src/arch/arm/semihosting.hh - public/gem5 - Git at Google

 /*
  * Copyright (c) 2018, 2019 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
  * not be construed as granting a license to any other intellectual
  * property including but not limited to intellectual property relating
  * to a hardware implementation of the functionality of the software
  * licensed hereunder.  You may use the software subject to the license
  * terms below provided that you ensure that this notice is replicated
  * unmodified and in its entirety in all distributions of the software,
  * modified or unmodified, in source code or in binary form.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met: redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer;
  * redistributions in binary form must reproduce the above copyright
  * notice, this list of conditions and the following disclaimer in the
  * documentation and/or other materials provided with the distribution;
  * neither the name of the copyright holders nor the names of its
  * contributors may be used to endorse or promote products derived from
  * this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #ifndef __ARCH_ARM_SEMIHOSTING_HH__
 #define __ARCH_ARM_SEMIHOSTING_HH__

 #include <cstdio>
 #include <functional>
 #include <map>
 #include <memory>
 #include <utility>
 #include <vector>

 #include "arch/arm/intregs.hh"
 #include "arch/arm/utility.hh"
 #include "cpu/thread_context.hh"
 #include "mem/port_proxy.hh"
 #include "sim/guest_abi.hh"
 #include "sim/sim_object.hh"

 struct ArmSemihostingParams;
 class SerialDevice;

 /**
  * Semihosting for AArch32 and AArch64
  *
  * This class implements the Arm semihosting interface. This interface
  * allows baremetal code access service, such as IO, from the
  * simulator. It is conceptually a simplified version of gem5's more
  * general syscall emulation mode.
  *
  * Exits calls (SYS_EXIT, SYS_EXIT_EXTENDED) from the guest get
  * translated into simualtion exits. Well-known exit codes are
  * translated to messages on the form 'semi:ADP_.*' while unknown
  * codes are returned in hex ('semi:0x..'). The subcode is reported in
  * the gem5 exit event.
  */
 class ArmSemihosting : public SimObject
 {
   public:

     enum {
         // Standard ARM immediate values which trigger semihosting.
         T32Imm = 0xAB,
         A32Imm = 0x123456,
         A64Imm = 0xF000,

         // The immediate value which enables gem5 semihosting calls. Use the
         // standard value for thumb.
         Gem5Imm = 0x5D57
     };

     static PortProxy &portProxy(ThreadContext *tc);

     struct AbiBase
     {
         template <typename Arg>
         class StateBase
         {
           private:
             Addr argPointer;
             ByteOrder endian;

           public:
             StateBase(const ThreadContext *tc, Addr arg_pointer) :
                 argPointer(arg_pointer), endian(ArmISA::byteOrder(tc))
             {}

             /*
              * These two methods are used to both read an argument or its
              * address, and to move position on to the next location. Normally
              * State would be more passive, but since it behaves almost the
              * same no matter what the argument type is we can simplify and
              * consolidate a little bit by centralizing these methods.
              */

             // Return the address of an argument slot and move past it.
             Addr
             getAddr()
             {
                 Addr addr = argPointer;
                 argPointer += sizeof(Arg);
                 return addr;
             }

             // Read the value in an argument slot and move past it.
             Arg
             get(ThreadContext *tc)
             {
                 Arg arg = ArmSemihosting::portProxy(tc).read<Arg>(
                         argPointer, endian);
                 argPointer += sizeof(Arg);
                 return arg;
             }

             using ArgType = Arg;
         };
     };

     struct Abi64 : public AbiBase
     {
         class State : public StateBase<uint64_t>
         {
           public:
             // For 64 bit semihosting, the params are pointer to by X1.
             explicit State(const ThreadContext *tc) :
                 StateBase<uint64_t>(tc, tc->readIntReg(ArmISA::INTREG_X1))
             {}
         };
     };

     struct Abi32 : public AbiBase
     {
         class State : public StateBase<uint64_t>
         {
           public:
             // For 32 bit semihosting, the params are pointer to by R1.
             explicit State(const ThreadContext *tc) :
                 StateBase<uint64_t>(tc, tc->readIntReg(ArmISA::INTREG_R1))
             {}
         };
     };

     // Use this argument type when you need to modify an argument in place.
     // This will give you the address of the argument itself and the size of
     // each argument slot, rather than the actual value of the argument.
     struct InPlaceArg
     {
         Addr addr;
         size_t size;

         InPlaceArg(Addr _addr, size_t _size) : addr(_addr), size(_size) {}

         // A helper function to read the argument since the guest ABI mechanism
         // didn't do that for us.
         uint64_t
         read(ThreadContext *tc, ByteOrder endian)
         {
             auto &proxy = ArmSemihosting::portProxy(tc);
             if (size == 8)
                 return proxy.read<uint64_t>(addr, endian);
             else if (size == 4)
                 return proxy.read<uint32_t>(addr, endian);
             else
                 panic("Unexpected semihosting argument size %d.", size);
         }

