src/sim/process.cc - public/gem5 - Git at Google

 /*
  * Copyright (c) 2014-2016 Advanced Micro Devices, Inc.
  * Copyright (c) 2012 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.
  *
  * Copyright (c) 2001-2005 The Regents of The University of Michigan
  * All rights reserved.
  *
  * 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.
  */

 #include "sim/process.hh"

 #include <fcntl.h>
 #include <unistd.h>

 #include <array>
 #include <climits>
 #include <csignal>
 #include <map>
 #include <string>
 #include <vector>

 #include "base/intmath.hh"
 #include "base/loader/object_file.hh"
 #include "base/loader/symtab.hh"
 #include "base/statistics.hh"
 #include "cpu/thread_context.hh"
 #include "mem/page_table.hh"
 #include "mem/se_translating_port_proxy.hh"
 #include "params/Process.hh"
 #include "sim/emul_driver.hh"
 #include "sim/fd_array.hh"
 #include "sim/fd_entry.hh"
 #include "sim/redirect_path.hh"
 #include "sim/se_workload.hh"
 #include "sim/syscall_desc.hh"
 #include "sim/system.hh"

 namespace gem5
 {

 namespace
 {

 typedef std::vector<Process::Loader *> LoaderList;

 LoaderList &
 process_loaders()
 {
     static LoaderList loaders;
     return loaders;
 }

 } // anonymous namespace

 Process::Loader::Loader()
 {
     process_loaders().emplace_back(this);
 }

 Process *
 Process::tryLoaders(const ProcessParams &params,
                     loader::ObjectFile *obj_file)
 {
     for (auto &loader_it : process_loaders()) {
         Process *p = loader_it->load(params, obj_file);
         if (p)
             return p;
     }

     return nullptr;
 }

 static std::string
 normalize(const std::string& directory)
 {
     if (directory.back() != '/')
         return directory + '/';
     return directory;
 }

 Process::Process(const ProcessParams &params, EmulationPageTable *pTable,
                  loader::ObjectFile *obj_file)
     : SimObject(params), system(params.system),
       seWorkload(dynamic_cast<SEWorkload *>(system->workload)),
       useArchPT(params.useArchPT),
       kvmInSE(params.kvmInSE),
       useForClone(false),
       pTable(pTable),
       objFile(obj_file),
       argv(params.cmd), envp(params.env),
       executable(params.executable == "" ? params.cmd[0] : params.executable),
       tgtCwd(normalize(params.cwd)),
       hostCwd(checkPathRedirect(tgtCwd)),
       release(params.release),
       _uid(params.uid), _euid(params.euid),
       _gid(params.gid), _egid(params.egid),
       _pid(params.pid), _ppid(params.ppid),
       _pgid(params.pgid), drivers(params.drivers),
       fds(std::make_shared<FDArray>(
                   params.input, params.output, params.errout)),
       childClearTID(0),
       ADD_STAT(numSyscalls, statistics::units::Count::get(),
                "Number of system calls")
 {
     fatal_if(!seWorkload, "Couldn't find appropriate workload object.");
     fatal_if(_pid >= System::maxPID, "_pid is too large: %d", _pid);

     auto ret_pair = system->PIDs.emplace(_pid);
     fatal_if(!ret_pair.second, "_pid %d is already used", _pid);

     /**
      * Linux bundles together processes into this concept called a thread
      * group. The thread group is responsible for recording which processes
      * behave as threads within a process context. The thread group leader
      * is the process who's tgid is equal to its pid. Other processes which
      * belong to the thread group, but do not lead the thread group, are
      * treated as child threads. These threads are created by the clone system
      * call with options specified to create threads (differing from the
      * options used to implement a fork). By default, set up the tgid/pid
      * with a new, equivalent value. If CLONE_THREAD is specified, patch
      * the tgid value with the old process' value.
      */
     _tgid = params.pid;

