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NAME | GENERAL APPROACH | INVOCATION | ENVIRONMENT | OPTIONS | AUTHOR | COPYRIGHT | COLOPHON |
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KMIDIFF(1) Libabigail KMIDIFF(1)
kmidiff - compare KMIs of Linux Kernel trees
kmidiff compares the binary Kernel Module Interfaces of two Linux
Kernel trees. The binary KMI is the interface that the Linux
Kernel exposes to its modules. The trees we are interested in
here are the result of the build of the Linux Kernel source tree.
And example of how to build your kernel if you want to compare it
to another one using kmidiff is:
git clone -b v4.5 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git linux/v4.5
cd linux/v4.5
make allyesconfig all
Then install the modules into a directory, for instance, the
build/modules sub-directory of the your kernel source tree:
mkdir build/modules
make modules_install INSTALL_MOD_DIR=build/modules
Then construct a list of interfaces exported by the kernel, that
you want to compare:
cat > kmi-whitelist << EOF
[kernel_4.5_kmi_whitelist]
init_task
schedule
dev_queue_xmit
__kmalloc
printk
EOF
Suppose you've done something similar for the v4.6 branch of the
Linux kernel, you now have these two directories: linux/v4.5 and
linux/v4.6. Their modules are present under the directories
linux/v4.5/build/modules and linux/v4.6/build/modules.
To Comparing their KMI kmidiff needs to know where to find the
vmlinux binaries and their associated modules. Here would be
what the command line looks like:
kmidiff \
--kmi-whitelist linux/v4.6/kmi-whitelist \
--vmlinux1 linux/v4.5/vmlinux \
--vmlinux2 linux/v4.6/vmlinux \
linux/v4.5/build/modules \
linux/v4.6/build/modules
This tool uses the libabigail library to analyze the binary as
well as its associated debug information. Here is its general
mode of operation.
When instructed to do so, a binary and its associated debug
information is read and analyzed. To that effect, libabigail
analyzes by default the descriptions of the types reachable by
the interfaces (functions and variables) that are visible outside
of their translation unit. Once that analysis is done, an
Application Binary Interface Corpus is constructed by only
considering the subset of types reachable from interfaces
associated to ELF symbols that are defined and exported by the
binary. It's that final ABI corpus which libabigail considers as
representing the ABI of the analyzed binary.
Libabigail then has capabilities to generate textual
representations of ABI Corpora, compare them, analyze their
changes and report about them.
More generally, kmidiff is invoked under the form:
kmidiff [options] <first-modules-dir> <second-modules-dir>
By default, kmidiff compares all the interfaces (exported
functions and variables) between the Kernel and its modules. In
practice, though, some users might want to compare a subset of
the those interfaces.
By default, kmidiff uses debug information in the DWARF debug
info format, if present, otherwise it compares interfaces using
CTF or BTF debug info formats, if present. Finally, if no debug
info in these formats is found, it only considers ELF symbols and
report about their addition or removal.
Users can then define a "white list" of the interfaces to
compare. Such a white list is a just a file in the "INI" format
that looks like:
[kernel_version_x86_64_whitelist]
function1_name
function2_name
global_variable1_name
....
Note that the name of the section (the name that is between the
two brackets) of that INI file just has to end with the string
"whitelist". So you can define the name you want, for instance
[kernel_46_x86_64_whitelist].
Then each line of that whitelist file is the name of an exported
function or variable. Only those interfaces along with the types
reachable from their signatures are going to be compared by
kmidiff recursively.
Note that by default kmidiff analyzes the types reachable from
the interfaces associated with ELF symbols that are defined and
exported by the Linux Kernel as being the union of the vmlinux
binary and all its compiled modules. It then compares those
interfaces (along with their types).
• --help | -h
Display a short help about the command and exit.
• --version | -v
Display the version of the program and exit.
• --verbose
Display some verbose messages while executing.
• --debug-info-dir1 | --d1 <di-path1>
For cases where the debug information for the binaries of
the first Linux kernel is split out into separate files,
tells kmidiff where to find those separate debug information
files.
Note that di-path must point to the root directory under
which the debug information is arranged in a tree-like
manner. Under Red Hat based systems, that directory is
usually <root>/usr/lib/debug.