         // A helper function to write to the argument's slot in the params.
         void
         write(ThreadContext *tc, uint64_t val, ByteOrder endian)
         {
             auto &proxy = ArmSemihosting::portProxy(tc);
             if (size == 8)
                 proxy.write<uint64_t>(addr, val, endian);
             else if (size == 4)
                 proxy.write<uint32_t>(addr, val, endian);
             else
                 panic("Unexpected semihosting argument size %d.", size);
         }
     };

     enum Operation {
         SYS_OPEN = 0x01,
         SYS_CLOSE = 0x02,
         SYS_WRITEC = 0x03,
         SYS_WRITE0 = 0x04,
         SYS_WRITE = 0x05,
         SYS_READ = 0x06,
         SYS_READC = 0x07,
         SYS_ISERROR = 0x08,
         SYS_ISTTY = 0x09,
         SYS_SEEK = 0x0A,
         SYS_FLEN = 0x0C,
         SYS_TMPNAM = 0x0D,
         SYS_REMOVE = 0x0E,
         SYS_RENAME = 0x0F,
         SYS_CLOCK = 0x10,
         SYS_TIME = 0x11,
         SYS_SYSTEM = 0x12,
         SYS_ERRNO = 0x13,
         SYS_GET_CMDLINE = 0x15,
         SYS_HEAPINFO = 0x16,
         SYS_EXIT = 0x18,
         SYS_EXIT_EXTENDED = 0x20,
         SYS_ELAPSED = 0x30,
         SYS_TICKFREQ = 0x31,

         MaxStandardOp = 0xFF,

         SYS_GEM5_PSEUDO_OP = 0x100
     };

     ArmSemihosting(const ArmSemihostingParams *p);

     /** Perform an Arm Semihosting call from aarch64 code. */
     bool call64(ThreadContext *tc, bool gem5_ops);
     /** Perform an Arm Semihosting call from aarch32 code. */
     bool call32(ThreadContext *tc, bool gem5_ops);

   public: // SimObject and related interfaces
     void serialize(CheckpointOut &cp) const override;
     void unserialize(CheckpointIn &cp) override;

   protected: // Configuration
     const std::string cmdLine;
     const Addr memReserve;
     const Addr stackSize;

     /**
      * Base time when the simulation started. This is used to
      * calculate the time of date when the guest call SYS_TIME.
      */
     const time_t timeBase;

     /** Number of bits to right shift gem5 ticks to fit in a uint32_t */
     const unsigned tickShift;

   protected: // Internal state
     typedef uint64_t SemiErrno;
     SemiErrno semiErrno;

   protected: // File IO
     /**
      * Internal state for open files
      *
      * This class describes the internal state of a file opened
      * through the semihosting interface.
      *
      * A file instance is normally created using one of the
      * ArmSemihosting::FileBase::create() factory methods. These
      * methods handle some the magic file names in the Arm Semihosting
      * specification and instantiate the right implementation. For the
      * same, when unserializing a checkpoint, the create method must
      * be used to unserialize a new instance of a file descriptor.
      */
     class FileBase : public Serializable
     {
       public:
         FileBase(ArmSemihosting &_parent, const char *name, const char *_mode)
             : parent(_parent), _name(name), mode(_mode) {}
         virtual ~FileBase() {};

         FileBase() = delete;
         FileBase(FileBase &) = delete;

         static std::unique_ptr<FileBase> create(
             ArmSemihosting &parent, const std::string &fname,
             const char *mode);
         static std::unique_ptr<FileBase> create(
             ArmSemihosting &parent, CheckpointIn &cp, const std::string &sec);

         void serialize(CheckpointOut &cp) const override;
         void unserialize(CheckpointIn &cp) override;

         const std::string &fileName() { return _name; }

       public:
         /** @{
          * Semihosting file IO interfaces
          *
          * These interfaces implement common IO functionality in the
          * Semihosting interface.
          *
          * All functions return a negative value that corresponds to a
          * UNIX errno value when they fail and >=0 on success.
          */

         /**
          * Open the the file.
          *
          * @return <0 on error (-errno), 0 on success.
          */
         virtual int64_t open() { return 0; }

         /**
          * Close the file.
          *
          * @return <0 on error (-errno), 0 on success.
          */
         virtual int64_t close() { return 0; }

         /**
          * Check if a file corresponds to a TTY device.
          *
          * @return True if the file is a TTY, false otherwise.
          */
         virtual bool isTTY() const { return false; }

         /**
          * Read data from file.
          *
          * @return <0 on error (-errno), bytes read on success (0 for EOF).
          */
         virtual int64_t read(uint8_t *buffer, uint64_t size);

         /**
          * Write data to file.
          *
          * @return <0 on error (-errno), bytes written on success.
          */
         virtual int64_t write(const uint8_t *buffer, uint64_t size);

         /**
          * Seek to an absolute position in the file.
          *
          * @param pos Byte offset from start of file.
          * @return <0 on error (-errno), 0 on success.
          */
         virtual int64_t seek(uint64_t pos);

         /**
          * Get the length of a file in bytes.
          *
          * @return <0 on error (-errno), length on success
          */
         virtual int64_t flen();

         /** @} */

       protected:
         ArmSemihosting &parent;
         std::string _name;
         std::string mode;
     };