     exitGroup = new bool();
     sigchld = new bool();

     image = objFile->buildImage();

     if (loader::debugSymbolTable.empty())
         loader::debugSymbolTable = objFile->symtab();
 }

 void
 Process::clone(ThreadContext *otc, ThreadContext *ntc,
                Process *np, RegVal flags)
 {
 #ifndef CLONE_VM
 #define CLONE_VM 0
 #endif
 #ifndef CLONE_FILES
 #define CLONE_FILES 0
 #endif
 #ifndef CLONE_THREAD
 #define CLONE_THREAD 0
 #endif
 #ifndef CLONE_VFORK
 #define CLONE_VFORK 0
 #endif
     if (CLONE_VM & flags) {
         /**
          * Share the process memory address space between the new process
          * and the old process. Changes in one will be visible in the other
          * due to the pointer use.
          */
         delete np->pTable;
         np->pTable = pTable;

         np->memState = memState;
     } else {
         /**
          * Duplicate the process memory address space. The state needs to be
          * copied over (rather than using pointers to share everything).
          */
         typedef std::vector<std::pair<Addr,Addr>> MapVec;
         MapVec mappings;
         pTable->getMappings(&mappings);

         for (auto map : mappings) {
             Addr paddr, vaddr = map.first;
             bool alloc_page = !(np->pTable->translate(vaddr, paddr));
             np->replicatePage(vaddr, paddr, otc, ntc, alloc_page);
         }

         *np->memState = *memState;
     }

     if (CLONE_FILES & flags) {
         /**
          * The parent and child file descriptors are shared because the
          * two FDArray pointers are pointing to the same FDArray. Opening
          * and closing file descriptors will be visible to both processes.
          */
         np->fds = fds;
     } else {
         /**
          * Copy the file descriptors from the old process into the new
          * child process. The file descriptors entry can be opened and
          * closed independently of the other process being considered. The
          * host file descriptors are also dup'd so that the flags for the
          * host file descriptor is independent of the other process.
          */
         std::shared_ptr<FDArray> nfds = np->fds;
         for (int tgt_fd = 0; tgt_fd < fds->getSize(); tgt_fd++) {
             std::shared_ptr<FDEntry> this_fde = (*fds)[tgt_fd];
             if (!this_fde) {
                 nfds->setFDEntry(tgt_fd, nullptr);
                 continue;
             }
             nfds->setFDEntry(tgt_fd, this_fde->clone());

             auto this_hbfd = std::dynamic_pointer_cast<HBFDEntry>(this_fde);
             if (!this_hbfd)
                 continue;

             int this_sim_fd = this_hbfd->getSimFD();
             if (this_sim_fd <= 2)
                 continue;

             int np_sim_fd = dup(this_sim_fd);
             assert(np_sim_fd != -1);

             auto nhbfd = std::dynamic_pointer_cast<HBFDEntry>((*nfds)[tgt_fd]);
             nhbfd->setSimFD(np_sim_fd);
         }
     }

     if (CLONE_THREAD & flags) {
         np->_tgid = _tgid;
         delete np->exitGroup;
         np->exitGroup = exitGroup;
     }

     if (CLONE_VFORK & flags) {
         np->vforkContexts.push_back(otc->contextId());
     }

     np->argv.insert(np->argv.end(), argv.begin(), argv.end());
     np->envp.insert(np->envp.end(), envp.begin(), envp.end());
 }

 void
 Process::revokeThreadContext(int context_id)
 {
     std::vector<ContextID>::iterator it;
     for (it = contextIds.begin(); it != contextIds.end(); it++) {
         if (*it == context_id) {
             contextIds.erase(it);
             return;
         }
     }
     warn("Unable to find thread context to revoke");
 }

 void
 Process::init()
 {
     // Patch the ld_bias for dynamic executables.
     updateBias();

     if (objFile->getInterpreter())
         interpImage = objFile->getInterpreter()->buildImage();
 }

 void
 Process::initState()
 {
     if (contextIds.empty())
         fatal("Process %s is not associated with any HW contexts!\n", name());

