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authorLinus Torvalds <torvalds@linux-foundation.org>2018-06-06 11:31:45 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-06-06 11:31:45 -0700
commit0ad39cb3d70fb4324d127aeceee7f63e3f71605c (patch)
tree627d885a698b485d13be0140fe7e6881486fbd11 /Documentation
parent8715ee75fe6fa3aed367f28aa7a3655e6a8e4688 (diff)
parent2ae89c7a82ea9d81a19b4fc2df23bef4b112f24e (diff)
Merge tag 'kconfig-v4.18' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kconfig updates from Masahiro Yamada: "Kconfig now supports new functionality to perform textual substitution. It has been a while since Linus suggested to move compiler option tests from makefiles to Kconfig. Finally, here it is. The implementation has been generalized into a Make-like macro language. Some built-in functions such as 'shell' are provided. Variables and user-defined functions are also supported so that 'cc-option', 'ld-option', etc. are implemented as macros. Summary: - refactor package checks for building {m,n,q,g}conf - remove unused/unmaintained localization support - remove Kbuild cache - drop CONFIG_CROSS_COMPILE support - replace 'option env=' with direct variable expansion - add built-in functions such as 'shell' - support variables and user-defined functions - add helper macros as as 'cc-option' - add unit tests and a document of the new macro language - add 'testconfig' to help - fix warnings from GCC 8.1" * tag 'kconfig-v4.18' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (30 commits) kconfig: Avoid format overflow warning from GCC 8.1 kbuild: Move last word of nconfig help to the previous line kconfig: Add testconfig into make help output kconfig: add basic helper macros to scripts/Kconfig.include kconfig: show compiler version text in the top comment kconfig: test: add Kconfig macro language tests Documentation: kconfig: document a new Kconfig macro language kconfig: error out if a recursive variable references itself kconfig: add 'filename' and 'lineno' built-in variables kconfig: add 'info', 'warning-if', and 'error-if' built-in functions kconfig: expand lefthand side of assignment statement kconfig: support append assignment operator kconfig: support simply expanded variable kconfig: support user-defined function and recursively expanded variable kconfig: begin PARAM state only when seeing a command keyword kconfig: replace $(UNAME_RELEASE) with function call kconfig: add 'shell' built-in function kconfig: add built-in function support kconfig: make default prompt of mainmenu less specific kconfig: remove sym_expand_string_value() ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/kbuild/kconfig-language.txt8
-rw-r--r--Documentation/kbuild/kconfig-macro-language.txt242
2 files changed, 242 insertions, 8 deletions
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
index f5b9493f04ad..0e966e8f9ec7 100644
--- a/Documentation/kbuild/kconfig-language.txt
+++ b/Documentation/kbuild/kconfig-language.txt
@@ -198,14 +198,6 @@ applicable everywhere (see syntax).
enables the third modular state for all config symbols.
At most one symbol may have the "modules" option set.
- - "env"=<value>
- This imports the environment variable into Kconfig. It behaves like
- a default, except that the value comes from the environment, this
- also means that the behaviour when mixing it with normal defaults is
- undefined at this point. The symbol is currently not exported back
- to the build environment (if this is desired, it can be done via
- another symbol).
-
- "allnoconfig_y"
This declares the symbol as one that should have the value y when
using "allnoconfig". Used for symbols that hide other symbols.
diff --git a/Documentation/kbuild/kconfig-macro-language.txt b/Documentation/kbuild/kconfig-macro-language.txt
new file mode 100644
index 000000000000..07da2ea68dce
--- /dev/null
+++ b/Documentation/kbuild/kconfig-macro-language.txt
@@ -0,0 +1,242 @@
+Concept
+-------
+
+The basic idea was inspired by Make. When we look at Make, we notice sort of
+two languages in one. One language describes dependency graphs consisting of
+targets and prerequisites. The other is a macro language for performing textual
+substitution.
