dwarfinterpret/include/dwarfinterpret/DwarfInterpret.hpp

#pragma once

#include <string>
#include <memory>
#include <cstdint>

#include <dwarfpp/lib.hpp>
#include <dwarfpp/regs.hpp>
#include <dwarfpp/frame.hpp>
#include <dwarfpp/attr.hpp>
#include <dwarfpp/frame.hpp>
#include <dwarfpp/root.hpp>

#include "MemoryMap.hpp"

#define OF_WHAT_EXCEPTION(cl_name) \
    cl_name: public WhatException { \
        public:\
            cl_name(const std::string& what): WhatException(what) {} \
            cl_name() = default; \
    }

class DwarfInterpret {
    /** Singleton-ish class holding a Dwarf interpret.
     *
     * There is an instance of this class per object path from the #MemoryMap.
     * This class' interface helps making it a seamless integration, by
     * allowing to call a method for a program counter in any object path, and
     * internally passing the call to the appropriate instance.
     */

    public:  // Types, sub-classes, …
        class WhatException: public std::exception {
            /** Base exception for other exceptions, not supposed to be thrown
             * by itself */

            std::string what_str;

            public:
                /// Initialize the exception with an explanatory text chunk
                explicit WhatException(const std::string& what)
                    : what_str(what) {}

                /// Leave the explanatory text empty
                WhatException(): what_str("") {}

                /// Get the explanatory text for this exception
                const char* what() const noexcept {
                    return what_str.c_str();
                }
        };


        /** Thrown when trying to create an instance with an invalid ELF file:
         * this can mean that the file did not exist, was a special path (eg.
         * [heap]) or that it cannot be read. */
        class OF_WHAT_EXCEPTION(InvalidElf);

        /** Thrown when trying to create an instance with an ELF file that
         * contains no debug information */
        class OF_WHAT_EXCEPTION(NoDebugData);

        /** Thrown when trying to access a program counter that is not mapped
         * to an ELF file */
        class OF_WHAT_EXCEPTION(NoElfForPC);

        /** This register was needed, but is not common within DWARF
         * expressions and thus wasn't unwinded. */
        class OF_WHAT_EXCEPTION(ExoticRegister);

        /** Thrown when trying to get the value of a Dwarf register (column)
         * that is not defined or has, somehow, no value at this PC. */
        class OF_WHAT_EXCEPTION(ValuelessRegister);

        /// Thrown when accessing unimplemented parts of this library
        class OF_WHAT_EXCEPTION(NotImplemented);

        /// Thrown when somehow, getcontext (read CPU registers) fails
        class OF_WHAT_EXCEPTION(FailedGetContext);

        /// Thrown when a Dwarf element is not found for a given PC
        class OF_WHAT_EXCEPTION(NotFound);


        /// A Dwarf register
        typedef dwarf::core::FrameSection::register_def DwarfRegister;

        /// A Dwarf row of registers (for a given PC)
        typedef std::set<std::pair<int, DwarfRegister> > DwarfRow;

        /// The value type of a register's contents
        typedef uintptr_t reg_content_t;


        /** An unwind context, holding registers.
         *
         * The registers kept here should be enough for most of the unwinding
         * processes. To fully emulate libunwind, we would have to save every
         * register that is overwritten and not caller-saved.
         *
         * You'll most probably want to instanciate such a structure using
         * #DwarfInterpret::get_current_unwind_context. */
        struct UnwindContext {
            // Let's pretend this is enough
            uintptr_t rip;
            uintptr_t rsp;
            uintptr_t rbp;
        };

    public:  // methods
        DwarfInterpret(DwarfInterpret const&) = delete;
        void operator=(DwarfInterpret const&) = delete;

        /** Acquire the anonymous instance of DwarfInterpret, which works on
         * the empty memory range. Acts as a handle: passes every call to some
         * other instance */
        static DwarfInterpret& acquire();

        /** Acquire the relevant instance of #DwarfInterpret for the given
         * program counter. Instanciate it if needed. */
        static DwarfInterpret& acquire(uintptr_t pc);

        /** Get the Dwarf registers row at the given PC.
         * 
         * \throws NotFound if for some reason, the Dwarf row cannot be
         *   accessed at this PC. */
        DwarfRow dwarf_row_at(uintptr_t pc) const;

        /** Retrieves the value pointed to by the given Dwarf register
         *
         * \throws ValuelessRegister */
        reg_content_t interpret_dw_register(
                const DwarfRow& row,
                const DwarfRegister& reg,
                const UnwindContext& ctx
                ) const;

        /** Retrieves the value pointed to by the given Dwarf register
         *
         * \throws ValuelessRegister */
        reg_content_t interpret_dw_register(
                const DwarfRow& row,
                int reg_id,
                const UnwindContext& ctx
                ) const;

        /** Get the current UnwindContext (from the caller's point of view)
         *
         * **WARNING!** This context will be valid within the call frame of the
         * caller, and within descendant calls from this function, but will
         * most probably be invalid and result in weird behaviours if there is
         * only a single `return` made!
         *
         * This is supposed to work:
         * ```
         *     void foo() {
         *         UnwindContext context = get_current_unwind_context();
         *         // have fun with context
         *     }
         * ```
         *
         * While this will probably crash:
         * ```
         *     UnwindContext wrap_get_context() {
         *         return f(get_current_unwind_context());
         *     }
         *     void foo() {
         *         UnwindContext context = wrap_get_context();
         *         // have fun with context
         *     }
         * ```
         */
        static UnwindContext get_current_unwind_context();

        /// Unwinds once the given context
        UnwindContext unwind_context(const UnwindContext& ctx);

    private:
        DwarfInterpret(const MemoryMap::MapEntry& memory_object);

        DwarfRegister get_column(const DwarfRow& row, int column) const;

        const dwarf::core::FrameSection::fde_iterator fde_at(
                uintptr_t pc) const;
        const dwarf::core::FrameSection::cie_iterator cie_at(
                uintptr_t pc) const;

        /** Get the #DwarfInterpret instance responsible for the given PC, or
         * nullptr if the current instance is responsible. */
        DwarfInterpret* get_responsible_instance(uintptr_t pc) const;


    private: // members
        static MemoryMap memory_map;

        // This map maps a `memory_map` memory region index to some instance of
        // a DwarfInterpret. The special index -1 is mapped to the anonymous
        // instance.
        static std::map<int, std::unique_ptr<DwarfInterpret> > instances;

        MemoryMap::MapEntry map_entry;

        std::unique_ptr<dwarf::core::root_die> root_die;

        uintptr_t pc_offset;

        friend class std::unique_ptr<DwarfInterpret>;
};