     // first thread context for this process... initialize & enable
     ThreadContext *tc = system->threads[contextIds[0]];

     // mark this context as active so it will start ticking.
     tc->activate();

     pTable->initState();

     initVirtMem.reset(new SETranslatingPortProxy(
                 tc, SETranslatingPortProxy::Always));

     // load object file into target memory
     image.write(*initVirtMem);
     interpImage.write(*initVirtMem);
 }

 DrainState
 Process::drain()
 {
     fds->updateFileOffsets();
     return DrainState::Drained;
 }

 void
 Process::allocateMem(Addr vaddr, int64_t size, bool clobber)
 {
     const auto page_size = pTable->pageSize();

     const Addr page_addr = roundDown(vaddr, page_size);

     // Check if the page has been mapped by other cores if not to clobber.
     // When running multithreaded programs in SE-mode with DerivO3CPU model,
     // there are cases where two or more cores have page faults on the same
     // page in nearby ticks. When the cores try to handle the faults at the
     // commit stage (also in nearby ticks/cycles), the first core will ask for
     // a physical page frame to map with the virtual page. Other cores can
     // return if the page has been mapped and `!clobber`.
     if (!clobber) {
         const EmulationPageTable::Entry *pte = pTable->lookup(page_addr);
         if (pte) {
             warn("Process::allocateMem: addr %#x already mapped\n", vaddr);
             return;
         }
     }

     const int npages = divCeil(size, page_size);
     const Addr paddr = seWorkload->allocPhysPages(npages);
     const Addr pages_size = npages * page_size;
     pTable->map(page_addr, paddr, pages_size,
                 clobber ? EmulationPageTable::Clobber :
                           EmulationPageTable::MappingFlags(0));
 }

 void
 Process::replicatePage(Addr vaddr, Addr new_paddr, ThreadContext *old_tc,
                        ThreadContext *new_tc, bool allocate_page)
 {
     if (allocate_page)
         new_paddr = seWorkload->allocPhysPages(1);

     // Read from old physical page.
     uint8_t buf_p[pTable->pageSize()];
     SETranslatingPortProxy(old_tc).readBlob(vaddr, buf_p, sizeof(buf_p));

     // Create new mapping in process address space by clobbering existing
     // mapping (if any existed) and then write to the new physical page.
     bool clobber = true;
     pTable->map(vaddr, new_paddr, sizeof(buf_p), clobber);
     SETranslatingPortProxy(new_tc).writeBlob(vaddr, buf_p, sizeof(buf_p));
 }

 bool
 Process::fixupFault(Addr vaddr)
 {
     return memState->fixupFault(vaddr);
 }

 void
 Process::serialize(CheckpointOut &cp) const
 {
     memState->serialize(cp);
     pTable->serialize(cp);
     fds->serialize(cp);

     /**
      * Checkpoints for pipes, device drivers or sockets currently
      * do not work. Need to come back and fix them at a later date.
      */

     warn("Checkpoints for pipes, device drivers and sockets do not work.");
 }

 void
 Process::unserialize(CheckpointIn &cp)
 {
     memState->unserialize(cp);
     pTable->unserialize(cp);
     fds->unserialize(cp);

     /**
      * Checkpoints for pipes, device drivers or sockets currently
      * do not work. Need to come back and fix them at a later date.
      */
     warn("Checkpoints for pipes, device drivers and sockets do not work.");
     // The above returns a bool so that you could do something if you don't
     // find the param in the checkpoint if you wanted to, like set a default
     // but in this case we'll just stick with the instantiated value if not
     // found.
 }

 bool
 Process::map(Addr vaddr, Addr paddr, int size, bool cacheable)
 {
     pTable->map(vaddr, paddr, size,
                 cacheable ? EmulationPageTable::MappingFlags(0) :
                             EmulationPageTable::Uncacheable);
     return true;
 }

