[PATCH] kconfig: Proposed language extension for multiple builds
Simon Glass
sjg at chromium.org
Sat Feb 25 03:38:15 CET 2023
+Masahiro Yamada <masahiroy at kernel.org>
On Fri, 24 Feb 2023 at 19:04, Simon Glass <sjg at chromium.org> wrote:
> +lk
>
> On Sun, 19 Feb 2023 at 14:55, Simon Glass <sjg at chromium.org> wrote:
> >
> > In the case of Linux, only one build is produced so there is only a
> > single configuration. For other projects, such as U-Boot and Zephyr, the
> > same code is used to produce multiple builds, each with related (but
> > different) options enabled.
> >
> > This can be handled with the existing kconfig language, but it is quite
> > verbose, somewhat tedious and very error-prone, since there is a lot of
> > duplication. The result is hard to maintain.
> >
> > Describe an extension to the Kconfig language to support easier handling
> > of this use case.
> >
> > Signed-off-by: Simon Glass <sjg at chromium.org>
> > ---
> >
> > Documentation/kbuild/kconfig-language.rst | 134 ++++++++++++++++++++++
> > 1 file changed, 134 insertions(+)
> >
> > diff --git a/Documentation/kbuild/kconfig-language.rst
> b/Documentation/kbuild/kconfig-language.rst
> > index 858ed5d80defe..73fb016a5533f 100644
> > --- a/Documentation/kbuild/kconfig-language.rst
> > +++ b/Documentation/kbuild/kconfig-language.rst
> > @@ -228,6 +228,24 @@ applicable everywhere (see syntax).
> > enables the third modular state for all config symbols.
> > At most one symbol may have the "modules" option set.
> >
> > +- phase declaration: "defphase"
> > + This defines a new build phase. See `Build Phases`_.
> > +
> > +- default phase: "phasedefault"
> > + This indicates the default build phase. See `Build Phases`_.
> > +
> > +- add entries for phases: "addphases"
> > + This creates new phase-specific entries based on a template entry and
> adds
> > + the same attributes to it. See `Build Phases`_.
> > +
> > +- set entries for phases: "setphases"
> > + This sets the phases which need an entry. This allows creating an
> entry that
> > + only has a primary phase. See `Build Phases`_.
> > +
> > +- indicate a phase-specific attribute: "forphases"
> > + This marks an attribute as being applicable only to a particular
> phase or
> > + group of phases. See `Build Phases`_.
> > +
> > Menu dependencies
> > -----------------
> >
> > @@ -319,6 +337,119 @@ MODVERSIONS directly depends on MODULES, this
> means it's only visible if
> > MODULES is different from 'n'. The comment on the other hand is only
> > visible when MODULES is set to 'n'.
> >
> > +Build Phases
> > +------------
> > +
> > +Some projects use Kconfig to control multiple build phases, each phase
> > +resulting in a separate set of object files and executable. This is the
> > +case in U-Boot [12]_. Zephyr OS seems to be heading this way too [13]_.
> > +
> > +Generally the phases are related, so that enabling an entry in the
> primary
> > +phase also enables it by default in the others. But in some cases it may
> > +be desirable to use separate conditions for each phase.
> > +
> > +All phases have a phase name, for example `SPL`. This name is used as a
> > +prefix to each entry used in that phase, with an underscore in between.
> > +So if FOO is the primary entry, the equivalent entry for the SPL phase
> > +is SPL_FOO. The primary phase is marked with a "phasedefault" entry.
> > +
> > +Phases are declared like any other menu entry except that also have a
> > +"defphase" keyword. Phase entries are normally hidden so do not have a
> > +prompt::
> > +
> > + config PPL
> > + bool
> > + defphase "Primary Program Loader"
> > + phasedefault
> > + help
> > + This is the primary bootloader.
> > +
> > + config SPL
> > + bool
> > + defphase "Secondary Program Loader"
> > + help
> > + This is used to set up memory and load the primary bootloader.
> > +
> > +The default phase (here PPL) is assumed for all entries, in the sense
> that
> > +all entries are present in PPL by default and no prefix is needed on
> these
> > +entries. So FOO means that it applies to PPL. There must be exactly one
> > +default phase.
