Merge pull request #530 from undingen/register_statics

When loading a shared library let the GC know about the static variables

src/gc/collector.cpp

@@ -142,6 +142,11 @@ void deregisterPermanentRoot(void* obj) {
     roots.erase(obj);
 }
 
+static std::vector<std::pair<void*, void*>> potential_root_ranges;
+void registerPotentialRootRange(void* start, void* end) {
+    potential_root_ranges.push_back(std::make_pair(start, end));
+}
+
 extern "C" PyObject* PyGC_AddRoot(PyObject* obj) noexcept {
     if (obj) {
         // Allow duplicates from CAPI code since they shouldn't have to know
@@ -268,6 +273,10 @@ void markPhase() {
         visitor.visit(h->value);
     }
 
+    for (auto& e : potential_root_ranges) {
+        visitor.visitPotentialRange((void* const*)e.first, (void* const*)e.second);
+    }
+
     // if (VERBOSITY()) printf("Found %d roots\n", stack.size());
     while (void* p = stack.pop()) {
         assert(((intptr_t)p) % 8 == 0);

src/gc/collector.h

@@ -33,6 +33,8 @@ void deregisterPermanentRoot(void* root_obj);
 // even if they are not heap allocated.
 void registerNonheapRootObject(void* obj);
 
+void registerPotentialRootRange(void* start, void* end);
+
 // If you want to have a static root "location" where multiple values could be stored, use this:
 class GCRootHandle {
 public:

src/runtime/capi.cpp

@@ -1309,6 +1309,15 @@ BoxedModule* importCExtension(const std::string& full_name, const std::string& l
 
     assert(init);
 
+    // Let the GC know about the static variables.
+    uintptr_t bss_start = (uintptr_t)dlsym(handle, "__bss_start");
+    uintptr_t bss_end = (uintptr_t)dlsym(handle, "_end");
+    RELEASE_ASSERT(bss_end - bss_start < 100000, "Large BSS section detected - there maybe something wrong");
+    // only track void* aligned memory
+    bss_start = (bss_start + (sizeof(void*) - 1)) & ~(sizeof(void*) - 1);
+    bss_end -= bss_end % sizeof(void*);
+    gc::registerPotentialRootRange((void*)bss_start, (void*)bss_end);
+
     char* packagecontext = strdup(full_name.c_str());
     char* oldcontext = _Py_PackageContext;
     _Py_PackageContext = packagecontext;