Build Systems & Toolchain

Q1. (4 marks — 1 each)

1. Preprocessing — expands #include, macros, conditionals → produces preprocessed source (.i). (1)
2. Compilation — translates C/C++ into assembly → produces assembly (.s). (1)
3. Assembly — assembler converts assembly to machine code → produces object file (.o). (1)
4. Linking — combines object files and libraries, resolves symbols → produces executable. (1)

Q2. (4 marks — 1 each) (a) .o → (iii) relocatable object file (b) .a → (i) static library archive (c) .so → (ii) shared/dynamic library (d) .i → (iv) preprocessed source

Q3. (4 marks) (a) Symbol table — a list of symbols (functions/variables) defined and referenced by the object, recording their names, whether they are defined here or external, and their section/offset. (2) (b) Relocation entry — a record telling the linker which locations in the code/data must be patched with final addresses once symbols are placed, i.e. it fixes up references whose addresses aren't known until link time. (2)

Q4. (5 marks)

• Advantage (any one): smaller executables; library shared in memory across processes; can update the library without relinking. (1.5)
• Disadvantage (any one): runtime dependency (must be present/found at load time); slight load-time/indirection overhead; version/"DLL hell" issues. (1.5)
• PIC = Position-Independent Code. (1)
• Needed because a shared library may be loaded at any address in different processes; PIC uses relative addressing (e.g. via GOT/PLT) so the code works regardless of load address without per-load relocation of the code segment. (1)

Q5. (4 marks)

• Why: Linkers process inputs left to right; when libutil.a is seen first, no unresolved symbols exist yet, so the linker pulls nothing from the archive. Then main.o introduces a reference to func, but the archive has already been passed → undefined reference. Order matters: libraries must come after the objects that use them. (2)
• Corrected command: (2)

gcc main.o libutil.a -o prog

Q6. (6 marks — 1 for name + 1 for value each)

• $@ = the target name → value prog. (2)
• $< = the first prerequisite → value main.o. (2)
• $^ = all prerequisites (deduplicated) → value main.o util.o. (2)

Q7. (4 marks) (a) A phony target is one that does not represent an actual file; declared with .PHONY: so make always runs its recipe (won't be skipped even if a file of that name exists). (2) (b) (2)

.PHONY: clean
clean:
	rm -f *.o prog

Q8. (5 marks — 1 each) (a) -O0 — no optimization (default, fastest compile, best for debugging). (b) -O2 — enable a broad set of optimizations for speed without excessive code size. (c) -Wall — enable common/recommended warning messages. (d) -g — emit debug information (symbols, line numbers) for use by GDB. (e) -fsanitize=address — instrument with AddressSanitizer to detect memory errors (buffer overflows, use-after-free) at runtime.

Q9. (4 marks — 1 each) (a) AddressSanitizer (ASan) — -fsanitize=address (b) ThreadSanitizer (TSan) — -fsanitize=thread (c) UndefinedBehaviorSanitizer (UBSan) — -fsanitize=undefined (d) objdump (e.g. objdump -d)

[
  {"claim":"There are exactly 4 classic compilation stages listed in Q1","code":"stages=['preprocess','compile','assemble','link']; result = (len(stages)==4)"},
  {"claim":"Q6 automatic variable values: $@=prog, $<=main.o, $^ joins all prereqs","code":"target='prog'; prereqs=['main.o','util.o']; at=target; first=prereqs[0]; allp=' '.join(prereqs); result = (at=='prog' and first=='main.o' and allp=='main.o util.o')"},
  {"claim":"Correct link order places objects before archives (main.o then libutil.a)","code":"order=['main.o','libutil.a']; result = order.index('main.o') < order.index('libutil.a')"},
  {"claim":"Q8 has 5 flags mapped one-to-one","code":"flags={'-O0','-O2','-Wall','-g','-fsanitize=address'}; result = (len(flags)==5)"}
]