     /** Implementation of the ':semihosting-features' magic file. */
     class FileFeatures : public FileBase
     {
       public:
         FileFeatures(ArmSemihosting &_parent,
                      const char *name, const char *mode);

         void serialize(CheckpointOut &cp) const override;
         void unserialize(CheckpointIn &cp) override;

         int64_t read(uint8_t *buffer, uint64_t size) override;
         int64_t seek(uint64_t pos) override;

       protected:
         size_t pos;
     };

     class File : public FileBase
     {
       public:
         File(ArmSemihosting &_parent, const char *name, const char *mode);
         ~File();

         void serialize(CheckpointOut &cp) const override;
         void unserialize(CheckpointIn &cp) override;

         int64_t open() override { return openImpl(false); }
         int64_t close() override;
         bool isTTY() const override;
         int64_t read(uint8_t *buffer, uint64_t size) override;
         int64_t write(const uint8_t *buffer, uint64_t size) override;
         int64_t seek(uint64_t pos) override;
         int64_t flen() override;

       protected:
         int64_t openImpl(bool unserialize);
         bool needClose() const { return !isTTY(); }

         FILE *file;
     };

     std::string filesRootDir;
     std::vector<std::unique_ptr<FileBase>> files;
     using Handle = size_t;
     FILE *stdin;
     FILE *stdout;
     FILE *stderr;

   protected: // Helper functions
     unsigned
     calcTickShift() const
     {
         int msb = findMsbSet(SimClock::Frequency);
         return msb > 31 ? msb - 31 : 0;
     }
     uint64_t
     semiTick(Tick tick) const
     {
         return tick >> tickShift;
     }
     void semiExit(uint64_t code, uint64_t subcode);
     std::string readString(ThreadContext *tc, Addr ptr, size_t len);

   public:
     typedef std::pair<uint64_t, SemiErrno> RetErrno;

   private:
     static RetErrno
     retError(SemiErrno e)
     {
         return RetErrno((uint64_t)-1, e);
     }

     static RetErrno
     retOK(uint64_t r)
     {
         return RetErrno(r, 0);
     }

     /**
      * Semihosting call information structure.
      *
      * This structure describes how a semi-hosting call is
      * implemented. It contains debug information (e.g., the name of
      * the call), and a way to invoke it in a particular context.
      */
     struct SemiCall
     {
         /** Call name */
         const char *name;

         // A type for member functions implementing semihosting calls.
         template <typename ...Args>
         using Implementation =
             RetErrno (ArmSemihosting::*)(ThreadContext *tc, Args... args);

         // Since guest ABI doesn't know how to call member function pointers,
         // this template builds a wrapper that takes care of that.
         template <typename ...Args>
         static inline std::function<RetErrno(ThreadContext *tc, Args... args)>
         wrapImpl(ArmSemihosting *sh, Implementation<Args...> impl)
         {
             return [sh, impl](ThreadContext *tc, Args... args) {
                 return (sh->*impl)(tc, args...);
             };
         }

         // A type for functions which dispatch semihosting calls through the
         // guest ABI mechanism.
         using Dispatcher =
             std::function<RetErrno(ArmSemihosting *sh, ThreadContext *tc)>;
         using Dumper = std::function<std::string(ThreadContext *tc)>;

         // Dispatchers for 32 and 64 bits.
         Dispatcher call32;
         Dispatcher call64;

         // Dumpers which print semihosting calls and their arguments.
         Dumper dump32;
         Dumper dump64;

         // A function which builds a dispatcher for a semihosting call.
         template <typename Abi, typename ...Args>
         static inline Dispatcher
         buildDispatcher(Implementation<Args...> impl)
         {
             // This lambda is the dispatcher we're building.
             return [impl](ArmSemihosting *sh, ThreadContext *tc) {
                 auto wrapper = wrapImpl(sh, impl);
                 return invokeSimcall<Abi>(tc, wrapper);
             };
         }

         // A function which builds a dumper for a semihosting call.
         template <typename Abi, typename ...Args>
         static inline Dumper
         buildDumper(const char *name, Implementation<Args...> impl)
         {
             // This lambda is the dumper we're building.
             return [name](ThreadContext *tc) -> std::string {
                 return dumpSimcall<Abi, RetErrno, Args...>(name, tc);
             };
         }

         // When there's one implementation, use it for both 32 and 64 bits.
         template <typename ...Args>
         SemiCall(const char *_name, Implementation<Args...> common) :
             name(_name), call32(buildDispatcher<Abi32>(common)),
             call64(buildDispatcher<Abi64>(common)),
             dump32(buildDumper<Abi32>(_name, common)),
             dump64(buildDumper<Abi64>(_name, common))
         {}

         // When there are two, use one for 32 bits and one for 64 bits.
         template <typename ...Args32, typename ...Args64>
         SemiCall(const char *_name, Implementation<Args32...> impl32,
                  Implementation<Args64...> impl64) :
             name(_name), call32(buildDispatcher<Abi32>(impl32)),
             call64(buildDispatcher<Abi64>(impl64)),
             dump32(buildDumper<Abi32>(_name, impl32)),
             dump64(buildDumper<Abi64>(_name, impl64))
         {}
     };

