Bug 1078837 part 2 - Replace IsSystemElf/reinterpret_cast dance with better API. r=nfroyd

mozglue/linker/BaseElf.h

@@ -79,6 +79,8 @@ public:
   }
 
   /* Appropriated Mappable */
+  /* /!\ we rely on this being nullptr for BaseElf instances, but not
+   * CustomElf instances. */
   mozilla::RefPtr<Mappable> mappable;
 
   /* Base address where the library is loaded */

mozglue/linker/CustomElf.cpp

@@ -348,9 +348,8 @@ CustomElf::GetSymbolPtrInDeps(const char *symbol) const
    * happen. */
   for (std::vector<RefPtr<LibHandle> >::const_iterator it = dependencies.begin();
        it < dependencies.end(); ++it) {
-    if (!(*it)->IsSystemElf()) {
-      sym = static_cast<BaseElf *>(
-        static_cast<CustomElf *>((*it).get()))->GetSymbolPtr(symbol, hash);
+    if (BaseElf *be = (*it)->AsBaseElf()) {
+      sym = be->GetSymbolPtr(symbol, hash);
     } else {
       sym = (*it)->GetSymbolPtr(symbol);
     }

mozglue/linker/CustomElf.h

@@ -54,6 +54,12 @@ public:
    */
   virtual void stats(const char *when) const;
 
+  /**
+   * Returns the instance, casted as BaseElf. (short of a better way to do
+   * this without RTTI)
+   */
+  virtual BaseElf *AsBaseElf() { return this; }
+
 private:
   /**
    * Scan dependent libraries to find the address corresponding to the

mozglue/linker/ElfLoader.cpp

@@ -452,8 +452,15 @@ void
 ElfLoader::Register(LibHandle *handle)
 {
   handles.push_back(handle);
-  if (dbg && !handle->IsSystemElf())
-    dbg.Add(static_cast<CustomElf *>(handle));
+}
+
+void
+ElfLoader::Register(CustomElf *handle)
+{
+  Register(static_cast<LibHandle *>(handle));
+  if (dbg) {
+    dbg.Add(handle);
+  }
 }
 
 void
@@ -466,8 +473,6 @@ ElfLoader::Forget(LibHandle *handle)
   if (it != handles.end()) {
     DEBUG_LOG("ElfLoader::Forget(%p [\"%s\"])", reinterpret_cast<void *>(handle),
                                                 handle->GetPath());
-    if (dbg && !handle->IsSystemElf())
-      dbg.Remove(static_cast<CustomElf *>(handle));
     handles.erase(it);
   } else {
     DEBUG_LOG("ElfLoader::Forget(%p [\"%s\"]): Handle not found",
@@ -475,6 +480,15 @@ ElfLoader::Forget(LibHandle *handle)
   }
 }
 
+void
+ElfLoader::Forget(CustomElf *handle)
+{
+  Forget(static_cast<LibHandle *>(handle));
+  if (dbg) {
+    dbg.Remove(handle);
+  }
+}
+
 void
 ElfLoader::Init()
 {
@@ -534,8 +548,8 @@ ElfLoader::~ElfLoader()
   for (LibHandleList::reverse_iterator it = handles.rbegin();
        it < handles.rend(); ++it) {
     if ((*it)->DirectRefCount()) {
-      if ((*it)->IsSystemElf()) {
-        static_cast<SystemElf *>(*it)->Forget();
+      if (SystemElf *se = (*it)->AsSystemElf()) {
+        se->Forget();
       } else {
         list.push_back(*it);
       }
@@ -550,7 +564,7 @@ ElfLoader::~ElfLoader()
     list = handles;
     for (LibHandleList::reverse_iterator it = list.rbegin();
          it < list.rend(); ++it) {
-      if ((*it)->IsSystemElf()) {
+      if ((*it)->AsSystemElf()) {
         DEBUG_LOG("ElfLoader::~ElfLoader(): Remaining handle for \"%s\" "
                   "[%d direct refs, %d refs total]", (*it)->GetPath(),
                   (*it)->DirectRefCount(), (*it)->refCount());
@@ -1203,11 +1217,12 @@ void SEGVHandler::handler(int signum, siginfo_t *info, void *context)
   if (info->si_code == SEGV_ACCERR) {
     mozilla::RefPtr<LibHandle> handle =
       ElfLoader::Singleton.GetHandleByPtr(info->si_addr);
-    if (handle && !handle->IsSystemElf()) {
-      DEBUG_LOG("Within the address space of a CustomElf");
-      CustomElf *elf = static_cast<CustomElf *>(static_cast<LibHandle *>(handle));
-      if (elf->mappable->ensure(info->si_addr))
+    BaseElf *elf;
+    if (handle && (elf = handle->AsBaseElf())) {
+      DEBUG_LOG("Within the address space of %s", handle->GetPath());
+      if (elf->mappable && elf->mappable->ensure(info->si_addr)) {
         return;
+      }
     }
   }
 

mozglue/linker/ElfLoader.h

@@ -64,8 +64,10 @@ IsSignalHandlingBroken();
 
 }
 
-/* Forward declaration because BaseElf.h includes ElfLoader.h */
+/* Forward declarations for use in LibHandle */
 class BaseElf;
+class CustomElf;
+class SystemElf;
 
 /**
  * Specialize RefCounted template for LibHandle. We may get references to
@@ -217,13 +219,15 @@ protected:
   virtual Mappable *GetMappable() const = 0;
 
   /**
-   * Returns whether the handle is a SystemElf or not. (short of a better way
-   * to do this without RTTI)
+   * Returns the instance, casted as the wanted type. Returns nullptr if
+   * that's not the actual type. (short of a better way to do this without
+   * RTTI)
    */
   friend class ElfLoader;
   friend class CustomElf;
   friend class SEGVHandler;
-  virtual bool IsSystemElf() const { return false; }
+  virtual BaseElf *AsBaseElf() { return nullptr; }
+  virtual SystemElf *AsSystemElf() { return nullptr; }
 
 private:
   MozRefCountType directRefCnt;
@@ -293,11 +297,11 @@ protected:
   virtual Mappable *GetMappable() const;
 
   /**
-   * Returns whether the handle is a SystemElf or not. (short of a better way
-   * to do this without RTTI)
+   * Returns the instance, casted as SystemElf. (short of a better way to do
+   * this without RTTI)
    */
   friend class ElfLoader;
-  virtual bool IsSystemElf() const { return true; }
+  virtual SystemElf *AsSystemElf() { return this; }
 
   /**
    * Remove the reference to the system linker handle. This avoids dlclose()
@@ -433,12 +437,14 @@ protected:
    * LibHandle subclass creators.
    */
   void Register(LibHandle *handle);
+  void Register(CustomElf *handle);
 
   /**
    * Forget about the given handle. This method is meant to be called by
    * LibHandle subclass destructors.
    */
   void Forget(LibHandle *handle);
+  void Forget(CustomElf *handle);
 
   /* Last error. Used for dlerror() */
   friend class SystemElf;