| Message ID | 20210415054036.581117-1-davidgow@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] Documentation: dev-tools: Add Testing Overview | expand |
David Gow <davidgow@google.com> writes: > The kernel now has a number of testing and debugging tools, and we've > seen a bit of confusion about what the differences between them are. > > Add a basic documentation outlining the testing tools, when to use each, > and how they interact. > > This is a pretty quick overview rather than the idealised "kernel > testing guide" that'd probably be optimal, but given the number of times > questions like "When do you use KUnit and when do you use Kselftest?" > are being asked, it seemed worth at least having something. Hopefully > this can form the basis for more detailed documentation later. > > Signed-off-by: David Gow <davidgow@google.com> > Reviewed-by: Marco Elver <elver@google.com> > Reviewed-by: Daniel Latypov <dlatypov@google.com> > --- > > Thanks again. Assuming no-one has any objections, I think this is good > to go. I've applied it after fixing the conflict with docs-next. Thanks, jon
On 4/14/21 11:40 PM, David Gow wrote: > The kernel now has a number of testing and debugging tools, and we've > seen a bit of confusion about what the differences between them are. > > Add a basic documentation outlining the testing tools, when to use each, > and how they interact. > > This is a pretty quick overview rather than the idealised "kernel > testing guide" that'd probably be optimal, but given the number of times > questions like "When do you use KUnit and when do you use Kselftest?" > are being asked, it seemed worth at least having something. Hopefully > this can form the basis for more detailed documentation later. > > Signed-off-by: David Gow <davidgow@google.com> > Reviewed-by: Marco Elver <elver@google.com> > Reviewed-by: Daniel Latypov <dlatypov@google.com> > --- > > Thanks again. Assuming no-one has any objections, I think this is good > to go. > > -- David > > Changes since v2: > https://lore.kernel.org/linux-kselftest/20210414081428.337494-1-davidgow@google.com/ > - A few typo fixes (Thanks Daniel) > - Reworded description of dynamic analysis tools. > - Updated dev-tools index page to not use ':doc:' syntax, but to provide > a path instead. > - Added Marco and Daniel's Reviewed-by tags. > > Changes since v1: > https://lore.kernel.org/linux-kselftest/20210410070529.4113432-1-davidgow@google.com/ > - Note KUnit's speed and that one should provide selftests for syscalls > - Mention lockdep as a Dynamic Analysis Tool > - Refer to "Dynamic Analysis Tools" instead of "Sanitizers" > - A number of minor formatting tweaks and rewordings for clarity > > Documentation/dev-tools/index.rst | 4 + > Documentation/dev-tools/testing-overview.rst | 117 +++++++++++++++++++ > 2 files changed, 121 insertions(+) > create mode 100644 Documentation/dev-tools/testing-overview.rst > > diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst > index 1b1cf4f5c9d9..929d916ffd4c 100644 > --- a/Documentation/dev-tools/index.rst > +++ b/Documentation/dev-tools/index.rst > @@ -7,6 +7,9 @@ be used to work on the kernel. For now, the documents have been pulled > together without any significant effort to integrate them into a coherent > whole; patches welcome! > > +A brief overview of testing-specific tools can be found in > +Documentation/dev-tools/testing-overview.rst > + > .. class:: toc-title > > Table of contents > @@ -14,6 +17,7 @@ whole; patches welcome! > .. toctree:: > :maxdepth: 2 > > + testing-overview > coccinelle > sparse > kcov > diff --git a/Documentation/dev-tools/testing-overview.rst b/Documentation/dev-tools/testing-overview.rst > new file mode 100644 > index 000000000000..b5b46709969c > --- /dev/null > +++ b/Documentation/dev-tools/testing-overview.rst > @@ -0,0 +1,117 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +==================== > +Kernel Testing Guide > +==================== > + > + > +There are a number of different tools for testing the Linux kernel, so knowing > +when to use each of them can be a challenge. This document provides a rough > +overview of their differences, and how they fit together. > + > + > +Writing and Running Tests > +========================= > + > +The bulk of kernel tests are written using either the kselftest or KUnit > +frameworks. These both provide infrastructure to help make running tests and > +groups of tests easier, as well as providing helpers to aid in writing new > +tests. > + > +If you're looking to verify the behaviour of the Kernel — particularly specific > +parts of the kernel — then you'll want to use KUnit or kselftest. > + > + > +The Difference Between KUnit and kselftest > +------------------------------------------ > + > +KUnit (Documentation/dev-tools/kunit/index.rst) is an entirely in-kernel system > +for "white box" testing: because test code is part of the kernel, it can access > +internal structures and functions which aren't exposed to userspace. > + > +KUnit tests therefore are best written against small, self-contained parts > +of the kernel, which can be tested in isolation. This aligns well with the > +concept of 'unit' testing. > + > +For example, a KUnit test might test an individual kernel function (or even a > +single codepath through a function, such as an error handling case), rather > +than a feature as a whole. > + > +This