lib: rework how we "override" assert()

The previous method, using zassert.h and hoping nothing includes
assert.h (which, on glibc at least, just does "#undef assert" and puts
its own definition in...) was fragile - and actually broke undetected.

Just provide our own assert.h and control overriding by putting it in a
separate directory to add to the include path (or not.)

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

1 files changed, 98 insertions, 0 deletions

diff --git a/lib/assert/assert.h b/lib/assert/assert.h
new file mode 100644
index 0000000000..fbdbd52ce8
--- /dev/null
+++ b/lib/assert/assert.h
@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2021  David Lamparter, for NetDEF, Inc.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* WARNING: this file is "special" in that it overrides the system-provided
+ * assert.h by being on the include path before it.  That means it should
+ * provide the functional equivalent.
+ *
+ * This is intentional because FRR extends assert() to write to the log and
+ * add backtraces.  Overriding the entire file is the simplest and most
+ * reliable way to get this to work;  there were problems previously with the
+ * system assert.h getting included afterwards and redefining assert() back to
+ * the system variant.
+ */
+
+#ifndef _FRR_ASSERT_H
+#define _FRR_ASSERT_H
+
+#include "xref.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef __cplusplus
+/* C++ has this built-in, but C provides it in assert.h for >=C11.  Since we
+ * replace assert.h entirely, we need to provide it here too.
+ */
+#define static_assert _Static_assert
+#endif
+
+struct xref_assert {
+	struct xref xref;
+
+	const char *expr;
+	const char *extra, *args;
+};
+
+extern void _zlog_assert_failed(const struct xref_assert *xref,
+				const char *extra, ...) PRINTFRR(2, 3)
+	__attribute__((noreturn));
+
+/* the "do { } while (expr_)" is there to get a warning for assignments inside
+ * the assert expression aka "assert(x = 1)".  The (necessary) braces around
+ * expr_ in the if () statement would suppress these warnings.  Since
+ * _zlog_assert_failed() is noreturn, the while condition will never be
+ * checked.
+ */
+#define assert(expr_)                                                          \
+	({                                                                     \
+		static const struct xref_assert _xref __attribute__(           \
+			(used)) = {                                            \
+			.xref = XREF_INIT(XREFT_ASSERT, NULL, __func__),       \
+			.expr = #expr_,                                        \
+		};                                                             \
+		XREF_LINK(_xref.xref);                                         \
+		if (__builtin_expect((expr_) ? 0 : 1, 0))                      \
+			do {                                                   \
+				_zlog_assert_failed(&_xref, NULL);             \
+			} while (expr_);                                       \
+	})
+
+#define assertf(expr_, extra_, ...)                                            \
+	({                                                                     \
+		static const struct xref_assert _xref __attribute__(           \
+			(used)) = {                                            \
+			.xref = XREF_INIT(XREFT_ASSERT, NULL, __func__),       \
+			.expr = #expr_,                                        \
+			.extra = extra_,                                       \
+			.args = #__VA_ARGS__,                                  \
+		};                                                             \
+		XREF_LINK(_xref.xref);                                         \
+		if (__builtin_expect((expr_) ? 0 : 1, 0))                      \
+			do {                                                   \
+				_zlog_assert_failed(&_xref, extra_,            \
+						    ##__VA_ARGS__);            \
+			} while (expr_);                                       \
+	})
+
+#define zassert assert
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _FRR_ASSERT_H */