 EmulatedDriver *
 Process::findDriver(std::string filename)
 {
     for (EmulatedDriver *d : drivers) {
         if (d->match(filename))
             return d;
     }

     return nullptr;
 }

 std::string
 Process::checkPathRedirect(const std::string &filename)
 {
     // If the input parameter contains a relative path, convert it.
     // The target version of the current working directory is fine since
     // we immediately convert it using redirect paths into a host version.
     auto abs_path = absolutePath(filename, false);

     for (auto path : system->redirectPaths) {
         // Search through the redirect paths to see if a starting substring of
         // our path falls into any buckets which need to redirected.
         if (startswith(abs_path, path->appPath())) {
             std::string tail = abs_path.substr(path->appPath().size());

             // If this path needs to be redirected, search through a list
             // of targets to see if we can match a valid file (or directory).
             for (auto host_path : path->hostPaths()) {
                 if (access((host_path + tail).c_str(), R_OK) == 0) {
                     // Return the valid match.
                     return host_path + tail;
                 }
             }
             // The path needs to be redirected, but the file or directory
             // does not exist on the host filesystem. Return the first
             // host path as a default.
             return path->hostPaths()[0] + tail;
         }
     }

     // The path does not need to be redirected.
     return abs_path;
 }

 void
 Process::updateBias()
 {
     auto *interp = objFile->getInterpreter();

     if (!interp || !interp->relocatable())
         return;

     // Determine how large the interpreters footprint will be in the process
     // address space.
     Addr interp_mapsize = roundUp(interp->mapSize(), pTable->pageSize());

     // We are allocating the memory area; set the bias to the lowest address
     // in the allocated memory region.
     Addr mmap_end = memState->getMmapEnd();
     Addr ld_bias = mmapGrowsDown() ? mmap_end - interp_mapsize : mmap_end;

     // Adjust the process mmap area to give the interpreter room; the real
     // execve system call would just invoke the kernel's internal mmap
     // functions to make these adjustments.
     mmap_end = mmapGrowsDown() ? ld_bias : mmap_end + interp_mapsize;
     memState->setMmapEnd(mmap_end);

     interp->updateBias(ld_bias);
 }

 loader::ObjectFile *
 Process::getInterpreter()
 {
     return objFile->getInterpreter();
 }

 Addr
 Process::getBias()
 {
     auto *interp = getInterpreter();

     return interp ? interp->bias() : objFile->bias();
 }

 Addr
 Process::getStartPC()
 {
     auto *interp = getInterpreter();

     return interp ? interp->entryPoint() : objFile->entryPoint();
 }

 std::string
 Process::absolutePath(const std::string &filename, bool host_filesystem)
 {
     if (filename.empty() || startswith(filename, "/"))
         return filename;

     // Construct the absolute path given the current working directory for
     // either the host filesystem or target filesystem. The distinction only
     // matters if filesystem redirection is utilized in the simulation.
     auto path_base = std::string();
     if (host_filesystem) {
         path_base = hostCwd;
         assert(!hostCwd.empty());
     } else {
         path_base = tgtCwd;
         assert(!tgtCwd.empty());
     }

     // Add a trailing '/' if the current working directory did not have one.
     normalize(path_base);

     // Append the filename onto the current working path.
     auto absolute_path = path_base + filename;

     return absolute_path;
 }

 Process *
 ProcessParams::create() const
 {
     // If not specified, set the executable parameter equal to the
     // simulated system's zeroth command line parameter
     const std::string &exec = (executable == "") ? cmd[0] : executable;

     auto *obj_file = loader::createObjectFile(exec);
     fatal_if(!obj_file, "Cannot load object file %s.", exec);

