to get the Makefile shunt.
kmaxall -g $(make CC=cc ARCH=x86 -f /path/to/kmax/scripts/makefile_override alldirs) | tee kmax
Kclause extracts a logical model from Kconfig. It works in two stages:
kconfig_extractortool uses the Kconfig parser shipped with Linux to extract configuration variables dependencies to an intermediate language.
kclausetool takes this intermediate language and generates a z3 formula.
make -C kconfig_extractor
Then, from the root of a Linux source tree, run the following:
/path/to/kmax/kconfig_extractor/kconfig_extractor --extract -e ARCH=x86_64 -e SRCARCH=x86 -e KERNELVERSION=kcu -e srctree=./ -e CC=cc Kconfig > kconfig_extract kclause --remove-orphaned-nonvisible < kconfig_extract > kclause
make -C /path/to/kmax/kconfig_extractor/
Get a list of all visible configs
# all the configs that have a prompt condition grep "^prompt " kconfig.kclause | cut -f2 -d\ | sort | uniq | tee visible.txt # all the configs grep "^config " kconfig.kclause | cut -f2 -d\ | sort | uniq | tee configs.txt # the visibles should be a subset of the configs diff configs.txt visible.txt | grep ">"
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