+
+There is clear distinction between the two language stages. For example, you
+can write a makefile like follows:
+
+ APP := foo
+ SRC := foo.c
+ CC := gcc
+
+ $(APP): $(SRC)
+ $(CC) -o $(APP) $(SRC)
+
+The macro language replaces the variable references with their expanded form,
+and handles as if the source file were input like follows:
+
+ foo: foo.c
+ gcc -o foo foo.c
+
+Then, Make analyzes the dependency graph and determines the targets to be
+updated.
+
+The idea is quite similar in Kconfig - it is possible to describe a Kconfig
+file like this:
+
+ CC := gcc
+
+ config CC_HAS_FOO
+ def_bool $(shell, $(srctree)/scripts/gcc-check-foo.sh $(CC))
+
+The macro language in Kconfig processes the source file into the following
+intermediate:
+
+ config CC_HAS_FOO
+ def_bool y
+
+Then, Kconfig moves onto the evaluation stage to resolve inter-symbol
+dependency as explained in kconfig-language.txt.
+
+
+Variables
+---------
+
+Like in Make, a variable in Kconfig works as a macro variable. A macro
+variable is expanded "in place" to yield a text string that may then be
+expanded further. To get the value of a variable, enclose the variable name in
+$( ). The parentheses are required even for single-letter variable names; $X is
+a syntax error. The curly brace form as in ${CC} is not supported either.
+
+There are two types of variables: simply expanded variables and recursively
+expanded variables.
+
+A simply expanded variable is defined using the := assignment operator. Its
+righthand side is expanded immediately upon reading the line from the Kconfig
+file.
+
+A recursively expanded variable is defined using the = assignment operator.
+Its righthand side is simply stored as the value of the variable without
+expanding it in any way. Instead, the expansion is performed when the variable
+is used.
+
+There is another type of assignment operator; += is used to append text to a
+variable. The righthand side of += is expanded immediately if the lefthand
+side was originally defined as a simple variable. Otherwise, its evaluation is
+deferred.
+
+The variable reference can take parameters, in the following form:
+
+ $(name,arg1,arg2,arg3)
+
+You can consider the parameterized reference as a function. (more precisely,
+"user-defined function" in contrast to "built-in function" listed below).
+
+Useful functions must be expanded when they are used since the same function is
+expanded differently if different parameters are passed. Hence, a user-defined
+function is defined using the = assignment operator. The parameters are
+referenced within the body definition with $(1), $(2), etc.
+
+In fact, recursively expanded variables and user-defined functions are the same
+internally. (In other words, "variable" is "function with zero argument".)
+When we say "variable" in a broad sense, it includes "user-defined function".
+
+
+Built-in functions
+------------------
+
+Like Make, Kconfig provides several built-in functions. Every function takes a
+particular number of arguments.
+
+In Make, every built-in function takes at least one argument. Kconfig allows
+zero argument for built-in functions, such as $(fileno), $(lineno). You could
+consider those as "built-in variable", but it is just a matter of how we call
+it after all. Let's say "built-in function" here to refer to natively supported
+functionality.
+
+Kconfig currently supports the following built-in functions.
+
+ - $(shell,command)
+
+ The "shell" function accepts a single argument that is expanded and passed
+ to a subshell for execution. The standard output of the command is then read
+ and returned as the value of the function. Every newline in the output is
+ replaced with a space. Any trailing newlines are deleted. The standard error
+ is not returned, nor is any program exit status.
+
+ - $(info,text)
+
+ The "info" function takes a single argument and prints it to stdout.
+ It evaluates to an empty string.
+
+ - $(warning-if,condition,text)
+
+ The "warning-if" function takes two arguments. If the condition part is "y",
+ the text part is sent to stderr. The text is prefixed with the name of the
+ current Kconfig file and the current line number.
+
+ - $(error-if,condition,text)
+
+ The "error-if" function is similar to "warning-if", but it terminates the
+ parsing immediately if the condition part is "y".