     Process *process = Process::tryLoaders(*this, obj_file);
     fatal_if(!process, "Unknown error creating process object.");

     return process;
 }

 } // namespace gem5
	/*
	* Copyright (c) 2014-2016 Advanced Micro Devices, Inc.
	* Copyright (c) 2012 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.
	*
	* Copyright (c) 2001-2005 The Regents of The University of Michigan
	* All rights reserved.
	*
	* 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.
	*/

	#include "sim/process.hh"

	#include <fcntl.h>
	#include <unistd.h>

	#include <array>
	#include <climits>
	#include <csignal>
	#include <map>
	#include <string>
	#include <vector>

	#include "base/intmath.hh"
	#include "base/loader/object_file.hh"
	#include "base/loader/symtab.hh"
	#include "base/statistics.hh"
	#include "cpu/thread_context.hh"
	#include "mem/page_table.hh"
	#include "mem/se_translating_port_proxy.hh"
	#include "params/Process.hh"
	#include "sim/emul_driver.hh"
	#include "sim/fd_array.hh"
	#include "sim/fd_entry.hh"
	#include "sim/redirect_path.hh"
	#include "sim/se_workload.hh"
	#include "sim/syscall_desc.hh"
	#include "sim/system.hh"

	namespace gem5
	{

	namespace
	{

	typedef std::vector<Process::Loader *> LoaderList;

	LoaderList &
	process_loaders()
	{
	static LoaderList loaders;
	return loaders;
	}

	} // anonymous namespace

	Process::Loader::Loader()
	{
	process_loaders().emplace_back(this);
	}

	Process *
	Process::tryLoaders(const ProcessParams &params,
	loader::ObjectFile *obj_file)
	{
	for (auto &loader_it : process_loaders()) {
	Process *p = loader_it->load(params, obj_file);
	if (p)
	return p;
	}

	return nullptr;
	}

	static std::string
	normalize(const std::string& directory)
	{
	if (directory.back() != '/')
	return directory + '/';
	return directory;
	}

	Process::Process(const ProcessParams &params, EmulationPageTable *pTable,
	loader::ObjectFile *obj_file)
	: SimObject(params), system(params.system),
	seWorkload(dynamic_cast<SEWorkload *>(system->workload)),
	useArchPT(params.useArchPT),
	kvmInSE(params.kvmInSE),
	useForClone(false),
	pTable(pTable),
	objFile(obj_file),
	argv(params.cmd), envp(params.env),
	executable(params.executable == "" ? params.cmd[0] : params.executable),
	tgtCwd(normalize(params.cwd)),
	hostCwd(checkPathRedirect(tgtCwd)),
	release(params.release),
	_uid(params.uid), _euid(params.euid),
	_gid(params.gid), _egid(params.egid),
	_pid(params.pid), _ppid(params.ppid),
	_pgid(params.pgid), drivers(params.drivers),
	fds(std::make_shared<FDArray>(
	params.input, params.output, params.errout)),
	childClearTID(0),
	ADD_STAT(numSyscalls, statistics::units::Count::get(),
	"Number of system calls")
	{
	fatal_if(!seWorkload, "Couldn't find appropriate workload object.");
	fatal_if(_pid >= System::maxPID, "_pid is too large: %d", _pid);

	auto ret_pair = system->PIDs.emplace(_pid);
	fatal_if(!ret_pair.second, "_pid %d is already used", _pid);

	/**
	* Linux bundles together processes into this concept called a thread
	* group. The thread group is responsible for recording which processes
	* behave as threads within a process context. The thread group leader
	* is the process who's tgid is equal to its pid. Other processes which
	* belong to the thread group, but do not lead the thread group, are
	* treated as child threads. These threads are created by the clone system
	* call with options specified to create threads (differing from the
	* options used to implement a fork). By default, set up the tgid/pid
	* with a new, equivalent value. If CLONE_THREAD is specified, patch
	* the tgid value with the old process' value.
	*/
	_tgid = params.pid;

	exitGroup = new bool();
	sigchld = new bool();

