Describes most data srtructures used in sparse. --- Documentation/data-structures.txt | 54 +++++++++++++++++++++++++++++++++++++ 1 files changed, 54 insertions(+), 0 deletions(-) create mode 100644 Documentation/data-structures.txt diff --git a/Documentation/data-structures.txt b/Documentation/data-structures.txt new file mode 100644 index 0000000..3745b54 --- /dev/null +++ b/Documentation/data-structures.txt @@ -0,0 +1,54 @@ + +<JoshTriplett> As far as the parsing structures go... +<JoshTriplett> The C parser exists in two main files: parse.c, which parses statements, and expression.c, which parses expressions. +<JoshTriplett> parse.h contains the definition of struct statement, which represents a C statement. +<JoshTriplett> That includes only those things which can't appear as an expression, which primarily includes control flow statements such as if, loops, switch/case, and goto. +<JoshTriplett> expression.h contains the definition of struct expression, which represents a C expression. That has a lot more content, since most C constructs can appear in expressions. +<JoshTriplett> A series of statements forms a compound statement (STMT_COMPOUND). +<JoshTriplett> That appears as another struct statement which has a statement_list member. +<JoshTriplett> A function body consists of a compound statement. +<JoshTriplett> When you look at a loop body, if or else body, or case body, you'll notice that they just have a struct statement, not a statement_list; they can have multiple statements by using a compound statement. +<JoshTriplett> Also note that all loops get turned into a single "iterator" statement. +<JoshTriplett> for, while, and do-while. +<JoshTriplett> A symbol, then, represents a name in a C file. A symbol might represent a variable, a function, a label, or various other things. +<JoshTriplett> See symbol.h. +<JoshTriplett> "struct symbol" represents one symbol. +<JoshTriplett> As with the various other structures, it has some common data and a union of sub-structures for the parts that differ between different types. +<JoshTriplett> Most of the interesting bits come in the NS_SYMBOL case. +<JoshTriplett> Among other things, it has a struct statement for the body of a function (if any), a list of symbols for the arguments, an expression for a variable initializer, and so on. +<JoshTriplett> Together, struct symbol, struct statement, and struct expression represent most of the abstract syntax tree for C. +<JoshTriplett> So, that represents most of the "front-end" of Sparse: parsing C and generating that abstract syntax tree. +<JoshTriplett> That much occurs in pretty much any program using the Sparse frontend. +<JoshTriplett> The backend varies among programs. +<JoshTriplett> For instance, the c2xml backend goes that far, then outputs XML. +<JoshTriplett> The sparse static analysis backend has a few steps: it generates linearized bytecode, does some evaluation on that, and outputs some warnings. +<JoshTriplett> Several other backends run that linearized bytecode stage. +<JoshTriplett> The linearized bytecode itself has a set of nested structures. +<JoshTriplett> linearize.h defines all of them. +<JoshTriplett> At the top level, it has struct entrypoint. +<JoshTriplett> That represents an entrypoint to the code, which would normally mean a function. +<JoshTriplett> An entrypoint has a list of basic blocks. +<JoshTriplett> struct basic_block. +<JoshTriplett> A basic block represents a series of instructions with no branches. +<JoshTriplett> Straight-line code. +<JoshTriplett> A branch only occurs at the end of a basic block, and branches can only target the beginning of a basic block. +<JoshTriplett> Typically, a conditional will consist of a basic block leading up to the branch, a basic block for the true case, a basic block for the false case, and a basic block where the two paths merge back together. +<JoshTriplett> Either the true or the false case may not exist. +<JoshTriplett> A loop will normally have a basic block for the loop body, which can branch to the top at the end or continue to the next basic block. +<JoshTriplett> So basic blocks represent a node in the control flow graph. +<JoshTriplett> The edges in that graph lead from one basic block to a basic block which can follow it in the execution of the program. +<JoshTriplett> Each basic block has a series of instructions, "struct instruction". +<JoshTriplett> "enum opcode" lists all the instructions. +<JoshTriplett> Fairly high-level instruction set, corresponding directly to bits of C. +<JoshTriplett> So you have an entrypoint, which has a graph of basic blocks, each of which has a list of instructions. +<JoshTriplett> An entrypoint also has a pointer to the first instruction. +<JoshTriplett> One last bit of trickiness: struct pseudo. +<JoshTriplett> Have you ever heard of "static single assignment" or SSA form? +<JoshTriplett> struct pseudo represents one of those single-assignment variables. +<JoshTriplett> Each one has a pointer to the symbol it represents (which may have many pseudos referencing it). +<JoshTriplett> Each one also has a pointer to the instruction that defines it. +<JoshTriplett> That covers most of the major data structures in Sparse. +<JoshTriplett> Now, given all that, some of the top-level stuff in sparse.c may make more sense. +<JoshTriplett> For instance, the context checking works in terms of basic blocks. +<JoshTriplett> Hopefully some of that helped you understand Sparse better. + -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
