[Hotfix] Mark python-FFI handling with TVM_DLL (apache#15970)

* [Hotfix] Mark python-FFI handling with TVM_DLL

Bugfix for builds on Windows.

* Updated declarations to match other usage in c_runtime_api.h

include/tvm/runtime/c_runtime_api.h

@@ -251,6 +251,18 @@ TVM_DLL void TVMAPISetLastError(const char* msg);
  */
 TVM_DLL void TVMAPISetLastPythonError(void* py_object);
 
+/*! \brief Return the previous python error, if any.
+ *
+ * Used to propagate the original Python exception to a python
+ * try/except, when there are C++ stack frames between the location thro
+ *
+ * \return The previous argument passed during the most recent call to
+ *     TVMAPISetLastPythonError.  If TVMAPISetLastPythonError has not
+ *     been called, or if TVMDropLastPythonError has been called since
+ *     the most recent to TVMAPISetLastPythonError, returns nullptr.
+ */
+TVM_DLL void* TVMGetLastPythonError();
+
 /*!
  * \brief return str message of the last error
  *  all function in this file will return 0 when success
@@ -261,6 +273,42 @@ TVM_DLL void TVMAPISetLastPythonError(void* py_object);
  *  \return error info
  */
 TVM_DLL const char* TVMGetLastError(void);
+
+/*!
+ * \brief Return the backtrace of the most recent error
+ *
+ * Returns the backtrace of the most recent error, if an error exists,
+ * and the error contains a backtrace.  If no error exists or the
+ * error does not contain a backtrace, returns nullptr.
+ *
+ *  \return The backtrace of the most recent error
+ */
+TVM_DLL const char* TVMGetLastBacktrace();
+
+/*!
+ * \brief Remove the propagated python error, if any
+ *
+ * Removes the TVM-held reference to a thrown python exception object.
+ * Because these objects contain references to the stack frames from
+ * which the exception was thrown, maintaining a reference to an
+ * exception object prevents any local python variables from being
+ * garbage-collected.  After retrieving the object using
+ * TVMGetLastPythonError, the Python FFI interface uses this method to
+ * clear the TVM-held reference to the exception, to allow garbage
+ * collection to continue.
+ */
+TVM_DLL void TVMDropLastPythonError();
+
+/*! \brief Re-throw the most recent error.
+ *
+ * If an error was previously set using TVMAPISetLastError or
+ * TVMAPISetLastPythonError, re-throw the error.  This is similar to
+ * `LOG(FATAL) << TVMGetLastError()`, but includes handling to
+ * propagate a python exception across C++ stack frames, or to append
+ * a stack trace to an error message.
+ */
+TVM_DLL void TVMThrowLastError();
+
 /*!
  * \brief Load module from file.
  * \param file_name The file name to load the module from.

src/runtime/c_runtime_api.cc

@@ -418,7 +418,7 @@ const char* TVMGetLastError() {
   }
 }
 
-extern "C" void* TVMGetLastPythonError() {
+void* TVMGetLastPythonError() {
   auto& last_error = TVMAPIRuntimeStore::Get()->last_error;
   if (auto* wrapped = std::get_if<WrappedPythonError>(&last_error)) {
     return wrapped->obj.raw_pointer();
@@ -427,7 +427,7 @@ extern "C" void* TVMGetLastPythonError() {
   }
 }
 
-extern "C" const char* TVMGetLastBacktrace() {
+const char* TVMGetLastBacktrace() {
   const auto& last_error = TVMAPIRuntimeStore::Get()->last_error;
   if (const auto* wrapped = std::get_if<WrappedPythonError>(&last_error)) {
     return wrapped->cpp_backtrace.data();
@@ -438,7 +438,7 @@ extern "C" const char* TVMGetLastBacktrace() {
   }
 }
 
-extern "C" void TVMDropLastPythonError() {
+void TVMDropLastPythonError() {
   auto& last_error = TVMAPIRuntimeStore::Get()->last_error;
   if (std::get_if<WrappedPythonError>(&last_error)) {
     last_error = "";
@@ -458,12 +458,12 @@ int TVMAPIHandleException(const std::exception& e) {
   return -1;
 }
 
-extern "C" void TVMAPISetLastPythonError(void* obj) {
+void TVMAPISetLastPythonError(void* obj) {
   auto& last_error = TVMAPIRuntimeStore::Get()->last_error;
   last_error = WrappedPythonError(WrappedPythonObject(obj));
 }
 
-void ThrowLastError() {
+void TVMThrowLastError() {
   auto& last_error = TVMAPIRuntimeStore::Get()->last_error;
   if (auto* wrapped = std::get_if<WrappedPythonError>(&last_error)) {
     WrappedPythonError wrapped_err;
@@ -611,7 +611,7 @@ int TVMFuncCreateFromCFunc(TVMPackedCFunc func, void* resource_handle, TVMPacked
       int ret = func(const_cast<TVMValue*>(args.values), const_cast<int*>(args.type_codes),
                      args.num_args, rv, resource_handle);
       if (ret != 0) {
-        ThrowLastError();
+        TVMThrowLastError();
       }
     });
     TVMValue val;
@@ -627,7 +627,7 @@ int TVMFuncCreateFromCFunc(TVMPackedCFunc func, void* resource_handle, TVMPacked
       int ret = func(const_cast<TVMValue*>(args.values), const_cast<int*>(args.type_codes),
                      args.num_args, rv, rpack.get());
       if (ret != 0) {
-        ThrowLastError();
+        TVMThrowLastError();
       }
     });
     TVMValue val;