	image = objFile->buildImage();

	if (loader::debugSymbolTable.empty())
	loader::debugSymbolTable = objFile->symtab();
	}

	void
	Process::clone(ThreadContext otc, ThreadContext ntc,
	Process *np, RegVal flags)
	{
	#ifndef CLONE_VM
	#define CLONE_VM 0
	#endif
	#ifndef CLONE_FILES
	#define CLONE_FILES 0
	#endif
	#ifndef CLONE_THREAD
	#define CLONE_THREAD 0
	#endif
	#ifndef CLONE_VFORK
	#define CLONE_VFORK 0
	#endif
	if (CLONE_VM & flags) {
	/**
	* Share the process memory address space between the new process
	* and the old process. Changes in one will be visible in the other
	* due to the pointer use.
	*/
	delete np->pTable;
	np->pTable = pTable;

	np->memState = memState;
	} else {
	/**
	* Duplicate the process memory address space. The state needs to be
	* copied over (rather than using pointers to share everything).
	*/
	typedef std::vector<std::pair<Addr,Addr>> MapVec;
	MapVec mappings;
	pTable->getMappings(&mappings);

	for (auto map : mappings) {
	Addr paddr, vaddr = map.first;
	bool alloc_page = !(np->pTable->translate(vaddr, paddr));
	np->replicatePage(vaddr, paddr, otc, ntc, alloc_page);
	}

	np->memState = memState;
	}

	if (CLONE_FILES & flags) {
	/**
	* The parent and child file descriptors are shared because the
	* two FDArray pointers are pointing to the same FDArray. Opening
	* and closing file descriptors will be visible to both processes.
	*/
	np->fds = fds;
	} else {
	/**
	* Copy the file descriptors from the old process into the new
	* child process. The file descriptors entry can be opened and
	* closed independently of the other process being considered. The
	* host file descriptors are also dup'd so that the flags for the
	* host file descriptor is independent of the other process.
	*/
	std::shared_ptr<FDArray> nfds = np->fds;
	for (int tgt_fd = 0; tgt_fd < fds->getSize(); tgt_fd++) {
	std::shared_ptr<FDEntry> this_fde = (*fds)[tgt_fd];
	if (!this_fde) {
	nfds->setFDEntry(tgt_fd, nullptr);
	continue;
	}
	nfds->setFDEntry(tgt_fd, this_fde->clone());

	auto this_hbfd = std::dynamic_pointer_cast<HBFDEntry>(this_fde);
	if (!this_hbfd)
	continue;

	int this_sim_fd = this_hbfd->getSimFD();
	if (this_sim_fd <= 2)
	continue;

	int np_sim_fd = dup(this_sim_fd);
	assert(np_sim_fd != -1);

	auto nhbfd = std::dynamic_pointer_cast<HBFDEntry>((*nfds)[tgt_fd]);
	nhbfd->setSimFD(np_sim_fd);
	}
	}

	if (CLONE_THREAD & flags) {
	np->_tgid = _tgid;
	delete np->exitGroup;
	np->exitGroup = exitGroup;
	}

	if (CLONE_VFORK & flags) {
	np->vforkContexts.push_back(otc->contextId());
	}

	np->argv.insert(np->argv.end(), argv.begin(), argv.end());
	np->envp.insert(np->envp.end(), envp.begin(), envp.end());
	}

	void
	Process::revokeThreadContext(int context_id)
	{
	std::vector<ContextID>::iterator it;
	for (it = contextIds.begin(); it != contextIds.end(); it++) {
	if (*it == context_id) {
	contextIds.erase(it);
	return;
	}
	}
	warn("Unable to find thread context to revoke");
	}

	void
	Process::init()
	{
	// Patch the ld_bias for dynamic executables.
	updateBias();

	if (objFile->getInterpreter())
	interpImage = objFile->getInterpreter()->buildImage();
	}

	void
	Process::initState()
	{
	if (contextIds.empty())
	fatal("Process %s is not associated with any HW contexts!\n", name());

