sim: Refactor the serialization base class

Objects that are can be serialized are supposed to inherit from the
Serializable class. This class is meant to provide a unified API for
such objects. However, so far it has mainly been used by SimObjects
due to some fundamental design limitations. This changeset redesigns
to the serialization interface to make it more generic and hide the
underlying checkpoint storage. Specifically:

  * Add a set of APIs to serialize into a subsection of the current
    object. Previously, objects that needed this functionality would
    use ad-hoc solutions using nameOut() and section name
    generation. In the new world, an object that implements the
    interface has the methods serializeSection() and
    unserializeSection() that serialize into a named /subsection/ of
    the current object. Calling serialize() serializes an object into
    the current section.

  * Move the name() method from Serializable to SimObject as it is no
    longer needed for serialization. The fully qualified section name
    is generated by the main serialization code on the fly as objects
    serialize sub-objects.

  * Add a scoped ScopedCheckpointSection helper class. Some objects
    need to serialize data structures, that are not deriving from
    Serializable, into subsections. Previously, this was done using
    nameOut() and manual section name generation. To simplify this,
    this changeset introduces a ScopedCheckpointSection() helper
    class. When this class is instantiated, it adds a new /subsection/
    and subsequent serialization calls during the lifetime of this
    helper class happen inside this section (or a subsection in case
    of nested sections).

  * The serialize() call is now const which prevents accidental state
    manipulation during serialization. Objects that rely on modifying
    state can use the serializeOld() call instead. The default
    implementation simply calls serialize(). Note: The old-style calls
    need to be explicitly called using the
    serializeOld()/serializeSectionOld() style APIs. These are used by
    default when serializing SimObjects.

  * Both the input and output checkpoints now use their own named
    types. This hides underlying checkpoint implementation from
    objects that need checkpointing and makes it easier to change the
    underlying checkpoint storage code.

10 files changed, 56 insertions, 67 deletions

diff --git a/src/mem/cache/cache.hh b/src/mem/cache/cache.hh
index 4c70d3a40..27d4b9ee1 100644
--- a/src/mem/cache/cache.hh
+++ b/src/mem/cache/cache.hh
@@ -429,8 +429,8 @@ class Cache : public BaseCache
     /** serialize the state of the caches
      * We currently don't support checkpointing cache state, so this panics.
      */
-    virtual void serialize(std::ostream &os);
-    void unserialize(Checkpoint *cp, const std::string &section);
+    void serialize(CheckpointOut &cp) const M5_ATTR_OVERRIDE;
+    void unserialize(CheckpointIn &cp) M5_ATTR_OVERRIDE;
 };
 
 /**
diff --git a/src/mem/cache/cache_impl.hh b/src/mem/cache/cache_impl.hh
index 94a3ad4ee..03593554a 100644
--- a/src/mem/cache/cache_impl.hh
+++ b/src/mem/cache/cache_impl.hh
@@ -2292,7 +2292,7 @@ Cache::nextMSHRReadyTime() const
 }
 
 void
-Cache::serialize(std::ostream &os)
+Cache::serialize(CheckpointOut &cp) const
 {
     bool dirty(isDirty());
 
@@ -2312,7 +2312,7 @@ Cache::serialize(std::ostream &os)
 }
 
 void
-Cache::unserialize(Checkpoint *cp, const std::string &section)
+Cache::unserialize(CheckpointIn &cp)
 {
     bool bad_checkpoint;
     UNSERIALIZE_SCALAR(bad_checkpoint);
diff --git a/src/mem/multi_level_page_table.hh b/src/mem/multi_level_page_table.hh
index 232121c21..f622bbbed 100644
--- a/src/mem/multi_level_page_table.hh
+++ b/src/mem/multi_level_page_table.hh
@@ -153,7 +153,7 @@ public:
     void unmap(Addr vaddr, int64_t size);
     bool isUnmapped(Addr vaddr, int64_t size);
     bool lookup(Addr vaddr, TheISA::TlbEntry &entry);
-    void serialize(std::ostream &os);
-    void unserialize(Checkpoint *cp, const std::string &section);
+    void serialize(CheckpointOut &cp) const M5_ATTR_OVERRIDE;
+    void unserialize(CheckpointIn &cp) M5_ATTR_OVERRIDE;
 };
 #endif // __MEM_MULTI_LEVEL_PAGE_TABLE_HH__
diff --git a/src/mem/multi_level_page_table_impl.hh b/src/mem/multi_level_page_table_impl.hh
index 6714a170e..610240562 100644
--- a/src/mem/multi_level_page_table_impl.hh
+++ b/src/mem/multi_level_page_table_impl.hh
@@ -314,19 +314,18 @@ MultiLevelPageTable<ISAOps>::lookup(Addr vaddr, TlbEntry &entry)
 
