Catch missing printf implementation

ext/eyalroz/module.lb

@@ -19,7 +19,6 @@ def prepare(module, options):
 
 def build(env):
     env.collect(":build:path.include", "modm/ext")
-    env.collect(":build:ccflags", "-fno-builtin-printf")
     env.outbasepath = "modm/ext/printf"
 
     env.copy("printf/src/printf/printf.h", "printf.h")

ext/eyalroz/module.md

@@ -44,3 +44,24 @@ extern "C" void putchar_(char c)
     // MODM_LOG_INFO << c;
 }
 ```
+
+
+## printf is not implemented Error
+
+This module is not included by default and any attempt to use any of the printf
+methods fails with one or multiple linker error messages similiar to this:
+
+```
+`printf' referenced in section `.text.startup.main'
+    of main.o: defined in discarded section
+      `.printf_is_not_implemented!_
+           _Please_include_the__modm:printf__module_in_your_project!'
+    of libmodm.a(no_printf.o)
+```
+
+This is to prevent you from *accidentally* using the Newlib implementation of
+printf, which is very expensive and also dynamically allocated memory.
+You can either:
+
+1. Include this module, which provides a fast printf implementation.
+2. Provide your own implementation by strongly linking against printf functions.

ext/eyalroz/no_printf.c.in

@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2024, Niklas Hauser
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+// ----------------------------------------------------------------------------
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <modm/architecture/utils.hpp>
+
+// ----------------------------------------------------------------------------
+modm_weak modm_section("{{ no_printf_section }}")
+int vprintf(const char* format, va_list arg)
+{
+	(void) format;
+	(void) arg;
+	return 0;
+}
+
+modm_weak modm_section("{{ no_printf_section }}")
+int vsnprintf(char* s, size_t n, const char* format, va_list arg)
+{
+	(void) s;
+	(void) n;
+	(void) format;
+	(void) arg;
+	return 0;
+}
+
+modm_weak modm_section("{{ no_printf_section }}")
+int vsprintf(char* s, const char* format, va_list arg)
+{
+	(void) s;
+	(void) format;
+	(void) arg;
+	return 0;
+}
+
+modm_weak modm_section("{{ no_printf_section }}")
+int vfctprintf(void (*out)(char c, void* extra_arg), void* extra_arg, const char* format, va_list arg)
+{
+	(void) out;
+	(void) extra_arg;
+	(void) format;
+	(void) arg;
+	return 0;
+}
+
+modm_weak modm_section("{{ no_printf_section }}")
+int printf(const char* format, ...)
+{
+	(void) format;
+	return 0;
+}
+
+modm_weak modm_section("{{ no_printf_section }}")
+int sprintf(char* s, const char* format, ...)
+{
+	(void) s;
+	(void) format;
+	return 0;
+}
+
+modm_weak modm_section("{{ no_printf_section }}")
+int snprintf(char* s, size_t n, const char* format, ...)
+{
+	(void) s;
+	(void) n;
+	(void) format;
+	return 0;
+}
+
+modm_weak modm_section("{{ no_printf_section }}")
+int fctprintf(void (*out)(char c, void* extra_arg), void* extra_arg, const char* format, ...)
+{
+	(void) out;
+	(void) extra_arg;
+	(void) format;
+	return 0;
+}

src/modm/platform/core/cortex/linker.macros

@@ -231,14 +231,8 @@ MAIN_STACK_SIZE = {{ options[":platform:cortex-m:main_stack_size"] }};
 		. = ALIGN(4);
 		__assertion_table_end = .;
 	} >{{memory}}
-
-	/* We do not call static destructors ever */
-	/DISCARD/ :
-	{
-		*(.fini_array .fini_array.*)
-	}
-	%% if with_cpp_exceptions
 	%#
+	%% if with_cpp_exceptions
 	/* C++ exception unwind tables */
 	.exidx :
 	{
@@ -257,24 +251,27 @@ MAIN_STACK_SIZE = {{ options[":platform:cortex-m:main_stack_size"] }};
 
 	/* required by libc __libc_fini_array, but never called */
 	_fini = .;
-	%% else
-	%#
-	/* C++ exception unwind tables are discarded */
+	%% endif
+
 	/DISCARD/ :
 	{
+		/* We do not call static destructors ever */
+		*(.fini_array .fini_array.*)
+		%% if not with_cpp_exceptions
+		/* C++ exception unwind tables are discarded */
 		*(.ARM.extab* .gnu.linkonce.armextab.*)
 		*(.ARM.exidx* .gnu.linkonce.armexidx.*)
 		*(.eh_frame*)
-	}
-	%% endif
-	%% if not with_heap
-	%#
-	/* Catch use of dynamic memory without `modm:platform:heap` module. */
-	/DISCARD/ :
-	{
+		%% endif
+		%% if not with_heap
+		/* Catch use of dynamic memory without `modm:platform:heap` module. */
 		*({{no_heap_section}})
+		%% endif
+		%% if not with_printf
+		/* Catch use of printf without `modm:printf` module. */
+		*({{no_printf_section}})
+		%% endif
 	}
-	%% endif
 %% endmacro
 
 

src/modm/platform/core/cortex/module.lb

@@ -127,6 +127,11 @@ def common_memories(env):
 # See :platform:heap for explanation
 common_no_heap_section = (".Heap_is_not_implemented!__"
         "Please_include_the__modm:platform:heap__module_in_your_project!")
+# See :printf for explanation
+common_no_printf_section = (".printf_is_not_implemented!__"
+        "Please_include_the__modm:printf__module_in_your_project!")
+
+
 
 def common_linkerscript(env):
     """
@@ -170,8 +175,10 @@ def common_linkerscript(env):
 
         "with_cpp_exceptions": env.get(":stdc++:exceptions", False),
         "with_heap": env.has_module(":platform:heap"),
+        "with_printf": env.has_module(":printf"),
         "with_crashcatcher": env.has_module(":crashcatcher"),
         "no_heap_section": common_no_heap_section,
+        "no_printf_section": common_no_printf_section,
     }
     properties.update(common_memories(env))
     return properties
@@ -336,6 +343,11 @@ def build(env):
     if not env.has_module(":platform:heap"):
         env.substitutions["no_heap_section"] = common_no_heap_section
         env.template("../../heap/cortex/no_heap.c.in", "no_heap.c")
+    # Deprecate printf functions if not implemented!
+    env.collect(":build:ccflags", "-fno-builtin-printf")
+    if not env.has_module(":printf"):
+        env.substitutions["no_printf_section"] = common_no_printf_section
+        env.template(repopath("ext/eyalroz/no_printf.c.in"), "no_printf.c")
 
     if env.has_module(":architecture:atomic"):
         env.template("atomic_lock_impl.hpp.in")