Assert that file IO is not used in ISRs

Trigger an assert if a file is read from or written to from an
interrupt handler or critical section. This includes using printf
from an interrupt handler or critical section. This makes failures
due to use in incorrect context deterministic and easier to locate.

This feature is enabled by defining MBED_TRAP_ERRORS_ENABLED to 1 or
by using the debug profile.

Author: c1728p9

platform/mbed_retarget.cpp

@@ -23,6 +23,7 @@
 #include "platform/PlatformMutex.h"
 #include "platform/mbed_error.h"
 #include "platform/mbed_stats.h"
+#include "platform/mbed_critical.h"
 #if MBED_CONF_FILESYSTEM_PRESENT
 #include "filesystem/FileSystem.h"
 #include "filesystem/File.h"
@@ -309,6 +310,12 @@ extern "C" int PREFIX(_write)(FILEHANDLE fh, const unsigned char *buffer, unsign
 #endif
     int n; // n is the number of bytes written
 
+#if defined(MBED_TRAP_ERRORS_ENABLED) && MBED_TRAP_ERRORS_ENABLED
+    if (core_util_is_isr_active() || !core_util_are_interrupts_enabled()) {
+        error("Error - writing to a file in an ISR or critical section\r\n");
+    }
+#endif
+
     if (fh < 3) {
 #if DEVICE_SERIAL
         if (!stdio_uart_inited) init_serial();
@@ -353,6 +360,12 @@ extern "C" int PREFIX(_read)(FILEHANDLE fh, unsigned char *buffer, unsigned int
 #endif
     int n; // n is the number of bytes read
 
+#if defined(MBED_TRAP_ERRORS_ENABLED) && MBED_TRAP_ERRORS_ENABLED
+    if (core_util_is_isr_active() || !core_util_are_interrupts_enabled()) {
+        error("Error - reading from a file in an ISR or critical section\r\n");
+    }
+#endif
+
     if (fh < 3) {
         // only read a character at a time from stdin
 #if DEVICE_SERIAL