     RetErrno callOpen(ThreadContext *tc, const Addr name_base,
                       int fmode, size_t name_size);
     RetErrno callClose(ThreadContext *tc, Handle handle);
     RetErrno callWriteC(ThreadContext *tc, InPlaceArg c);
     RetErrno callWrite0(ThreadContext *tc, InPlaceArg str);
     RetErrno callWrite(ThreadContext *tc, Handle handle,
                        Addr buffer, size_t size);
     RetErrno callRead(ThreadContext *tc, Handle handle,
                       Addr buffer, size_t size);
     RetErrno callReadC(ThreadContext *tc);
     RetErrno callIsError(ThreadContext *tc, int64_t status);
     RetErrno callIsTTY(ThreadContext *tc, Handle handle);
     RetErrno callSeek(ThreadContext *tc, Handle handle, uint64_t pos);
     RetErrno callFLen(ThreadContext *tc, Handle handle);
     RetErrno callTmpNam(ThreadContext *tc, Addr buffer,
                         uint64_t id, size_t size);
     RetErrno callRemove(ThreadContext *tc, Addr name_base, size_t name_size);
     RetErrno callRename(ThreadContext *tc, Addr from_addr, size_t from_size,
                         Addr to_addr, size_t to_size);
     RetErrno callClock(ThreadContext *tc);
     RetErrno callTime(ThreadContext *tc);
     RetErrno callSystem(ThreadContext *tc, Addr cmd_addr, size_t cmd_size);
     RetErrno callErrno(ThreadContext *tc);
     RetErrno callGetCmdLine(ThreadContext *tc, Addr addr, InPlaceArg size_arg);

     void gatherHeapInfo(ThreadContext *tc, bool aarch64,
                         Addr &heap_base, Addr &heap_limit,
                         Addr &stack_base, Addr &stack_limit);
     RetErrno callHeapInfo32(ThreadContext *tc, Addr block_addr);
     RetErrno callHeapInfo64(ThreadContext *tc, Addr block_addr);
     RetErrno callExit32(ThreadContext *tc, InPlaceArg code);
     RetErrno callExit64(ThreadContext *tc, uint64_t code, uint64_t subcode);
     RetErrno callExitExtended(ThreadContext *tc, uint64_t code,
                               uint64_t subcode);

     RetErrno callElapsed32(ThreadContext *tc, InPlaceArg low, InPlaceArg high);
     RetErrno callElapsed64(ThreadContext *tc, InPlaceArg ticks);
     RetErrno callTickFreq(ThreadContext *tc);

     RetErrno callGem5PseudoOp32(ThreadContext *tc, uint32_t encoded_func);
     RetErrno callGem5PseudoOp64(ThreadContext *tc, uint64_t encoded_func);

     template <typename Abi>
     void
     unrecognizedCall(ThreadContext *tc, const char *format, uint64_t op)
     {
         warn(format, op);
         std::function<RetErrno(ThreadContext *tc)> retErr =
             [](ThreadContext *tc) { return retError(EINVAL); };
         invokeSimcall<Abi>(tc, retErr);
     }

     static FILE *getSTDIO(const char *stream_name,
                           const std::string &name, const char *mode);

     static const std::map<uint32_t, SemiCall> calls;
     static const std::vector<const char *> fmodes;
     static const std::map<uint64_t, const char *> exitCodes;
     static const std::vector<uint8_t> features;
     static const std::map<const std::string, FILE *> stdioMap;
 };

 std::ostream &operator << (
         std::ostream &os, const ArmSemihosting::InPlaceArg &ipa);

 namespace GuestABI
 {

 template <typename Arg>
 struct Argument<ArmSemihosting::Abi64, Arg,
     typename std::enable_if<std::is_integral<Arg>::value>::type>
 {
     static Arg
     get(ThreadContext *tc, ArmSemihosting::Abi64::State &state)
     {
         return state.get(tc);
     }
 };

 template <typename Arg>
 struct Argument<ArmSemihosting::Abi32, Arg,
     typename std::enable_if<std::is_integral<Arg>::value>::type>
 {
     static Arg
     get(ThreadContext *tc, ArmSemihosting::Abi32::State &state)
     {
         if (std::is_signed<Arg>::value)
             return sext<32>(state.get(tc));
         else
             return state.get(tc);
     }
 };

 template <typename Abi>
 struct Argument<Abi, ArmSemihosting::InPlaceArg, typename std::enable_if<
     std::is_base_of<ArmSemihosting::AbiBase, Abi>::value>::type>
 {
     static ArmSemihosting::InPlaceArg
     get(ThreadContext *tc, typename Abi::State &state)
     {
         return ArmSemihosting::InPlaceArg(
                 state.getAddr(), sizeof(typename Abi::State::ArgType));
     }
 };

 template <>
 struct Result<ArmSemihosting::Abi32, ArmSemihosting::RetErrno>
 {
     static void
     store(ThreadContext *tc, const ArmSemihosting::RetErrno &err)
     {
         tc->setIntReg(ArmISA::INTREG_R0, err.first);
     }
 };

 template <>
 struct Result<ArmSemihosting::Abi64, ArmSemihosting::RetErrno>
 {
     static void
     store(ThreadContext *tc, const ArmSemihosting::RetErrno &err)
     {
         tc->setIntReg(ArmISA::INTREG_X0, err.first);
     }
 };

