Demonstrate how to trick llvm scan-build's core.StackAddressEscape

Author: Craig Ringer

c/clang_return_stack_checks/.gitignore

@@ -7,4 +7,5 @@ sigjmp_escape_noinner
 sigjmp_escape_noinner_fake*
 sigjmp_escape_hdr
 sigjmp_escape_inner_pop
+mask_local_escape
 scan-build-*/

c/clang_return_stack_checks/Makefile

@@ -47,8 +47,11 @@ sigjmp_escape_hdr: sigjmp_escape_hdr.c sigjmp_escape_hdr_try.c | tmpdir
 	$(CC) $(CFLAGS) -DUSE_FINALLY -c sigjmp_escape_hdr.c -o sigjmp_escape_hdr.o
 	$(CC) $(CFLAGS_LINK) sigjmp_escape_hdr.o sigjmp_escape_hdr_try.o -o $@
 
+mask_local_escape: mask_local_escape.c | tmpdir
+	$(CC) $(CFLAGS) $< -o $@
+
 clean:
-	rm -f *.o guard.so return_stack_escape sigjmp_escape sigjmp_escape_fake* sigjmp_escape_guard sigjmp_escape_guard_fake* sigjmp_escape_guard_inner_pop sigjmp_escape_hdr
+	rm -f *.o guard.so return_stack_escape sigjmp_escape sigjmp_escape_fake* sigjmp_escape_guard sigjmp_escape_guard_fake* sigjmp_escape_guard_inner_pop sigjmp_escape_hdr mask_local_escape
 	rm -rf scan-build-*
 
 run_return_stack_escape: return_stack_escape
@@ -67,6 +70,9 @@ run_sigjmp_escape_hdr: sigjmp_escape_hdr
 	if ./sigjmp_escape_hdr 0 1; then exit 1; fi
 	./sigjmp_escape_hdr 1 1
 
-run: run_return_stack_escape run_sigjmp_escape run_sigjmp_escape_hdr
+run_mask_local_escape: mask_local_escape
+	./mask_local_escape
+
+run: run_return_stack_escape run_sigjmp_escape run_sigjmp_escape_hdr run_mask_local_escape
 
 check: run

c/clang_return_stack_checks/mask_local_escape.c

@@ -0,0 +1,63 @@
+/*
+ * Demonstrate how to trick llvm scan-build's core.StackAddressEscape checker
+ * via simple indirection.
+ */
+
+#include <stdio.h>
+#include <assert.h>
+
+struct chain_container {
+	int * leaky_member;
+	struct chain_container * previous;
+};
+
+struct chain_container * sneaky_chain_container = 0;
+
+void
+escape_via_sneaky_chain_assignment_1(void)
+{
+	struct chain_container new_entry = {0,0};
+	int g = 1;
+	fprintf(stderr, "&g = %p\n", &g);
+	/* g escapes into global scope */
+	sneaky_chain_container->leaky_member = &g;
+	/* Pointer to container is replaced with indirect pointer via chain */
+	new_entry.previous = sneaky_chain_container;
+	sneaky_chain_container = &new_entry;
+
+	/*
+	 * Restore container pointer from caller.
+	 *
+	 * scan-build has lost track of &g in its leaky_member now.
+	 */
+	sneaky_chain_container = sneaky_chain_container->previous;
+
+	/* even though we definitely leak it */
+	assert(sneaky_chain_container->leaky_member == &g);
+}
+
+void
+escape_via_sneaky_chain_assignment(void)
+{
+	struct chain_container parent_sneaky = {0,0};
+	sneaky_chain_container = &parent_sneaky;
+	escape_via_sneaky_chain_assignment_1();
+	/*
+	 * pointer to auto variable from escape_via_sneaky_chain_assignment_1
+	 * has escaped. Dereferencing it would be a memory error.
+	 */
+	fprintf(stderr, "&g has escaped: %p\n",
+			sneaky_chain_container->leaky_member);
+
+	/*
+	 * Ensure we don't complain about &parent_sneaky escaping.
+	 */
+	sneaky_chain_container = 0;
+}
+
+int
+main(void)
+{
+	escape_via_sneaky_chain_assignment();
+	return 0;
+}