Harden Print::printf() method

based on @PaulStoffregen works for Teensyduino:
https://github.com/PaulStoffregen/cores

Remove PRINTF_BUFFER usage.
Aligned declaration with `printf()` one by returning the number
of characters printed (excluding the null byte used to end output
to strings).

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

cores/arduino/Print.cpp

@@ -21,8 +21,8 @@
  */
 
 #include <stdlib.h>
-#include <stdio.h>
 #include <string.h>
+#include <unistd.h>
 #include <math.h>
 #include "Arduino.h"
 
@@ -196,24 +196,42 @@ size_t Print::println(const Printable &x)
   return n;
 }
 
-void Print::printf(const char *format, ...)
+extern "C" {
+  __attribute__((weak))
+  int _write(int file, char *ptr, int len)
+  {
+#ifdef HAL_UART_MODULE_ENABLED
+    switch (file) {
+      case STDOUT_FILENO:
+      case STDERR_FILENO:
+        uart_debug_write((uint8_t *)ptr, (uint32_t)len);
+        break;
+      case STDIN_FILENO:
+        break;
+      default:
+        ((class Print *)file)->write((uint8_t *)ptr, len);
+        break;
+    }
+#else
+    (void)file;
+    (void)ptr;
+#endif
+    return len;
+  }
+}
+
+int Print::printf(const char *format, ...)
 {
-  char buf[PRINTF_BUFFER];
   va_list ap;
   va_start(ap, format);
-  vsnprintf(buf, sizeof(buf), format, ap);
-  write(buf);
-  va_end(ap);
+  return vdprintf((int)this, format, ap);
 }
 
-void Print::printf(const __FlashStringHelper *format, ...)
+int Print::printf(const __FlashStringHelper *format, ...)
 {
-  char buf[PRINTF_BUFFER];
   va_list ap;
   va_start(ap, format);
-  vsnprintf_P(buf, sizeof(buf), (const char *)format, ap);
-  write(buf);
-  va_end(ap);
+  return vdprintf((int)this, (const char *)format, ap);
 }
 
 // Private Methods /////////////////////////////////////////////////////////////

cores/arduino/Print.h

@@ -32,10 +32,6 @@
 #define OCT 8
 #define BIN 2
 
-#ifndef PRINTF_BUFFER
-#define PRINTF_BUFFER 80
-#endif
-
 // uncomment next line to support printing of 64 bit ints.
 #define SUPPORT_LONGLONG
 
@@ -109,8 +105,8 @@ class Print {
     void print(uint64_t, uint8_t = DEC);
 #endif
 
-    void printf(const char *format, ...);
-    void printf(const __FlashStringHelper *format, ...);
+    int printf(const char *format, ...);
+    int printf(const __FlashStringHelper *format, ...);
 };
 
 #endif

libraries/SrcWrapper/src/syscalls.c

@@ -81,16 +81,12 @@ int _read(UNUSED(int file), UNUSED(char *ptr), UNUSED(int len))
   return 0;
 }
 
+/* Moved to Print.cpp to support Print::printf()
 __attribute__((weak))
 int _write(UNUSED(int file), char *ptr, int len)
 {
-#ifdef HAL_UART_MODULE_ENABLED
-  return uart_debug_write((uint8_t *)ptr, (uint32_t)len);
-#else
-  (void)ptr;
-  return len;
-#endif
 }
+*/
 
 __attribute__((weak))
 void _exit(UNUSED(int status))