 } // namespace GuestABI

 #endif // __ARCH_ARM_SEMIHOSTING_HH__
	/*
	* Copyright (c) 2018, 2019 ARM Limited
	* All rights reserved
	*
	* The license below extends only to copyright in the software and shall
	* not be construed as granting a license to any other intellectual
	* property including but not limited to intellectual property relating
	* to a hardware implementation of the functionality of the software
	* licensed hereunder. You may use the software subject to the license
	* terms below provided that you ensure that this notice is replicated
	* unmodified and in its entirety in all distributions of the software,
	* modified or unmodified, in source code or in binary form.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions are
	* met: redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer;
	* redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution;
	* neither the name of the copyright holders nor the names of its
	* contributors may be used to endorse or promote products derived from
	* this software without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#ifndef __ARCH_ARM_SEMIHOSTING_HH__
	#define __ARCH_ARM_SEMIHOSTING_HH__

	#include <cstdio>
	#include <functional>
	#include <map>
	#include <memory>
	#include <utility>
	#include <vector>

	#include "arch/arm/intregs.hh"
	#include "arch/arm/utility.hh"
	#include "cpu/thread_context.hh"
	#include "mem/port_proxy.hh"
	#include "sim/guest_abi.hh"
	#include "sim/sim_object.hh"

	struct ArmSemihostingParams;
	class SerialDevice;

	/**
	* Semihosting for AArch32 and AArch64
	*
	* This class implements the Arm semihosting interface. This interface
	* allows baremetal code access service, such as IO, from the
	* simulator. It is conceptually a simplified version of gem5's more
	* general syscall emulation mode.
	*
	* Exits calls (SYS_EXIT, SYS_EXIT_EXTENDED) from the guest get
	* translated into simualtion exits. Well-known exit codes are
	* translated to messages on the form 'semi:ADP_.*' while unknown
	* codes are returned in hex ('semi:0x..'). The subcode is reported in
	* the gem5 exit event.
	*/
	class ArmSemihosting : public SimObject
	{
	public:

	enum {
	// Standard ARM immediate values which trigger semihosting.
	T32Imm = 0xAB,
	A32Imm = 0x123456,
	A64Imm = 0xF000,

	// The immediate value which enables gem5 semihosting calls. Use the
	// standard value for thumb.
	Gem5Imm = 0x5D57
	};

	static PortProxy &portProxy(ThreadContext *tc);

	struct AbiBase
	{
	template <typename Arg>
	class StateBase
	{
	private:
	Addr argPointer;
	ByteOrder endian;

	public:
	StateBase(const ThreadContext *tc, Addr arg_pointer) :
	argPointer(arg_pointer), endian(ArmISA::byteOrder(tc))
	{}

	/*
	* These two methods are used to both read an argument or its
	* address, and to move position on to the next location. Normally
	* State would be more passive, but since it behaves almost the
	* same no matter what the argument type is we can simplify and
	* consolidate a little bit by centralizing these methods.
	*/

	// Return the address of an argument slot and move past it.
	Addr
	getAddr()
	{
	Addr addr = argPointer;
	argPointer += sizeof(Arg);
	return addr;
	}

	// Read the value in an argument slot and move past it.
	Arg
	get(ThreadContext *tc)
	{
	Arg arg = ArmSemihosting::portProxy(tc).read<Arg>(
	argPointer, endian);
	argPointer += sizeof(Arg);
	return arg;
	}

	using ArgType = Arg;
	};
	};

	struct Abi64 : public AbiBase
	{
	class State : public StateBase<uint64_t>
	{
	public:
	// For 64 bit semihosting, the params are pointer to by X1.
	explicit State(const ThreadContext *tc) :
	StateBase<uint64_t>(tc, tc->readIntReg(ArmISA::INTREG_X1))
	{}
	};
	};

	struct Abi32 : public AbiBase
	{
	class State : public StateBase<uint64_t>
	{
	public:
	// For 32 bit semihosting, the params are pointer to by R1.
	explicit State(const ThreadContext *tc) :
	StateBase<uint64_t>(tc, tc->readIntReg(ArmISA::INTREG_R1))
	{}
	};
	};

	// Use this argument type when you need to modify an argument in place.
	// This will give you the address of the argument itself and the size of
	// each argument slot, rather than the actual value of the argument.
	struct InPlaceArg
	{
	Addr addr;
	size_t size;

	InPlaceArg(Addr _addr, size_t _size) : addr(_addr), size(_size) {}

	// A helper function to read the argument since the guest ABI mechanism
	// didn't do that for us.
	uint64_t
	read(ThreadContext *tc, ByteOrder endian)
	{
	auto &proxy = ArmSemihosting::portProxy(tc);
	if (size == 8)
	return proxy.read<uint64_t>(addr, endian);
	else if (size == 4)
	return proxy.read<uint32_t>(addr, endian);
	else
	panic("Unexpected semihosting argument size %d.", size);
	}

