Use miminal config file and bare-bone custom CRT.

Makefile

@@ -1,6 +1,7 @@
+PROJECT := demo
+
 SRC = \
 	  src/ceda_print.c		\
-	  src/entrypoint.c		\
 	  src/main.c 			\
 	  \
 
@@ -10,11 +11,14 @@ ECHO	:=	@echo
 QUIET	:=	@
 OUTDIR	:=	build
 
-$(OUTDIR)/main.prg: $(OUTDIR)/main.rom
+$(OUTDIR)/$(PROJECT).prg: $(OUTDIR)/$(PROJECT)_code_compiler.bin
-	dd if=$< of=$@ bs=1 seek=2
+	echo -n -e '\x00\x10' > $@
+	cat $< >> $@
 
-$(OUTDIR)/main.rom: $(OBJ) | $(OUTDIR)
+$(OUTDIR)/$(PROJECT)_code_compiler.bin: $(OBJ) | $(OUTDIR)
-	zcc +z80 -create-app --no-crt -m -o $@ $?
+	zcc +conf.cfg \
+		-crt0=src/crt.asm \
+		-m -o $(OUTDIR)/$(PROJECT) $?
 
 %.o: %.c
 	zcc +z80 -c -o $@ $<

src/crt.asm

@@ -1,9 +1,13 @@
+SECTION code_compiler
+    org $1000
+
 EXTERN _main
 
-entrypoint:
+PUBLIC __Start
+
+__Start:
     ld sp,0xc000
 
     call _main
 
     jp ASMPC
-

src/main.c

@@ -1,8 +1,9 @@
 #include "ceda_print.h"
 
+int globalvar = 0x7777;
+
 int main(void) {
     ceda_print("Hello world!");
 
     return 0;
 }
-