 template <class ISAOps>
 void
-MultiLevelPageTable<ISAOps>::serialize(std::ostream &os)
+MultiLevelPageTable<ISAOps>::serialize(CheckpointOut &cp) const
 {
     /** Since, the page table is stored in system memory
      * which is serialized separately, we will serialize
      * just the base pointer
      */
-    paramOut(os, "ptable.pointer", basePtr);
+    paramOut(cp, "ptable.pointer", basePtr);
 }
 
 template <class ISAOps>
 void
-MultiLevelPageTable<ISAOps>::unserialize(Checkpoint *cp,
-                                         const std::string &section)
+MultiLevelPageTable<ISAOps>::unserialize(CheckpointIn &cp)
 {
-    paramIn(cp, section, "ptable.pointer", basePtr);
+    paramIn(cp, "ptable.pointer", basePtr);
 }
diff --git a/src/mem/page_table.cc b/src/mem/page_table.cc
index d3af09e1e..6875d6f9b 100644
--- a/src/mem/page_table.cc
+++ b/src/mem/page_table.cc
@@ -37,6 +37,7 @@
  */
 #include <fstream>
 #include <map>
+#include <memory>
 #include <string>
 
 #include "base/bitfield.hh"
@@ -196,44 +197,37 @@ PageTableBase::translate(RequestPtr req)
 }
 
 void
-FuncPageTable::serialize(std::ostream &os)
+FuncPageTable::serialize(CheckpointOut &cp) const
 {
-    paramOut(os, "ptable.size", pTable.size());
+    paramOut(cp, "ptable.size", pTable.size());
 
     PTable::size_type count = 0;
+    for (auto &pte : pTable) {
+        ScopedCheckpointSection sec(cp, csprintf("Entry%d", count++));
 
-    PTableItr iter = pTable.begin();
-    PTableItr end = pTable.end();
-    while (iter != end) {
-        os << "\n[" << csprintf("%s.Entry%d", name(), count) << "]\n";
-
-        paramOut(os, "vaddr", iter->first);
-        iter->second.serialize(os);
-
-        ++iter;
-        ++count;
+        paramOut(cp, "vaddr", pte.first);
+        pte.second.serialize(cp);
     }
     assert(count == pTable.size());
 }
 
 void
-FuncPageTable::unserialize(Checkpoint *cp, const std::string &section)
+FuncPageTable::unserialize(CheckpointIn &cp)
 {
-    int i = 0, count;
-    paramIn(cp, section, "ptable.size", count);
+    int count;
+    paramIn(cp, "ptable.size", count);
 
-    pTable.clear();
+    for (int i = 0; i < count; ++i) {
+        ScopedCheckpointSection sec(cp, csprintf("Entry%d", i));
 
-    while (i < count) {
-        TheISA::TlbEntry *entry;
+        std::unique_ptr<TheISA::TlbEntry> entry;
         Addr vaddr;
 
-        paramIn(cp, csprintf("%s.Entry%d", name(), i), "vaddr", vaddr);
-        entry = new TheISA::TlbEntry();
-        entry->unserialize(cp, csprintf("%s.Entry%d", name(), i));
+        paramIn(cp, "vaddr", vaddr);
+        entry.reset(new TheISA::TlbEntry());
+        entry->unserialize(cp);
+
         pTable[vaddr] = *entry;
-        delete entry;
-        ++i;
     }
 }
 
diff --git a/src/mem/page_table.hh b/src/mem/page_table.hh
index 22b5c61eb..ddec104a7 100644
--- a/src/mem/page_table.hh
+++ b/src/mem/page_table.hh
@@ -53,7 +53,7 @@ class ThreadContext;
 /**
  * Declaration of base class for page table
  */
-class PageTableBase
+class PageTableBase : public Serializable
 {
   protected:
     struct cacheElement {
@@ -192,10 +192,6 @@ class PageTableBase
             pTableCache[2].valid = false;
         }
     }
-
-    virtual void serialize(std::ostream &os) = 0;
-
-    virtual void unserialize(Checkpoint *cp, const std::string &section) = 0;
 };
 
 /**
@@ -239,9 +235,8 @@ class FuncPageTable : public PageTableBase
      */
     bool lookup(Addr vaddr, TheISA::TlbEntry &entry);
 
