path: root/Documentation/kbuild/
diff options
authorLuis R. Rodriguez <>2015-10-07 16:16:33 -0700
committerMichal Marek <>2015-10-08 15:36:16 +0200
commit1c199f2878f6c1b8c52125ad9805e94fe2dde472 (patch)
tree8f2ecef49d9db9fd3aceeee186cff1959ebb2502 /Documentation/kbuild/
parent6ff33f3902c3b1c5d0db6b1e2c70b6d76fba357f (diff)
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] [1] 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 <>
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+# Select broken dependency issue
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+# Test with:
+# make KBUILD_KCONFIG=Documentation/kbuild/ 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