	// A helper function to write to the argument's slot in the params.
	void
	write(ThreadContext *tc, uint64_t val, ByteOrder endian)
	{
	auto &proxy = ArmSemihosting::portProxy(tc);
	if (size == 8)
	proxy.write<uint64_t>(addr, val, endian);
	else if (size == 4)
	proxy.write<uint32_t>(addr, val, endian);
	else
	panic("Unexpected semihosting argument size %d.", size);
	}
	};

	enum Operation {
	SYS_OPEN = 0x01,
	SYS_CLOSE = 0x02,
	SYS_WRITEC = 0x03,
	SYS_WRITE0 = 0x04,
	SYS_WRITE = 0x05,
	SYS_READ = 0x06,
	SYS_READC = 0x07,
	SYS_ISERROR = 0x08,
	SYS_ISTTY = 0x09,
	SYS_SEEK = 0x0A,
	SYS_FLEN = 0x0C,
	SYS_TMPNAM = 0x0D,
	SYS_REMOVE = 0x0E,
	SYS_RENAME = 0x0F,
	SYS_CLOCK = 0x10,
	SYS_TIME = 0x11,
	SYS_SYSTEM = 0x12,
	SYS_ERRNO = 0x13,
	SYS_GET_CMDLINE = 0x15,
	SYS_HEAPINFO = 0x16,
	SYS_EXIT = 0x18,
	SYS_EXIT_EXTENDED = 0x20,
	SYS_ELAPSED = 0x30,
	SYS_TICKFREQ = 0x31,

	MaxStandardOp = 0xFF,

	SYS_GEM5_PSEUDO_OP = 0x100
	};

	ArmSemihosting(const ArmSemihostingParams *p);

	/** Perform an Arm Semihosting call from aarch64 code. */
	bool call64(ThreadContext *tc, bool gem5_ops);
	/** Perform an Arm Semihosting call from aarch32 code. */
	bool call32(ThreadContext *tc, bool gem5_ops);

	public: // SimObject and related interfaces
	void serialize(CheckpointOut &cp) const override;
	void unserialize(CheckpointIn &cp) override;

	protected: // Configuration
	const std::string cmdLine;
	const Addr memReserve;
	const Addr stackSize;

	/**
	* Base time when the simulation started. This is used to
	* calculate the time of date when the guest call SYS_TIME.
	*/
	const time_t timeBase;

	/** Number of bits to right shift gem5 ticks to fit in a uint32_t */
	const unsigned tickShift;

	protected: // Internal state
	typedef uint64_t SemiErrno;
	SemiErrno semiErrno;

	protected: // File IO
	/**
	* Internal state for open files
	*
	* This class describes the internal state of a file opened
	* through the semihosting interface.
	*
	* A file instance is normally created using one of the
	* ArmSemihosting::FileBase::create() factory methods. These
	* methods handle some the magic file names in the Arm Semihosting
	* specification and instantiate the right implementation. For the
	* same, when unserializing a checkpoint, the create method must
	* be used to unserialize a new instance of a file descriptor.
	*/
	class FileBase : public Serializable
	{
	public:
	FileBase(ArmSemihosting &_parent, const char name, const char _mode)
	: parent(_parent), _name(name), mode(_mode) {}
	virtual ~FileBase() {};

	FileBase() = delete;
	FileBase(FileBase &) = delete;

	static std::unique_ptr<FileBase> create(
	ArmSemihosting &parent, const std::string &fname,
	const char *mode);
	static std::unique_ptr<FileBase> create(
	ArmSemihosting &parent, CheckpointIn &cp, const std::string &sec);

	void serialize(CheckpointOut &cp) const override;
	void unserialize(CheckpointIn &cp) override;

	const std::string &fileName() { return _name; }

	public:
	/** @{
	* Semihosting file IO interfaces
	*
	* These interfaces implement common IO functionality in the
	* Semihosting interface.
	*
	* All functions return a negative value that corresponds to a
	* UNIX errno value when they fail and >=0 on success.
	*/

	/**
	* Open the the file.
	*
	* @return <0 on error (-errno), 0 on success.
	*/
	virtual int64_t open() { return 0; }

	/**
	* Close the file.
	*
	* @return <0 on error (-errno), 0 on success.
	*/
	virtual int64_t close() { return 0; }

	/**
	* Check if a file corresponds to a TTY device.
	*
	* @return True if the file is a TTY, false otherwise.
	*/
	virtual bool isTTY() const { return false; }

	/**
	* Read data from file.
	*
	* @return <0 on error (-errno), bytes read on success (0 for EOF).
	*/
	virtual int64_t read(uint8_t *buffer, uint64_t size);

	/**
	* Write data to file.
	*
	* @return <0 on error (-errno), bytes written on success.
	*/
	virtual int64_t write(const uint8_t *buffer, uint64_t size);

	/**
	* Seek to an absolute position in the file.
	*
	* @param pos Byte offset from start of file.
	* @return <0 on error (-errno), 0 on success.
	*/
	virtual int64_t seek(uint64_t pos);

	/**
	* Get the length of a file in bytes.
	*
	* @return <0 on error (-errno), length on success
	*/
	virtual int64_t flen();

	/** @} */

	protected:
	ArmSemihosting &parent;
	std::string _name;
	std::string mode;
	};