also makes KUnit tests very fast to build and run, allowing them to be > +run frequently as part of the development process. > + > +There is a KUnit test style guide which may give further pointers in > +Documentation/dev-tools/kunit/style.rst > + > + > +kselftest (Documentation/dev-tools/kselftest.rst), on the other hand, is > +largely implemented in userspace, and tests are normal userspace scripts or > +programs. > + > +This makes it easier to write more complicated tests, or tests which need to > +manipulate the overall system state more (e.g., spawning processes, etc.). > +However, it's not possible to call kernel functions directly from kselftest. > +This means that only kernel functionality which is exposed to userspace somehow > +(e.g. by a syscall, device, filesystem, etc.) can be tested with kselftest. To > +work around this, some tests include a companion kernel module which exposes > +more information or functionality. If a test runs mostly or entirely within the > +kernel, however, KUnit may be the more appropriate tool. > + > +kselftest is therefore suited well to tests of whole features, as these will > +expose an interface to userspace, which can be tested, but not implementation > +details. This aligns well with 'system' or 'end-to-end' testing. > + > +For example, all new system calls should be accompanied by kselftest tests. > + > +Code Coverage Tools > +=================== > + > +The Linux Kernel supports two different code coverage measurement tools. These > +can be used to verify that a test is executing particular functions or lines > +of code. This is useful for determining how much of the kernel is being tested, > +and for finding corner-cases which are not covered by the appropriate test. > + > +:doc:`gcov` is GCC's coverage testing tool, which can be used with the kernel > +to get global or per-module coverage. Unlike KCOV, it does not record per-task > +coverage. Coverage data can be read from debugfs, and interpreted using the > +usual gcov tooling. > + > +:doc:`kcov` is a feature which can be built in to the kernel to allow > +capturing coverage on a per-task level. It's therefore useful for fuzzing and > +other situations where information about code executed during, for example, a > +single syscall is useful. > + > + > +Dynamic Analysis Tools > +====================== > + > +The kernel also supports a number of dynamic analysis tools, which attempt to > +detect classes of issues when they occur in a running kernel. These typically > +each look for a different class of bugs, such as invalid memory accesses, > +concurrency issues such as data races, or other undefined behaviour like > +integer overflows. > + > +Some of these tools are listed below: > + > +* kmemleak detects possible memory leaks. See > + Documentation/dev-tools/kmemleak.rst > +* KASAN detects invalid memory accesses such as out-of-bounds and > + use-after-free errors. See Documentation/dev-tools/kasan.rst > +* UBSAN detects behaviour that is undefined by the C standard, like integer > + overflows. See Documentation/dev-tools/ubsan.rst > +* KCSAN detects data races. See Documentation/dev-tools/kcsan.rst > +* KFENCE is a low-overhead detector of memory issues, which is much faster than > + KASAN and can be used in production. See Documentation/dev-tools/kfence.rst > +* lockdep is a locking correctness validator. See > + Documentation/locking/lockdep-design.rst > +* There are several other pieces of debug instrumentation in the kernel, many > + of which can be found in lib/Kconfig.debug > + > +These tools tend to test the kernel as a whole, and do not "pass" like > +kselftest or KUnit tests. They can be combined with KUnit or kselftest by > +running tests on a kernel with these tools enabled: you can then be sure > +that none of these errors are occurring during the test. > + > +Some of these tools integrate with KUnit or kselftest and will > +automatically fail tests if an issue is detected. > + > Thank for you writing this much needed document. Looks great. How about adding a section for Static analysis tools? A mention coccicheck scripts and mention of smatch? thanks, -- Shuah
> Thank for you writing this much needed document. Thanks, Shuah: I hope I haven't misrepresented kselftest too much. :-) > Looks great. How about adding a section for Static analysis tools? > A mention coccicheck scripts and mention of smatch? Good idea. I agree it'd be great to have such a section, though I doubt I'm the most qualified person to write it. If no one else picks it up, though, I can try to put a basic follow-up patch together when I've got some time. Cheers, -- David
diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst index 1b1cf4f5c9d9..929d916ffd4c 100644 --- a/Documentation/dev-tools/index.rst +++ b/Documentation/dev-tools/index.rst @@ -7,6 +7,9 @@ be used to work on the kernel. For now, the documents have been pulled together without any significant effort to integrate them into a coherent whole; patches welcome! +A brief overview of testing-specific tools can be found in +Documentation/dev-tools/testing-overview.rst + .. class:: toc-title Table of contents @@ -14,6 +17,7 @@ whole; patches welcome! .. toctree:: :maxdepth: 2 + testing-overview coccinelle sparse kcov diff --git a/Documentation/dev-tools/testing-overview.rst b/Documentation/dev-tools/testing-overview.rst new file mode 100644 index 000000000000..b5b46709969c --- /dev/null +++ b/Documentation/dev-tools/testing-overview.rst @@ -0,0 +1,117 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================== +Kernel Testing Guide +==================== + + +There are a number of different tools for testing the Linux kernel, so knowing +when to use each of them can be a challenge. This document provides a rough +overview of their differences, and how they fit together. + + +Writing and Running Tests +========================= + +The bulk of kernel tests are written using either the kselftest or KUnit +frameworks. These both provide infrastructure to help make running tests and +groups of tests easier, as well as providing helpers to aid in writing new +tests. + +If you're looking to verify the behaviour of the Kernel — particularly specific +parts of the kernel — then you'll want to use KUnit or kselftest. + + +The Difference Between KUnit and kselftest +------------------------------------------ + +KUnit (Documentation/dev-tools/kunit/index.rst) is an entirely in-kernel system +for "white box" testing: because test code is part of the kernel, it can access +internal structures and functions which aren't exposed to userspace. + +KUnit tests therefore are best written against small, self-contained parts +of the kernel, which can be tested in isolation. This aligns well with the +concept of 'unit' testing. + +For example, a KUnit test might test an individual kernel function (or even a +single codepath through a function, such as an error handling case), rather +than a feature as a whole. + +This also makes KUnit tests very fast to build and run, allowing them to be +run frequently as part of the development process. + +There is a KUnit test style guide which may give further pointers in +Documentation/dev-tools/kunit/style.rst + + +kselftest (Documentation/dev-tools/kselftest.rst), on the other hand, is +largely implemented in userspace, and tests are normal userspace scripts or +programs. + +This makes it easier to write more complicated tests, or tests which need to +manipulate the overall system state more (e.g., spawning processes, etc.). +However, it's not possible to call kernel functions directly from kselftest. +This means that only kernel functionality which is exposed to userspace somehow +(e.g. by a syscall, device, filesystem, etc.) can be tested with kselftest. To +work around this, some tests include a companion kernel module which exposes +more information or functionality. If a test runs mostly or entirely within the +kernel, however, KUnit may be the more appropriate tool. + +kselftest is therefore suited well to tests of whole features, as these will +expose an interface to userspace, which can be tested, but not implementation +details. This aligns well with 'system' or 'end-to-end' testing. + +For example, all new system calls should be accompanied by kselftest tests. + +Code Coverage Tools +=================== + +The Linux Kernel supports two different code coverage measurement tools. These +can be used to verify that a test is executing particular functions or lines +of code. This is useful for determining how much of the kernel is being tested, +and for finding corner-cases which are not covered by the appropriate test. + +:doc:`gcov` is GCC's coverage testing tool, which can be used with the kernel +to get global or per-module coverage. Unlike KCOV, it does not record per-task +coverage. Coverage data can be read from debugfs, and interpreted using the +usual gcov tooling. + +:doc:`kcov` is a feature which can be built in to the kernel to allow +capturing coverage on a per-task level. It's therefore useful for fuzzing and +other situations where information about code executed during, for example, a +single syscall is useful. + + +Dynamic Analysis Tools +====================== + +The kernel also supports a number of dynamic analysis tools, which attempt to +detect classes of issues when they occur in a running kernel. These typically +each look for a different class of bugs, such as invalid memory accesses, +concurrency issues such as data races, or other undefined behaviour like +integer overflows. + +Some of these tools are listed below: + +* kmemleak detects possible memory leaks. See + Documentation/dev-tools/kmemleak.rst +* KASAN detects invalid memory accesses such as out-of-bounds and + use-after-free errors. See Documentation/dev-tools/kasan.rst +* UBSAN detects behaviour that is undefined by the C standard, like integer + overflows. See Documentation/dev-tools/ubsan.rst +* KCSAN detects data races. See Documentation/dev-tools/kcsan.rst +* KFENCE is a low-overhead detector of memory issues, which is much faster than + KASAN and can be used in production. See Documentation/dev-tools/kfence.rst +* lockdep is a locking correctness validator. See + Documentation/locking/lockdep-design.rst +* There are several other pieces of debug instrumentation in the kernel, many + of which can be found in lib/Kconfig.debug + +These tools tend to test the kernel as a whole, and do not "pass" like +kselftest or KUnit tests. They can be combined with KUnit or kselftest by +running tests on a kernel with these tools enabled: you can then be sure +that none of these errors are occurring during the test. + +Some of these tools integrate with KUnit or kselftest and will +automatically fail tests if an issue is detected. +