Disassemble the OS (use a compact representation for repetitive parts), re-assemble and check that the result is identical.

example-os/.gitignore

@@ -1 +1,4 @@
-/os.sh
+/os.sh
+/os.ndisasm.disasm
+/os.reasm.asm
+/os.reasm

example-os/Makefile

@@ -1,5 +1,5 @@
 .PHONY: all
-all: os.sh
+all: os.sh os.ndisasm.disasm os.reasm.asm os.reasm
 
 ../deploy-screenshots:
 	mkdir $@
@@ -8,6 +8,28 @@ os.sh: os.asm ../deploy-screenshots Makefile
 	nasm -o $@ $<
 	chmod a+x $@
 
+os.ndisasm.disasm: os.sh Makefile
+	ndisasm $< \
+        | uniq -s 8 -c \
+        | sed -r -e 's/\s*1 //; t; s/\s*([0-9]+) ([^ ]+\s+[^ ]+\s+)/\2times \1 /' \
+        | sed -r -e 's/([^ ]+\s+[0-9A-F]{4}\s+jz) 0x/\1 short 0x/' > $@
+#         The last sed line just above fixes an issue with ndisasm
+#         (it fails to annotate the jz with short).
+
+os.reasm.asm: os.ndisasm.disasm Makefile
+	sed -r -e 's/^[^ ]+ +[^ ]+ +//' $< > $@
+
+os.reasm: os.reasm.asm os.sh Makefile
+	nasm $< -o $@
+	@echo "diff $@ os.sh"
+	@diff $@ os.sh \
+         && echo "Re-assembled file is identical to os.sh" \
+         || (echo "Re-assembled file is different from os.sh"; exit 1)
+
+.PHONY: clean Makefile
+clean:
+	rm -f os.sh os.ndisasm.disasm os.reasm.asm os.reasm
+
 .PHONY: test
 test: test-qemu-system-i386 test-qemu-system-arm test-virtualbox test-bochs Makefile