+
+ - $(filename)
+
+ The 'filename' takes no argument, and $(filename) is expanded to the file
+ name being parsed.
+
+ - $(lineno)
+
+ The 'lineno' takes no argument, and $(lineno) is expanded to the line number
+ being parsed.
+
+
+Make vs Kconfig
+---------------
+
+Kconfig adopts Make-like macro language, but the function call syntax is
+slightly different.
+
+A function call in Make looks like this:
+
+ $(func-name arg1,arg2,arg3)
+
+The function name and the first argument are separated by at least one
+whitespace. Then, leading whitespaces are trimmed from the first argument,
+while whitespaces in the other arguments are kept. You need to use a kind of
+trick to start the first parameter with spaces. For example, if you want
+to make "info" function print " hello", you can write like follows:
+
+ empty :=
+ space := $(empty) $(empty)
+ $(info $(space)$(space)hello)
+
+Kconfig uses only commas for delimiters, and keeps all whitespaces in the
+function call. Some people prefer putting a space after each comma delimiter:
+
+ $(func-name, arg1, arg2, arg3)
+
+In this case, "func-name" will receive " arg1", " arg2", " arg3". The presence
+of leading spaces may matter depending on the function. The same applies to
+Make - for example, $(subst .c, .o, $(sources)) is a typical mistake; it
+replaces ".c" with " .o".
+
+In Make, a user-defined function is referenced by using a built-in function,
+'call', like this:
+
+ $(call my-func,arg1,arg2,arg3)
+
+Kconfig invokes user-defined functions and built-in functions in the same way.
+The omission of 'call' makes the syntax shorter.
+
+In Make, some functions treat commas verbatim instead of argument separators.
+For example, $(shell echo hello, world) runs the command "echo hello, world".
+Likewise, $(info hello, world) prints "hello, world" to stdout. You could say
+this is _useful_ inconsistency.
+
+In Kconfig, for simpler implementation and grammatical consistency, commas that
+appear in the $( ) context are always delimiters. It means
+
+ $(shell, echo hello, world)
+
+is an error because it is passing two parameters where the 'shell' function
+accepts only one. To pass commas in arguments, you can use the following trick:
+
+ comma := ,
+ $(shell, echo hello$(comma) world)
+
+
+Caveats
+-------
+
+A variable (or function) cannot be expanded across tokens. So, you cannot use
+a variable as a shorthand for an expression that consists of multiple tokens.
+The following works:
+
+ RANGE_MIN := 1
+ RANGE_MAX := 3
+
+ config FOO
+ int "foo"
+ range $(RANGE_MIN) $(RANGE_MAX)
+
+But, the following does not work:
+
+ RANGES := 1 3
+
+ config FOO
+ int "foo"
+ range $(RANGES)
+
+A variable cannot be expanded to any keyword in Kconfig. The following does
+not work:
+
+ MY_TYPE := tristate
+
+ config FOO
+ $(MY_TYPE) "foo"
+ default y
+
+Obviously from the design, $(shell command) is expanded in the textual
+substitution phase. You cannot pass symbols to the 'shell' function.
+The following does not work as expected.
+
+ config ENDIAN_FLAG
+ string
+ default "-mbig-endian" if CPU_BIG_ENDIAN
+ default "-mlittle-endian" if CPU_LITTLE_ENDIAN
+
+ config CC_HAS_ENDIAN_FLAG
+ def_bool $(shell $(srctree)/scripts/gcc-check-flag ENDIAN_FLAG)
+
+Instead, you can do like follows so that any function call is statically
+expanded.
+
+ config CC_HAS_ENDIAN_FLAG
+ bool
+ default $(shell $(srctree)/scripts/gcc-check-flag -mbig-endian) if CPU_BIG_ENDIAN
+ default $(shell $(srctree)/scripts/gcc-check-flag -mlittle-endian) if CPU_LITTLE_ENDIAN