	// first thread context for this process... initialize & enable
	ThreadContext *tc = system->threads[contextIds[0]];

	// mark this context as active so it will start ticking.
	tc->activate();

	pTable->initState();

	initVirtMem.reset(new SETranslatingPortProxy(
	tc, SETranslatingPortProxy::Always));

	// load object file into target memory
	image.write(*initVirtMem);
	interpImage.write(*initVirtMem);
	}

	DrainState
	Process::drain()
	{
	fds->updateFileOffsets();
	return DrainState::Drained;
	}

	void
	Process::allocateMem(Addr vaddr, int64_t size, bool clobber)
	{
	const auto page_size = pTable->pageSize();

	const Addr page_addr = roundDown(vaddr, page_size);

	// Check if the page has been mapped by other cores if not to clobber.
	// When running multithreaded programs in SE-mode with DerivO3CPU model,
	// there are cases where two or more cores have page faults on the same
	// page in nearby ticks. When the cores try to handle the faults at the
	// commit stage (also in nearby ticks/cycles), the first core will ask for
	// a physical page frame to map with the virtual page. Other cores can
	// return if the page has been mapped and `!clobber`.
	if (!clobber) {
	const EmulationPageTable::Entry *pte = pTable->lookup(page_addr);
	if (pte) {
	warn("Process::allocateMem: addr %#x already mapped\n", vaddr);
	return;
	}
	}

	const int npages = divCeil(size, page_size);
	const Addr paddr = seWorkload->allocPhysPages(npages);
	const Addr pages_size = npages * page_size;
	pTable->map(page_addr, paddr, pages_size,
	clobber ? EmulationPageTable::Clobber :
	EmulationPageTable::MappingFlags(0));
	}

	void
	Process::replicatePage(Addr vaddr, Addr new_paddr, ThreadContext *old_tc,
	ThreadContext *new_tc, bool allocate_page)
	{
	if (allocate_page)
	new_paddr = seWorkload->allocPhysPages(1);

	// Read from old physical page.
	uint8_t buf_p[pTable->pageSize()];
	SETranslatingPortProxy(old_tc).readBlob(vaddr, buf_p, sizeof(buf_p));

	// Create new mapping in process address space by clobbering existing
	// mapping (if any existed) and then write to the new physical page.
	bool clobber = true;
	pTable->map(vaddr, new_paddr, sizeof(buf_p), clobber);
	SETranslatingPortProxy(new_tc).writeBlob(vaddr, buf_p, sizeof(buf_p));
	}

	bool
	Process::fixupFault(Addr vaddr)
	{
	return memState->fixupFault(vaddr);
	}

	void
	Process::serialize(CheckpointOut &cp) const
	{
	memState->serialize(cp);
	pTable->serialize(cp);
	fds->serialize(cp);

	/**
	* Checkpoints for pipes, device drivers or sockets currently
	* do not work. Need to come back and fix them at a later date.
	*/

	warn("Checkpoints for pipes, device drivers and sockets do not work.");
	}

	void
	Process::unserialize(CheckpointIn &cp)
	{
	memState->unserialize(cp);
	pTable->unserialize(cp);
	fds->unserialize(cp);

	/**
	* Checkpoints for pipes, device drivers or sockets currently
	* do not work. Need to come back and fix them at a later date.
	*/
	warn("Checkpoints for pipes, device drivers and sockets do not work.");
	// The above returns a bool so that you could do something if you don't
	// find the param in the checkpoint if you wanted to, like set a default
	// but in this case we'll just stick with the instantiated value if not
	// found.
	}

	bool
	Process::map(Addr vaddr, Addr paddr, int size, bool cacheable)
	{
	pTable->map(vaddr, paddr, size,
	cacheable ? EmulationPageTable::MappingFlags(0) :
	EmulationPageTable::Uncacheable);
	return true;
	}

