sys/newlib_syscalls_default: wrap newlib's assert implementation

This avoids inconsistent output when external code gets linked in that
directly links against newlib's assert implementation (e.g. binary blobs
or packages that do not add `core/lib/include` to the include paths).

This also greatly benefits wrapping printf, as newlib's `__assert_func()`
directly links to internal printf functions of newlib.

Co-authored-by: crasbe <[email protected]>

Author: maribu

makefiles/libc/newlib.mk

@@ -100,3 +100,7 @@ ifeq (1,$(USE_NEWLIB_NANO))
      INCLUDES := -isystem $(NEWLIB_NANO_INCLUDE_DIR) $(INCLUDES)
   endif
 endif
+
+# In case externally compiled code gets linked in, it may use newlib's assert
+# implementation. We wrap that to RIOT's assert implementation for consistency.
+LINKFLAGS += -Wl,-wrap=__assert_func

pkg/mpaland-printf/Makefile.include

@@ -19,6 +19,10 @@ LINKFLAGS += -Wl,-wrap=puts
 # stdio, we will catch any instance of both mpaland-printf and newlib's stdio
 # being both linked in.
 LINKFLAGS += -Wl,-wrap=_printf_common
+LINKFLAGS += -Wl,-wrap=_fprintf_r
+LINKFLAGS += -Wl,-wrap=_printf_r
+LINKFLAGS += -Wl,-wrap=iprintf
+LINKFLAGS += -Wl,-wrap=fiprintf
 
 # Workaround for bug in the newlib headers shipped with e.g. Ubuntu 24.04 LTS
 # not defining PRId64 / PRIu64 / PRIx64 / PRIo64 in <inttypes.h> due to an issue

sys/newlib_syscalls_default/syscalls.c

@@ -34,6 +34,7 @@
 #include <sys/unistd.h>
 #include <unistd.h>
 
+#include "assert.h"
 #include "log.h"
 #include "modules.h"
 #include "periph/pm.h"
@@ -646,3 +647,20 @@ clock_t _times_r(struct _reent *ptr, struct tms *ptms)
 
     return (-1);
 }
+
+/**
+ * @brief Wrapper for newlib's assert implementation
+ */
+NORETURN
+void __wrap___assert_func (const char *file, int line, const char *func, const char *expr)
+{
+    (void)file;
+    (void)line;
+    (void)func;
+    (void)expr;
+#ifdef DEBUG_ASSERT_VERBOSE
+    _assert_failure(file, line);
+#else
+    _assert_panic();
+#endif
+}