Fix subchannel call to align its call stack (similar to 15b37ac for parent call).

src/core/ext/filters/client_channel/subchannel.cc

@@ -38,6 +38,7 @@
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/channel/connected_channel.h"
 #include "src/core/lib/debug/stats.h"
+#include "src/core/lib/gpr/alloc.h"
 #include "src/core/lib/gprpp/debug_location.h"
 #include "src/core/lib/gprpp/manual_constructor.h"
 #include "src/core/lib/gprpp/ref_counted_ptr.h"
@@ -140,9 +141,13 @@ struct grpc_subchannel_call {
   grpc_closure* schedule_closure_after_destroy;
 };
 
-#define SUBCHANNEL_CALL_TO_CALL_STACK(call) ((grpc_call_stack*)((call) + 1))
-#define CALLSTACK_TO_SUBCHANNEL_CALL(callstack) \
-  (((grpc_subchannel_call*)(callstack)) - 1)
+#define SUBCHANNEL_CALL_TO_CALL_STACK(call)                          \
+  (grpc_call_stack*)((char*)(call) + GPR_ROUND_UP_TO_ALIGNMENT_SIZE( \
+                                         sizeof(grpc_subchannel_call)))
+#define CALLSTACK_TO_SUBCHANNEL_CALL(callstack)           \
+  (grpc_subchannel_call*)(((char*)(call_stack)) -         \
+                          GPR_ROUND_UP_TO_ALIGNMENT_SIZE( \
+                              sizeof(grpc_subchannel_call)))
 
 static void on_subchannel_connected(void* subchannel, grpc_error* error);
 
@@ -783,9 +788,17 @@ void ConnectedSubchannel::Ping(grpc_closure* on_initiate,
 
 grpc_error* ConnectedSubchannel::CreateCall(const CallArgs& args,
                                             grpc_subchannel_call** call) {
-  *call = static_cast<grpc_subchannel_call*>(gpr_arena_alloc(
-      args.arena, sizeof(grpc_subchannel_call) +
-                      channel_stack_->call_stack_size + args.parent_data_size));
+  size_t allocation_size =
+      GPR_ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(grpc_subchannel_call));
+  if (args.parent_data_size > 0) {
+    allocation_size +=
+        GPR_ROUND_UP_TO_ALIGNMENT_SIZE(channel_stack_->call_stack_size) +
+        args.parent_data_size;
+  } else {
+    allocation_size += channel_stack_->call_stack_size;
+  }
+  *call = static_cast<grpc_subchannel_call*>(
+      gpr_arena_alloc(args.arena, allocation_size));
   grpc_call_stack* callstk = SUBCHANNEL_CALL_TO_CALL_STACK(*call);
   RefCountedPtr<ConnectedSubchannel> connection =
       Ref(DEBUG_LOCATION, "subchannel_call");