From 4f686b76145fef7e23f0dde7d6e9715ea806a8a1 Mon Sep 17 00:00:00 2001
From: Manu Evans <turkeyman@gmail.com>
Date: Wed, 12 Aug 2026 01:12:43 +1000
Subject: [PATCH] build: rebuild when the compile command changes

Record COMPILE_CMD in the object directory and make the target depend on it. Flag-only changes now invalidate an existing binary without forcing every invocation to rebuild.
---
 Makefile | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 6a0b31c6..b1557faf 100644
--- a/Makefile
+++ b/Makefile
@@ -269,6 +269,15 @@ endif
 # Note: LDC's -deps format is its own (D module deps), not Make-compatible --
 # so we don't `-include $(DEPFILE)`; full rebuild on file changes.
 
+# Recompile when flags or other compile-command inputs change.
+FLAGS_STAMP := $(OBJDIR)/build-flags
+
+# Parse-time refresh preserves normal timestamp behaviour under -n and -q.
+$(shell mkdir -p $(OBJDIR); \
+        printf '%s\n' '$(COMPILE_CMD)' > $(FLAGS_STAMP).new; \
+        cmp -s $(FLAGS_STAMP).new $(FLAGS_STAMP) || mv -f $(FLAGS_STAMP).new $(FLAGS_STAMP); \
+        rm -f $(FLAGS_STAMP).new)
+
 # =======================================================================
 # Build rules
 # =======================================================================
@@ -290,7 +299,7 @@ endif
 
 # -- Main target -------------------------------------------------------
 
-$(TARGET): $(SOURCES) $(BAREMETAL_OBJS) $(VENDOR_OBJS) $(BK_BEKEN_LIB)
+$(TARGET): $(SOURCES) $(BAREMETAL_OBJS) $(VENDOR_OBJS) $(BK_BEKEN_LIB) $(FLAGS_STAMP)
 
 # -- BK7231 FreeRTOS build (must come after $(TARGET) so it doesn't become default goal)