[PATCH] Add check_all_func_returns

This replaces functionality in "lint" that checked every function with a
non-void return is handled.

We cannot use GCC's functionality for this, since a "(void)" cast is not
sufficient to turn it off, and besides, we want this to be the default for
everything.
---
 check_all_func_returns.c | 88 ++++++++++++++++++++++++++++++++++++++++
 check_list.h             |  3 ++
 2 files changed, 91 insertions(+)
 create mode 100644 check_all_func_returns.c

diff --git a/check_all_func_returns.c b/check_all_func_returns.c
new file mode 100644
index 00000000..f9d77449
--- /dev/null
+++ b/check_all_func_returns.c
@@ -0,0 +1,88 @@
+/*
+ * Copyright 2018 Joyent, Inc.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
+ */
+
+/*
+ * Like lint of old, check that every return value from every function is used.
+ * Casting to (void) will silence this check.
+ */
+
+#include "smatch.h"
+#include "smatch_slist.h"
+
+static void check_func_return(struct expression *expr)
+{
+	struct symbol *sym = get_real_base_type(get_type(expr->fn));
+	const char *func = expr_to_str(expr->fn);
+	struct statement *stmt;
+
+	if (sym == NULL) {
+		sm_error("unknown type for func '%s'", func);
+		return;
+	}
+
+	if (expr->type != EXPR_CALL) {
+		sm_error("func '%s' is not a call site", func);
+		return;
+	}
+
+	/*
+	 * There is never any need to check these returns.
+	 */
+	if (strcmp(func, "memcpy") == 0 ||
+	    strcmp(func, "memmove") == 0 ||
+	    strcmp(func, "memset") == 0)
+		return;
+
+	/*
+	 * Closer to a policy here, but there seems very few cases where it's
+	 * useful to check the return value of the standard printf() family
+	 * outputting to stdout or stderr.
+	 */
+	if (strcmp(func, "printf") == 0 || strcmp(func, "vprintf") == 0)
+		return;
+
+	if (strcmp(func, "fprintf") == 0 || strcmp(func, "vfprintf")) {
+		const char *arg0 = expr_to_str(get_argument_from_call_expr(expr->args, 0));
+
+		if (arg0 != NULL &&
+		    (strcmp(arg0, "(&__iob[1])") == 0 ||
+		    strcmp(arg0, "(&__iob[2])") == 0))
+			return;
+	}
+
+	/*
+	 * Either we got the return type already (direct call),
+	 * or we need to go one further (function pointer call)
+	 */
+	if (sym == &void_ctype || (sym->type == SYM_FN &&
+		get_real_base_type(sym) == &void_ctype))
+		return;
+
+	stmt = last_ptr_list((struct ptr_list *)big_statement_stack);
+
+	if (stmt->type == STMT_EXPRESSION && stmt->expression == expr)
+		sm_error("unchecked function return '%s'", expr_to_str(expr->fn));
+}
+
+void check_all_func_returns(int id)
+{
+	if (option_project != PROJ_ILLUMOS_KERNEL &&
+	    option_project != PROJ_ILLUMOS_USER)
+		return;
+
+	add_hook(&check_func_return, FUNCTION_CALL_HOOK);
+}
diff --git a/check_list.h b/check_list.h
index 564bd1c2..cc3ce853 100644
--- a/check_list.h
+++ b/check_list.h
@@ -198,6 +198,9 @@ CK(check_wine_WtoA)
 
 CK(check_arm64_tagged)
 
+/* illumos specific */
+CK(check_all_func_returns)
+
 #include "check_list_local.h"
 
 CK(register_scope)
-- 
2.17.1