	/** Implementation of the ':semihosting-features' magic file. */
	class FileFeatures : public FileBase
	{
	public:
	FileFeatures(ArmSemihosting &_parent,
	const char name, const char mode);

	void serialize(CheckpointOut &cp) const override;
	void unserialize(CheckpointIn &cp) override;

	int64_t read(uint8_t *buffer, uint64_t size) override;
	int64_t seek(uint64_t pos) override;

	protected:
	size_t pos;
	};

	class File : public FileBase
	{
	public:
	File(ArmSemihosting &_parent, const char name, const char mode);
	~File();

	void serialize(CheckpointOut &cp) const override;
	void unserialize(CheckpointIn &cp) override;

	int64_t open() override { return openImpl(false); }
	int64_t close() override;
	bool isTTY() const override;
	int64_t read(uint8_t *buffer, uint64_t size) override;
	int64_t write(const uint8_t *buffer, uint64_t size) override;
	int64_t seek(uint64_t pos) override;
	int64_t flen() override;

	protected:
	int64_t openImpl(bool unserialize);
	bool needClose() const { return !isTTY(); }

	FILE *file;
	};

	std::string filesRootDir;
	std::vector<std::unique_ptr<FileBase>> files;
	using Handle = size_t;
	FILE *stdin;
	FILE *stdout;
	FILE *stderr;

	protected: // Helper functions
	unsigned
	calcTickShift() const
	{
	int msb = findMsbSet(SimClock::Frequency);
	return msb > 31 ? msb - 31 : 0;
	}
	uint64_t
	semiTick(Tick tick) const
	{
	return tick >> tickShift;
	}
	void semiExit(uint64_t code, uint64_t subcode);
	std::string readString(ThreadContext *tc, Addr ptr, size_t len);

	public:
	typedef std::pair<uint64_t, SemiErrno> RetErrno;

	private:
	static RetErrno
	retError(SemiErrno e)
	{
	return RetErrno((uint64_t)-1, e);
	}

	static RetErrno
	retOK(uint64_t r)
	{
	return RetErrno(r, 0);
	}

	/**
	* Semihosting call information structure.
	*
	* This structure describes how a semi-hosting call is
	* implemented. It contains debug information (e.g., the name of
	* the call), and a way to invoke it in a particular context.
	*/
	struct SemiCall
	{
	/** Call name */
	const char *name;

	// A type for member functions implementing semihosting calls.
	template <typename ...Args>
	using Implementation =
	RetErrno (ArmSemihosting::)(ThreadContext tc, Args... args);

	// Since guest ABI doesn't know how to call member function pointers,
	// this template builds a wrapper that takes care of that.
	template <typename ...Args>
	static inline std::function<RetErrno(ThreadContext *tc, Args... args)>
	wrapImpl(ArmSemihosting *sh, Implementation<Args...> impl)
	{
	return [sh, impl](ThreadContext *tc, Args... args) {
	return (sh->*impl)(tc, args...);
	};
	}

	// A type for functions which dispatch semihosting calls through the
	// guest ABI mechanism.
	using Dispatcher =
	std::function<RetErrno(ArmSemihosting sh, ThreadContext tc)>;
	using Dumper = std::function<std::string(ThreadContext *tc)>;

	// Dispatchers for 32 and 64 bits.
	Dispatcher call32;
	Dispatcher call64;

	// Dumpers which print semihosting calls and their arguments.
	Dumper dump32;
	Dumper dump64;

	// A function which builds a dispatcher for a semihosting call.
	template <typename Abi, typename ...Args>
	static inline Dispatcher
	buildDispatcher(Implementation<Args...> impl)
	{
	// This lambda is the dispatcher we're building.
	return [impl](ArmSemihosting sh, ThreadContext tc) {
	auto wrapper = wrapImpl(sh, impl);
	return invokeSimcall<Abi>(tc, wrapper);
	};
	}

	// A function which builds a dumper for a semihosting call.
	template <typename Abi, typename ...Args>
	static inline Dumper
	buildDumper(const char *name, Implementation<Args...> impl)
	{
	// This lambda is the dumper we're building.
	return [name](ThreadContext *tc) -> std::string {
	return dumpSimcall<Abi, RetErrno, Args...>(name, tc);
	};
	}

	// When there's one implementation, use it for both 32 and 64 bits.
	template <typename ...Args>
	SemiCall(const char *_name, Implementation<Args...> common) :
	name(_name), call32(buildDispatcher<Abi32>(common)),
	call64(buildDispatcher<Abi64>(common)),
	dump32(buildDumper<Abi32>(_name, common)),
	dump64(buildDumper<Abi64>(_name, common))
	{}

	// When there are two, use one for 32 bits and one for 64 bits.
	template <typename ...Args32, typename ...Args64>
	SemiCall(const char *_name, Implementation<Args32...> impl32,
	Implementation<Args64...> impl64) :
	name(_name), call32(buildDispatcher<Abi32>(impl32)),
	call64(buildDispatcher<Abi64>(impl64)),
	dump32(buildDumper<Abi32>(_name, impl32)),
	dump64(buildDumper<Abi64>(_name, impl64))
	{}
	};