• --debug-info-dir2 | --d2 <di-path2>
Like --debug-info-dir1, this options tells kmidiff where to
find the split debug information for the binaries of the
second Linux kernel.
• --vmlinux1 | --l1 <path-to-first-vmlinux>
Sets the path to the first vmlinux binary to consider. This
has to be the uncompressed vmlinux binary compiled with
debug info.
• --vmlinux2 | --l2 <path-to-first-vmlinux>
Sets the path to the second vmlinux binary to consider.
This has to be the uncompressed vmlinux binary compiled with
debug info.
• --kmi-whitelist | -w <path-to-interface-whitelist>
Set the path to the white list of interfaces to compare
while comparing the Kernel Module Interface of the first
kernel against the one of the second kernel.
If this option is not provided, all the exported interfaces
of the two kernels are compared. That takes a lot of times
and is not necessarily meaningful because many interface are
probably meant to see their reachable types change.
So please, make sure you always use this option unless you
really know what you are doing.
• --suppressions | --suppr <path-to-suppressions>
Use a suppression specification file located at
path-to-suppressions. Note that this option can appear
multiple times on the command line. In that case, all of
the provided suppression specification files are taken into
account.
Please note that, by default, if this option is not
provided, then the default suppression specification files
are loaded .
• --no-change-categorization | -x
This option disables the categorization of changes into
harmless and harmful changes. Note that this categorization
is a pre-requisite for the filtering of changes so this
option disables that filtering. The goal of this option is
to speed-up the execution of the program for cases where the
graph of changes is huge and where the user is just
interested in looking at, for instance, leaf node changes
without caring about their possible impact on interfaces.
• --ctf
Extract ABI information from CTF debug information, if
present, in the Kernel and Modules.
• --btf
Extract ABI information from BTF debug information, if
present, in the Kernel and Modules.
• --impacted-interfaces | -i
Tell what interfaces got impacted by each individual ABI
change.
• --full-impact | -f
Emit a change report that shows the full impact of each
change on exported interfaces. This is the default kind of
report emitted by tools like abidiff or abipkgdiff.
• --exported-interfaces-only
When using this option, this tool analyzes the descriptions
of the types reachable by the interfaces (functions and
variables) associated with ELF symbols that are defined and
exported by the Linux Kernel.
Otherwise, the tool also has the ability to analyze the
descriptions of the types reachable by the interfaces
associated with ELF symbols that are visible outside their
translation unit. This later possibility is however much
more resource intensive and results in much slower
operations.
That is why this option is enabled by default.
• --allow-non-exported-interfaces
When using this option, this tool analyzes the descriptions
of the types reachable by the interfaces (functions and
variables) that are visible outside of their translation
unit. Once that analysis is done, an ABI Corpus is
constructed by only considering the subset of types
reachable from interfaces associated to ELF symbols that are
defined and exported by the binary. It's that final ABI
corpus which is compared against another one.
The problem with that approach however is that analyzing all
the interfaces that are visible from outside their
translation unit can amount to a lot of data, leading to
very slow operations.
Note that this option is turned off by default.
• --show-bytes
Show sizes and offsets in bytes, not bits. This option is
activated by default.
• --show-bits
Show sizes and offsets in bits, not bytes. By default,
sizes and offsets are shown in bytes.
• --show-hex
Show sizes and offsets in hexadecimal base. This option is
activated by default.
• --show-dec
Show sizes and offsets in decimal base.
Dodji Seketeli
2014-2022, Red Hat, Inc.
This page is part of the libabigail (ABI Generic Analysis and
Instrumentation Library) project. Information about the project
can be found at ⟨https://sourceware.org/libabigail/⟩. If you
have a bug report for this manual page, see
⟨http://sourceware.org/bugzilla/enter_bug.cgi?product=libabigail⟩.
This page was obtained from the project's upstream Git repository
⟨git://sourceware.org/git/libabigail.git⟩ on 2024-06-14. (At
that time, the date of the most recent commit that was found in
the repository was 2024-05-31.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Jun 14, 2024 KMIDIFF(1)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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