From 1c199f2878f6c1b8c52125ad9805e94fe2dde472 Mon Sep 17 00:00:00 2001 From: "Luis R. Rodriguez" Date: Wed, 7 Oct 2015 16:16:33 -0700 Subject: kbuild: document recursive dependency limitation / resolution Recursive dependency issues with kconfig are unavoidable due to some limitations with kconfig, since these issues are recurring provide a hint to the user how they can resolve these dependency issues and also document why such limitation exists. While at it also document a bit of future prospects of ways to enhance Kconfig, including providing formal semantics and evaluation of use of a SAT solver. If you're interested in this work or prospects of it check out the kconfig-sat project wiki [0] and mailing list [1]. [0] http://kernelnewbies.org/KernelProjects/kconfig-sat [1] https://groups.google.com/d/forum/kconfig-sat Cc: Geert Uytterhoeven Cc: James Bottomley Cc: Josh Triplett Cc: Paul Bolle Cc: Herbert Xu Cc: Takashi Iwai Cc: "Yann E. MORIN" Cc: Jonathan Corbet Cc: Mate Soos Signed-off-by: Luis R. Rodriguez Signed-off-by: Michal Marek --- Documentation/kbuild/Kconfig.select-break | 33 +++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) create mode 100644 Documentation/kbuild/Kconfig.select-break (limited to 'Documentation/kbuild/Kconfig.select-break') diff --git a/Documentation/kbuild/Kconfig.select-break b/Documentation/kbuild/Kconfig.select-break new file mode 100644 index 000000000000..365ceb3424b1 --- /dev/null +++ b/Documentation/kbuild/Kconfig.select-break @@ -0,0 +1,33 @@ +# Select broken dependency issue +# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +# +# Test with: +# +# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.select-break menuconfig +# +# kconfig will not complain and enable this layout for configuration. This is +# currently a feature of kconfig, given select was designed to be heavy handed. +# Kconfig currently does not check the list of symbols listed on a symbol's +# "select" list, this is done on purpose to help load a set of known required +# symbols. Because of this use of select should be used with caution. An +# example of this issue is below. +# +# The option B and C are clearly contradicting with respect to A. +# However, when A is set, C can be set as well because Kconfig does not +# visit the dependencies of the select target (in this case B). And since +# Kconfig does not visit the dependencies, it breaks the dependencies of B +# (!A). + +mainmenu "Simple example to demo kconfig select broken dependency issue" + +config A + bool "CONFIG A" + +config B + bool "CONFIG B" + depends on !A + +config C + bool "CONFIG C" + depends on A + select B -- cgit v1.2.3