[PATCH] kconfig: Proposed language extension for multiple builds
Masahiro Yamada
masahiroy at kernel.org
Sun Feb 26 04:31:00 CET 2023
On Sat, Feb 25, 2023 at 11:38 AM Simon Glass <sjg at chromium.org> wrote:
>
> +Masahiro Yamada
I do not know.
This seems a shorthand in Kconfig level.
masahiro at zoe:~/ref/u-boot(master)$ rgrep '^config SPL_' | wc
540 1080 24872
masahiro at zoe:~/ref/u-boot(master)$ rgrep '^config TPL_' | wc
163 326 7462
If hundreds of duplications are not manageable,
go for it, but kconfig will be out-of-sync from the
upstream Kconfig.
Masahiro
> 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
>> >
--
Best Regards
Masahiro Yamada
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