There are three parts in the semantic analysis:
1) evaluating expressions. This is done as a simple visit
of the Expr nodes.
2) ordering clauses. This is done by constructing a graph of variables.
There is an edge from X to Y if Y depends on X, if X selects Y, or if
X appears in a conditional selection of Y; in other words, if the value
of X can affect the value of Y. Each clause has a "destination" variable
whose value can be affected by the clause, and clauses will be processed
according to a topological sorting of their destination variables.
Defaults are processed after all other clauses with the same destination.
3) deriving the value of the variables. This is done by processing
the clauses in the topological order provided by the previous step.
A "depends on" clause will force a variable to False, a "select" clause
will force a variable to True, an assignment will force a variable
to its RHS. A default will set a variable to its RHS if it has not
been set before. Because all variables have a default, after visiting
all clauses all variables will have been set.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20190123065618.3520-25-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add Python classes that represent the Kconfig abstract syntax tree.
The abstract syntax tree is stored as a list of clauses. For example:
config FOO
depends on BAR
select BAZ
is represented as three clauses:
FOO depends on BAR
FOO default n
select BAZ if FOO
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20190123065618.3520-24-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This implements a scanner and recursive descent parser for Kconfig-like
configuration files. The only "action" of the parser is for now to
detect undefined variables and process include files.
The main differences between Kconfig and this are:
* only the "bool" type is supported
* variables can only be defined once
* choices are not supported (but they could be added as syntactic
sugar for multiple Boolean values)
* menus and other graphical concepts (prompts, help text) are not
supported
* assignments ("CONFIG_FOO=y", "CONFIG_FOO=n") are parsed as part
of the Kconfig language, not as a separate file.
The idea was originally by Ákos Kovács, but I could not find his
implementation so I had to redo it.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20190123065618.3520-23-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