> > +
> > +The resulting menu entries can be used normally throughout the Kconfig.
> With
> > +this technique, the different build phases can be fully and individually
> > +controlled from Kconfig.
> > +
> > +However it is not ideal. Often the secondary phases have far fewer
> entries than
> > +the primary phase, since they offer fewer features. Even so, each FOO
> that is
> > +needed in a phase must have an SPL_FOO, etc. To avoid an explosion of
> entries,
> > +it is possible to indicate which are enabled, as a shortcut for
> creating new
> > +entries::
> > +
> > + config FOO
> > + bool "Enable foo feature"
> > + addphases SPL
> > + depends on %BAR
> > + depends on QUX
> > + forphases SPL depends on FIZZ
> > +
> > +Note that "%" expands to the phase, so this is equivalent to (ignoring
> BAR)::
> > +
> > + config FOO
> > + bool "Enable foo feature"
> > + depends on BAR
> > + depends on QUX
> > +
> > + config SPL_FOO # Phase is prepended
> > + bool "Enable foo feature (SPL)" # Suffix is added
> > + depends on SPL_BAR # "%" dependency is expanded
> > + depends on QUX
> > + depends on FIZZ # Added only for SPL
> > + depends on SPL # Added automatically
> > +
> > +Attributes declared in the primary symbol FOO (such as "depends on
> BAR") also
> > +apply to the secondary ones.
> > +
> > +An entry without any 'addphases' attribute applies to all phases.
> Individual
> > +phase entries are not available in that case. If the entry is enabled,
> then
> > +it is enabled for all phases. Only one entry appears in the resulting
> Kconfig.
> > +
> > +In the case where an entry should apply only to the primary phase (or a
> > +particular set of phases), you can uses "setphases" instead of
> "addphases"::
> > +
> > + config FOO
> > + bool "Enable foo feature"
> > + setphases PPL
> > +
> > +This means that even if the option is enabled, it will not be active
> outside
> > +the primary-phase build, here named "PPL".
> > +
> > +Internally, phases are implemented simply by creating new entries. These
> > +appear in the Kconfig as per normal. It would be possible for a Kconfig
> > +editor to show the entries just for a particular phase, leaving out the
> > +entries not applicable to that phase.
> > +
> > +When phases are used, the Kconfig tool outputs separate auto.conf files
> for
> > +each phase (e.g. auto_spl.conf), so that if SPL_FOO is enabled, then
> > +`CONFIG_FOO=y` is present in the file. This makes it easy for the build
> system
> > +to build the correct code, use IS_ENABLED(), etc.
> > +
> > +To ensure that the correct options are enabled for each build, in
> addition to
> > +the normal CONFIG_FOO option in the file, phase symbols are added too.
> For
> > +example, if FOO is enabled in the SPL phase, then auto_spl.conf
> contains::
> > +
> > + CONFIG_FOO=y
> > + CONFIG_SPL_FOO=y
> > +
> > +The phase-specific line (CONFIG_SPL_FOO) is seldom needed, but it
> allows one
> > +phase to access the symbols from another phase. For example, if the
> primary
> > +phase needs to receive boot timings from SPL, then support for boot
> timings must
> > +be added in both phases. If the timings are at a fixed address, this
> can be in a
> > +shared symbol (like CONFIG_SPL_TIMING_BASE) that both phases can access.
> > +
> > +Technical note: the grammar definition of <symbol> in this documeent
> does not
> > +include the "%" prefix at present. It can be used with any attribute.
> It cannot
> > +be used with any top-level items, like "config", "menuconfig", "if" and
> "menu".
> > +
> >
> > Kconfig syntax
> > --------------
> > @@ -744,3 +875,6 @@ https://kernelnewbies.org/KernelProjects/kconfig-sat
> > .. [9] https://www4.cs.fau.de/Publications/2011/tartler_11_eurosys.pdf
> > .. [10] https://paulgazzillo.com/papers/esecfse21.pdf
> > .. [11] https://github.com/paulgazz/kmax
> > +
> > +.. [12] https://u-boot.readthedocs.io/en/latest/develop/spl.html
> > +.. [13] https://docs.zephyrproject.org/latest/build/sysbuild/index.html
> > --
> > 2.39.2.637.g21b0678d19-goog
> >
>
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