-    void serialize(std::ostream &os);
-
-    void unserialize(Checkpoint *cp, const std::string &section);
+    void serialize(CheckpointOut &cp) const M5_ATTR_OVERRIDE;
+    void unserialize(CheckpointIn &cp) M5_ATTR_OVERRIDE;
 };
 
 /**
diff --git a/src/mem/physical.cc b/src/mem/physical.cc
index e6d682624..d757b8c5d 100644
--- a/src/mem/physical.cc
+++ b/src/mem/physical.cc
@@ -289,7 +289,7 @@ PhysicalMemory::functionalAccess(PacketPtr pkt)
 }
 
 void
-PhysicalMemory::serialize(ostream& os)
+PhysicalMemory::serialize(CheckpointOut &cp) const
 {
     // serialize all the locked addresses and their context ids
     vector<Addr> lal_addr;
@@ -303,8 +303,8 @@ PhysicalMemory::serialize(ostream& os)
         }
     }
 
-    arrayParamOut(os, "lal_addr", lal_addr);
-    arrayParamOut(os, "lal_cid", lal_cid);
+    SERIALIZE_CONTAINER(lal_addr);
+    SERIALIZE_CONTAINER(lal_cid);
 
     // serialize the backing stores
     unsigned int nbr_of_stores = backingStore.size();
@@ -313,14 +313,14 @@ PhysicalMemory::serialize(ostream& os)
     unsigned int store_id = 0;
     // store each backing store memory segment in a file
     for (auto& s : backingStore) {
-        nameOut(os, csprintf("%s.store%d", name(), store_id));
-        serializeStore(os, store_id++, s.first, s.second);
+        ScopedCheckpointSection sec(cp, csprintf("store%d", store_id));
+        serializeStore(cp, store_id++, s.first, s.second);
     }
 }
 
 void
-PhysicalMemory::serializeStore(ostream& os, unsigned int store_id,
-                               AddrRange range, uint8_t* pmem)
+PhysicalMemory::serializeStore(CheckpointOut &cp, unsigned int store_id,
+                               AddrRange range, uint8_t* pmem) const
 {
     // we cannot use the address range for the name as the
     // memories that are not part of the address map can overlap
@@ -335,7 +335,7 @@ PhysicalMemory::serializeStore(ostream& os, unsigned int store_id,
     SERIALIZE_SCALAR(range_size);
 
     // write memory file
-    string filepath = Checkpoint::dir() + "/" + filename.c_str();
+    string filepath = CheckpointIn::dir() + "/" + filename.c_str();
     gzFile compressed_mem = gzopen(filepath.c_str(), "wb");
     if (compressed_mem == NULL)
         fatal("Can't open physical memory checkpoint file '%s'\n",
@@ -365,14 +365,14 @@ PhysicalMemory::serializeStore(ostream& os, unsigned int store_id,
 }
 
 void
-PhysicalMemory::unserialize(Checkpoint* cp, const string& section)
+PhysicalMemory::unserialize(CheckpointIn &cp)
 {
     // unserialize the locked addresses and map them to the
     // appropriate memory controller
     vector<Addr> lal_addr;
     vector<int> lal_cid;
-    arrayParamIn(cp, section, "lal_addr", lal_addr);
-    arrayParamIn(cp, section, "lal_cid", lal_cid);
+    UNSERIALIZE_CONTAINER(lal_addr);
+    UNSERIALIZE_CONTAINER(lal_cid);
     for(size_t i = 0; i < lal_addr.size(); ++i) {
         const auto& m = addrMap.find(lal_addr[i]);
         m->second->addLockedAddr(LockedAddr(lal_addr[i], lal_cid[i]));
@@ -383,13 +383,14 @@ PhysicalMemory::unserialize(Checkpoint* cp, const string& section)
     UNSERIALIZE_SCALAR(nbr_of_stores);
 
     for (unsigned int i = 0; i < nbr_of_stores; ++i) {
-        unserializeStore(cp, csprintf("%s.store%d", section, i));
+        ScopedCheckpointSection sec(cp, csprintf("store%d", i));
+        unserializeStore(cp);
     }
 
 }
 
 void
-PhysicalMemory::unserializeStore(Checkpoint* cp, const string& section)
+PhysicalMemory::unserializeStore(CheckpointIn &cp)
 {
     const uint32_t chunk_size = 16384;
 