	EmulatedDriver *
	Process::findDriver(std::string filename)
	{
	for (EmulatedDriver *d : drivers) {
	if (d->match(filename))
	return d;
	}

	return nullptr;
	}

	std::string
	Process::checkPathRedirect(const std::string &filename)
	{
	// If the input parameter contains a relative path, convert it.
	// The target version of the current working directory is fine since
	// we immediately convert it using redirect paths into a host version.
	auto abs_path = absolutePath(filename, false);

	for (auto path : system->redirectPaths) {
	// Search through the redirect paths to see if a starting substring of
	// our path falls into any buckets which need to redirected.
	if (startswith(abs_path, path->appPath())) {
	std::string tail = abs_path.substr(path->appPath().size());

	// If this path needs to be redirected, search through a list
	// of targets to see if we can match a valid file (or directory).
	for (auto host_path : path->hostPaths()) {
	if (access((host_path + tail).c_str(), R_OK) == 0) {
	// Return the valid match.
	return host_path + tail;
	}
	}
	// The path needs to be redirected, but the file or directory
	// does not exist on the host filesystem. Return the first
	// host path as a default.
	return path->hostPaths()[0] + tail;
	}
	}

	// The path does not need to be redirected.
	return abs_path;
	}

	void
	Process::updateBias()
	{
	auto *interp = objFile->getInterpreter();

	if (!interp \|\| !interp->relocatable())
	return;

	// Determine how large the interpreters footprint will be in the process
	// address space.
	Addr interp_mapsize = roundUp(interp->mapSize(), pTable->pageSize());

	// We are allocating the memory area; set the bias to the lowest address
	// in the allocated memory region.
	Addr mmap_end = memState->getMmapEnd();
	Addr ld_bias = mmapGrowsDown() ? mmap_end - interp_mapsize : mmap_end;

	// Adjust the process mmap area to give the interpreter room; the real
	// execve system call would just invoke the kernel's internal mmap
	// functions to make these adjustments.
	mmap_end = mmapGrowsDown() ? ld_bias : mmap_end + interp_mapsize;
	memState->setMmapEnd(mmap_end);

	interp->updateBias(ld_bias);
	}

	loader::ObjectFile *
	Process::getInterpreter()
	{
	return objFile->getInterpreter();
	}

	Addr
	Process::getBias()
	{
	auto *interp = getInterpreter();

	return interp ? interp->bias() : objFile->bias();
	}

	Addr
	Process::getStartPC()
	{
	auto *interp = getInterpreter();

	return interp ? interp->entryPoint() : objFile->entryPoint();
	}

	std::string
	Process::absolutePath(const std::string &filename, bool host_filesystem)
	{
	if (filename.empty() \|\| startswith(filename, "/"))
	return filename;

	// Construct the absolute path given the current working directory for
	// either the host filesystem or target filesystem. The distinction only
	// matters if filesystem redirection is utilized in the simulation.
	auto path_base = std::string();
	if (host_filesystem) {
	path_base = hostCwd;
	assert(!hostCwd.empty());
	} else {
	path_base = tgtCwd;
	assert(!tgtCwd.empty());
	}

	// Add a trailing '/' if the current working directory did not have one.
	normalize(path_base);

	// Append the filename onto the current working path.
	auto absolute_path = path_base + filename;

	return absolute_path;
	}

	Process *
	ProcessParams::create() const
	{
	// If not specified, set the executable parameter equal to the
	// simulated system's zeroth command line parameter
	const std::string &exec = (executable == "") ? cmd[0] : executable;

	auto *obj_file = loader::createObjectFile(exec);
	fatal_if(!obj_file, "Cannot load object file %s.", exec);

	Process process = Process::tryLoaders(this, obj_file);
	fatal_if(!process, "Unknown error creating process object.");

	return process;
	}

	} // namespace gem5