test(generate): lock in init_module vs finit_module classification

Audit of init_module (man 2 init_module) confirmed the implementation is
correct: init_module(void *module_image, unsigned long len, const char
*param_values) is classified KindModule (null_event), capturing neither
an fd nor a path — param_values is a module-parameter string, not a
filesystem path. finit_module(int fd, ...) is classified KindFd via
field-based matching and captures fd = args[0]. Both syscalls live in the
Security family and match docs/syscall-tracing-plan.md.

No explicit finit_module test or init_module-vs-finit_module distinction
test existed, so add lock-in coverage:
- testdata.go: real-layout Format constants for (f)init_module enter/exit.
- classify_test.go: assert init_module=KindModule with no PathnameField
  and finit_module=KindFd.
- codegen_test.go: assert generated BPF C for init_module captures no fd
  and no filename/path, while finit_module captures fd = args[0].

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/internal/generate/codegen_test.go b/internal/generate/codegen_test.go
index 746aa07..6b19129 100644
--- a/internal/generate/codegen_test.go
+++ b/internal/generate/codegen_test.go
@@ -24,6 +24,30 @@ func TestGenerateFdHandler(t *testing.T) {
 	requireContains(t, output, "#define SYS_ENTER_READ 844")
 }
 
+// TestGenerateModuleHandlers locks in the generated BPF C for the module-load
+// syscalls (man 2 init_module). init_module is a null_event: it must capture no
+// fd and no path/filename (its param_values arg is a parameter string, not a
+// path). finit_module is an fd_event capturing fd = args[0].
+func TestGenerateModuleHandlers(t *testing.T) {
+	initOut := generateFromPair(t, FormatInitModule, FormatExitInitModule)
+	requireContains(t, initOut, `SEC("tracepoint/syscalls/sys_enter_init_module")`)
+	requireContains(t, initOut, "struct null_event *ev = bpf_ringbuf_reserve(&event_map, sizeof(struct null_event), 0);")
+	requireContains(t, initOut, "ev->event_type = ENTER_NULL_EVENT;")
+	// init_module must not capture an fd or any filename/path.
+	if strings.Contains(initOut, "ev->fd =") {
+		t.Error("init_module handler must not capture an fd")
+	}
+	if strings.Contains(initOut, "ev->filename") || strings.Contains(initOut, "bpf_probe_read_user_str") {
+		t.Error("init_module handler must not capture param_values as a path/filename")
+	}
+
+	finitOut := generateFromPair(t, FormatFinitModule, FormatExitFinitModule)
+	requireContains(t, finitOut, `SEC("tracepoint/syscalls/sys_enter_finit_module")`)
+	requireContains(t, finitOut, "struct fd_event *ev = bpf_ringbuf_reserve(&event_map, sizeof(struct fd_event), 0);")
+	requireContains(t, finitOut, "ev->event_type = ENTER_FD_EVENT;")
+	requireContains(t, finitOut, "ev->fd = (__s32)ctx->args[0];")
+}
+
 func TestGeneratePidfdGetfdHandlerUsesPidfdArgument(t *testing.T) {
 	output := generateFromPair(t, FormatPidfdGetfd, FormatExitPidfdGetfd)