Make printf weak and add libprintf_flt.a

This allows substituting a fully-featured printf that supports floating
point via -lprintf_flt, without blowing up the binaries for most
applications. This is the approach that AVR uses.

mos-platform/common/c/CMakeLists.txt

@@ -35,9 +35,13 @@ add_platform_library(common-c
 )
 # Prevent the implementation of libcalls from being reduced to a call of those libcalls.
 set_property(SOURCE mem.c PROPERTY COMPILE_OPTIONS -fno-builtin-memset)
-set_property(SOURCE printf.c PROPERTY COMPILE_DEFINITIONS
+set_property(TARGET common-c PROPERTY COMPILE_DEFINITIONS
   PRINTF_DISABLE_SUPPORT_FLOAT
   PRINTF_DISABLE_SUPPORT_EXPONENTIAL
+  PRINTF_WEAK
 )
 target_include_directories(common-c SYSTEM BEFORE PUBLIC ${INCLUDE_DIR})
 target_link_libraries(common-c PRIVATE common-asminc)
+
+add_platform_library(common-printf_flt printf.c)
+target_include_directories(common-printf_flt SYSTEM BEFORE PUBLIC ${INCLUDE_DIR})

mos-platform/common/c/printf.c

@@ -98,6 +98,12 @@
 #define PRINTF_SUPPORT_PTRDIFF_T
 #endif
 
+#if PRINTF_WEAK
+#define PRINTF_ATTR __attribute__((weak))
+#else
+#define PRINTF_ATTR
+#endif
+
 ///////////////////////////////////////////////////////////////////////////////
 
 // internal flag definitions
@@ -938,35 +944,35 @@ static int _vsnprintf(out_fct_type out, char *buffer, const size_t maxlen,
 
 ///////////////////////////////////////////////////////////////////////////////
 
-int printf(const char *format, ...) {
+PRINTF_ATTR int printf(const char *format, ...) {
   va_list va;
   va_start(va, format);
   const int ret = vprintf(format, va);
   va_end(va);
   return ret;
 }
 
-int sprintf(char *buffer, const char *format, ...) {
+PRINTF_ATTR int sprintf(char *buffer, const char *format, ...) {
   va_list va;
   va_start(va, format);
   const int ret = vsnprintf(buffer, (size_t)-1, format, va);
   va_end(va);
   return ret;
 }
 
-int snprintf(char *buffer, size_t count, const char *format, ...) {
+PRINTF_ATTR int snprintf(char *buffer, size_t count, const char *format, ...) {
   va_list va;
   va_start(va, format);
   const int ret = vsnprintf(buffer, count, format, va);
   va_end(va);
   return ret;
 }
 
-int vprintf(const char *format, va_list va) {
+PRINTF_ATTR int vprintf(const char *format, va_list va) {
   char buffer[1];
   return _vsnprintf(_out_char, buffer, (size_t)-1, format, va);
 }
 
-int vsnprintf(char *buffer, size_t count, const char *format, va_list va) {
+PRINTF_ATTR int vsnprintf(char *buffer, size_t count, const char *format, va_list va) {
   return _vsnprintf(_out_buffer, buffer, count, format, va);
 }