@@ -398,7 +399,7 @@ PhysicalMemory::unserializeStore(Checkpoint* cp, const string& section)
 
     string filename;
     UNSERIALIZE_SCALAR(filename);
-    string filepath = cp->cptDir + "/" + filename;
+    string filepath = cp.cptDir + "/" + filename;
 
     // mmap memoryfile
     gzFile compressed_mem = gzopen(filepath.c_str(), "rb");
diff --git a/src/mem/physical.hh b/src/mem/physical.hh
index 0f53b1d9d..c577cd3ea 100644
--- a/src/mem/physical.hh
+++ b/src/mem/physical.hh
@@ -197,7 +197,7 @@ class PhysicalMemory : public Serializable
      *
      * @param os stream to serialize to
      */
-    void serialize(std::ostream& os);
+    void serialize(CheckpointOut &cp) const M5_ATTR_OVERRIDE;
 
     /**
      * Serialize a specific store.
@@ -206,20 +206,20 @@ class PhysicalMemory : public Serializable
      * @param range The address range of this backing store
      * @param pmem The host pointer to this backing store
      */
-    void serializeStore(std::ostream& os, unsigned int store_id,
-                        AddrRange range, uint8_t* pmem);
+    void serializeStore(CheckpointOut &cp, unsigned int store_id,
+                        AddrRange range, uint8_t* pmem) const;
 
     /**
      * Unserialize the memories in the system. As with the
      * serialization, this action is independent of how the address
      * ranges are mapped to logical memories in the guest system.
      */
-    void unserialize(Checkpoint* cp, const std::string& section);
+    void unserialize(CheckpointIn &cp) M5_ATTR_OVERRIDE;
 
     /**
      * Unserialize a specific backing store, identified by a section.
      */
-    void unserializeStore(Checkpoint* cp, const std::string& section);
+    void unserializeStore(CheckpointIn &cp);
 
 };
 
diff --git a/src/mem/ruby/system/System.cc b/src/mem/ruby/system/System.cc
index 75ebc8caf..9d63643cc 100644
--- a/src/mem/ruby/system/System.cc
+++ b/src/mem/ruby/system/System.cc
@@ -109,7 +109,7 @@ RubySystem::writeCompressedTrace(uint8_t *raw_data, string filename,
                                  uint64 uncompressed_trace_size)
 {
     // Create the checkpoint file for the memory
-    string thefile = Checkpoint::dir() + "/" + filename.c_str();
+    string thefile = CheckpointIn::dir() + "/" + filename.c_str();
 
     int fd = creat(thefile.c_str(), 0664);
     if (fd < 0) {
@@ -134,7 +134,7 @@ RubySystem::writeCompressedTrace(uint8_t *raw_data, string filename,
 }
 
 void
-RubySystem::serialize(std::ostream &os)
+RubySystem::serializeOld(CheckpointOut &cp)
 {
     m_cooldown_enabled = true;
     vector<Sequencer*> sequencer_map;
@@ -234,7 +234,7 @@ RubySystem::readCompressedTrace(string filename, uint8_t *&raw_data,
 }
 
 void
-RubySystem::unserialize(Checkpoint *cp, const string &section)
+RubySystem::unserialize(CheckpointIn &cp)
 {
     uint8_t *uncompressed_trace = NULL;
 
@@ -249,7 +249,7 @@ RubySystem::unserialize(Checkpoint *cp, const string &section)
 
     UNSERIALIZE_SCALAR(cache_trace_file);
     UNSERIALIZE_SCALAR(cache_trace_size);
-    cache_trace_file = cp->cptDir + "/" + cache_trace_file;
+    cache_trace_file = cp.cptDir + "/" + cache_trace_file;
 
     readCompressedTrace(cache_trace_file, uncompressed_trace,
                         cache_trace_size);
diff --git a/src/mem/ruby/system/System.hh b/src/mem/ruby/system/System.hh
index 45e8aa8b4..a59ade398 100644
--- a/src/mem/ruby/system/System.hh
+++ b/src/mem/ruby/system/System.hh
@@ -92,8 +92,8 @@ class RubySystem : public ClockedObject
     void collateStats() { m_profiler->collateStats(); }
     void resetStats();
 
-    void serialize(std::ostream &os);
-    void unserialize(Checkpoint *cp, const std::string &section);
+    void serializeOld(CheckpointOut &cp) M5_ATTR_OVERRIDE;
+    void unserialize(CheckpointIn &cp) M5_ATTR_OVERRIDE;
     void process();
     void startup();
     bool functionalRead(Packet *ptr);