fxos/include/fxos/semantics.h

//---
// fxos.semantics: Analyzed data types and locations (OS semantics)
//---

#ifndef LIBFXOS_SEMANTICS_H
#define LIBFXOS_SEMANTICS_H

#include <fxos/lang.h>
#include <fxos/domains.h>
#include <memory>
#include <variant>
#include <algorithm>

namespace FxOS {

//---
// Data type representation
//
// The abstract interpreter supports the following fixed-size data types when
// analyzing data movement and access:
//   Integers                  i8 u8 i16 u16 i32 u32        (regs, mem)
//   Bit fields over ints      T { <fields }                (regs, mem)
//   Arrays (fixed-size)       T[n]                         (mem)
//   Strings (fixed-size)      char[n]                      (mem)
//   Structures                struct { <fields> }          (mem)
//---

class DataType;

/* Base type: common information for all types (mixin) */
struct BaseType
{
	/* Type size in bytes, as would be returned by sizeof(). Must be 1, 2
	   or 4 for integral types and bit fields. Cannot be 0 because all
	   considered types are fixed-size and finite. */
	size_t size;
	/* Type alignment, can only be 1, 2 or 4 */
	size_t align;
};

/* Integer type; of byte, word or longword size. Plus signedness. This kind is
   so small that it is enumerated. */
struct IntegerType: public BaseType
{
	static DataType const *u8, *i8, *u16, *i16, *u32, *i32;

	IntegerType(size_t _size, bool _issigned) {
		size = align = _size;
		issigned = _issigned;
	}

	/* Whether the type is signed */
	bool issigned;
};

/* Bit fields over bytes, words or longwords. This should satisfy the invariant
   that the sum of the field sizes is equal to the type size. */
struct BitfieldType: public BaseType
{
	/* Fields must have positive size; the name might be empty. */
	using Field = std::pair<std::string, int>;

	std::string name;
	std::vector<Field> fields;

	/* Get field by name (throws if not found) */
	Field named_field(std::string name) const;
};

/* Homogeneous fixed-size arrays. The number of elements cannot be set to
   non-zero, and the number of elements times the size of the object type
   should equal the size of the array type. */
struct ArrayType: public BaseType
{
	struct DataType *object_type;
	int elements;
};

/* Fixed-length string. Size must be positive. */
struct StringType: public BaseType
{
	int size;
	/* Whether string stops at first NUL, or must account for all
	   characters up to the size regardless of NULs */
	bool nul_terminated;
};

/* Heterogenous structure types. */
struct StructType: public BaseType
{
	/* Fields can be of any type since all are fixed-size. */
	using Field = std::pair<std::string, DataType>;

	std::string name;
	std::vector<Field> fields;
};

/* Sum-type-style union. Basically a variant with NAMES. Thank you. */
class DataType
{
public:
	/* Variant identifier (think of it as a named sum type */
	enum DataKind { Integer=0, Bitfield=1, Array=2, String=3, Struct=4 };
	DataKind kind() const noexcept;

	/* Common properties */
	size_t size() const noexcept;
	size_t align() const noexcept;

	/* Access to type-specific data. Exactly one of these can be accessed,
	   depending on the type kind. */

	IntegerType const &integer() const;
	BitfieldType const &bitfield() const;
	ArrayType const &array() const;
	StringType const &string() const;
	StructType const &structs() const;

	/* Converting constructors from any of these types */

	DataType(IntegerType t): v(t) {}
	DataType(BitfieldType t): v(t) {}
	DataType(ArrayType t): v(t) {}
	DataType(StringType t): v(t) {}
	DataType(StructType t): v(t) {}

private:
	std::variant<IntegerType, BitfieldType, ArrayType, StringType,
	             StructType> v;
};

//---
// Data values
//
// These objects are instances of the types described by DataType. All valid
// instances are expected to be fully determined with no uninitialized memory.
//---

struct DataValue
{
	/* Each byte in the array is stored on an int16_t so that uninitialized
	   bytes can be found and diagnosed. */
	DataType const *type;
	std::vector<int16_t> mem;

	/* Create value with no memory and no tyê */
	DataValue();
	/* Create value with uninitialized memory for that data type */
	DataValue(DataType const *type);

	/* Check whether the value is fully defined and initialized */
	bool defined() {
		return std::find(mem.begin(), mem.end(), -1) == mem.end();
	}

	/* Checks that the access is correct and fits witin the value. */
	void access(size_t offset, size_t size) const;
	/* Read data from the value. Access must be 1, 2 or 4 bytes (possibly
	   unaligned) and must be in bounds. */
	uint32_t read(size_t offset, size_t size) const;
	/* Write data. Access must be 1, 2 or 4 bytes and in bounds. */
	void write(size_t offset, size_t size, uint32_t contents);

	/* Byte-based string representation */
	std::string str() const noexcept;
};

//---
// Location representation
//
// The abstract interpreter keeps track of data stored at registers, memory
// addresses and mapped modules as long as the exact location fits within the
// expressive power of a RelConst.
//---

using Location = RelConst;

} /* namespace FxOS */

#endif /* LIBFXOS_SEMANTICS_H */