test-app: add dummy .data and .bss sections when using clang

Author: mattia-moffa

test-app/Makefile

@@ -114,6 +114,10 @@ ifeq ($(USE_CLANG),1)
   else
     OBJCOPY_IMAGE_FLAGS+=$(CLANG_ARM_OBJCOPY_FLASH_FLAGS_APP)
   endif
+  # Clang doesn't emit empty .data/.bss sections in object files (GCC does).
+  # GNU ld mishandles AT() for output sections with no matching input sections,
+  # setting LMA=VMA instead of the specified flash address.
+  APP_OBJS+=clang_sections.o
 endif
 
 ifeq ($(DEBUG_UART),1)

test-app/clang_sections.S

@@ -0,0 +1,8 @@
+/* Workaround for GNU ld mishandling AT() on output sections when no input
+ * object contributes a matching section.  Clang does not emit empty .data/.bss
+ * sections in object files (GCC does), so GNU ld fails to assign the correct
+ * LMA for the .data output section, producing a huge sparse binary.
+ * Including this object ensures .data and .bss exist as inputs.
+ */
+.section .data
+.section .bss