	RetErrno callOpen(ThreadContext *tc, const Addr name_base,
	int fmode, size_t name_size);
	RetErrno callClose(ThreadContext *tc, Handle handle);
	RetErrno callWriteC(ThreadContext *tc, InPlaceArg c);
	RetErrno callWrite0(ThreadContext *tc, InPlaceArg str);
	RetErrno callWrite(ThreadContext *tc, Handle handle,
	Addr buffer, size_t size);
	RetErrno callRead(ThreadContext *tc, Handle handle,
	Addr buffer, size_t size);
	RetErrno callReadC(ThreadContext *tc);
	RetErrno callIsError(ThreadContext *tc, int64_t status);
	RetErrno callIsTTY(ThreadContext *tc, Handle handle);
	RetErrno callSeek(ThreadContext *tc, Handle handle, uint64_t pos);
	RetErrno callFLen(ThreadContext *tc, Handle handle);
	RetErrno callTmpNam(ThreadContext *tc, Addr buffer,
	uint64_t id, size_t size);
	RetErrno callRemove(ThreadContext *tc, Addr name_base, size_t name_size);
	RetErrno callRename(ThreadContext *tc, Addr from_addr, size_t from_size,
	Addr to_addr, size_t to_size);
	RetErrno callClock(ThreadContext *tc);
	RetErrno callTime(ThreadContext *tc);
	RetErrno callSystem(ThreadContext *tc, Addr cmd_addr, size_t cmd_size);
	RetErrno callErrno(ThreadContext *tc);
	RetErrno callGetCmdLine(ThreadContext *tc, Addr addr, InPlaceArg size_arg);

	void gatherHeapInfo(ThreadContext *tc, bool aarch64,
	Addr &heap_base, Addr &heap_limit,
	Addr &stack_base, Addr &stack_limit);
	RetErrno callHeapInfo32(ThreadContext *tc, Addr block_addr);
	RetErrno callHeapInfo64(ThreadContext *tc, Addr block_addr);
	RetErrno callExit32(ThreadContext *tc, InPlaceArg code);
	RetErrno callExit64(ThreadContext *tc, uint64_t code, uint64_t subcode);
	RetErrno callExitExtended(ThreadContext *tc, uint64_t code,
	uint64_t subcode);

	RetErrno callElapsed32(ThreadContext *tc, InPlaceArg low, InPlaceArg high);
	RetErrno callElapsed64(ThreadContext *tc, InPlaceArg ticks);
	RetErrno callTickFreq(ThreadContext *tc);

	RetErrno callGem5PseudoOp32(ThreadContext *tc, uint32_t encoded_func);
	RetErrno callGem5PseudoOp64(ThreadContext *tc, uint64_t encoded_func);

	template <typename Abi>
	void
	unrecognizedCall(ThreadContext tc, const char format, uint64_t op)
	{
	warn(format, op);
	std::function<RetErrno(ThreadContext *tc)> retErr =
	[](ThreadContext *tc) { return retError(EINVAL); };
	invokeSimcall<Abi>(tc, retErr);
	}

	static FILE getSTDIO(const char stream_name,
	const std::string &name, const char *mode);

	static const std::map<uint32_t, SemiCall> calls;
	static const std::vector<const char *> fmodes;
	static const std::map<uint64_t, const char *> exitCodes;
	static const std::vector<uint8_t> features;
	static const std::map<const std::string, FILE *> stdioMap;
	};

	std::ostream &operator << (
	std::ostream &os, const ArmSemihosting::InPlaceArg &ipa);

	namespace GuestABI
	{

	template <typename Arg>
	struct Argument<ArmSemihosting::Abi64, Arg,
	typename std::enable_if<std::is_integral<Arg>::value>::type>
	{
	static Arg
	get(ThreadContext *tc, ArmSemihosting::Abi64::State &state)
	{
	return state.get(tc);
	}
	};

	template <typename Arg>
	struct Argument<ArmSemihosting::Abi32, Arg,
	typename std::enable_if<std::is_integral<Arg>::value>::type>
	{
	static Arg
	get(ThreadContext *tc, ArmSemihosting::Abi32::State &state)
	{
	if (std::is_signed<Arg>::value)
	return sext<32>(state.get(tc));
	else
	return state.get(tc);
	}
	};

	template <typename Abi>
	struct Argument<Abi, ArmSemihosting::InPlaceArg, typename std::enable_if<
	std::is_base_of<ArmSemihosting::AbiBase, Abi>::value>::type>
	{
	static ArmSemihosting::InPlaceArg
	get(ThreadContext *tc, typename Abi::State &state)
	{
	return ArmSemihosting::InPlaceArg(
	state.getAddr(), sizeof(typename Abi::State::ArgType));
	}
	};

	template <>
	struct Result<ArmSemihosting::Abi32, ArmSemihosting::RetErrno>
	{
	static void
	store(ThreadContext *tc, const ArmSemihosting::RetErrno &err)
	{
	tc->setIntReg(ArmISA::INTREG_R0, err.first);
	}
	};

	template <>
	struct Result<ArmSemihosting::Abi64, ArmSemihosting::RetErrno>
	{
	static void
	store(ThreadContext *tc, const ArmSemihosting::RetErrno &err)
	{
	tc->setIntReg(ArmISA::INTREG_X0, err.first);
	}
	};

	} // namespace GuestABI

	#endif // __ARCH_ARM_SEMIHOSTING_HH__