Dump faulting function PC in stack overflow

Report a fake exception to have the exception decoder print the actual
faulting function.  This won't tell you where in the function the issue
happened, but it will tell you the function name first and foremost.

Author: earlephilhower

cores/esp8266/core_esp8266_postmortem.cpp

@@ -45,6 +45,8 @@ static const char* s_panic_what = 0;
 static bool s_abort_called = false;
 static const char* s_unhandled_exception = NULL;
 
+static uint32_t s_stacksmash_addr = 0;
+
 void abort() __attribute__((noreturn));
 static void uart_write_char_d(char c);
 static void uart0_write_char_d(char c);
@@ -150,6 +152,8 @@ void __wrap_system_restart_local() {
     }
     else if (rst_info.reason == REASON_USER_STACK_SMASH) {
         ets_printf_P(PSTR("\nStack overflow detected.\n"));
+        ets_printf_P(PSTR("\nException (%d):\nepc1=0x%08x epc2=0x%08x epc3=0x%08x excvaddr=0x%08x depc=0x%08x\n"),
+            5 /* Alloca exception, closest thing to stack fault*/, s_stacksmash_addr, 0, 0, 0, 0);
    }
     else {
         ets_printf_P(PSTR("\nGeneric Reset\n"));
@@ -299,6 +303,8 @@ void __stack_chk_fail(void) {
     s_user_reset_reason = REASON_USER_STACK_SMASH;
     ets_printf_P(PSTR("\nPANIC: Stack overrun"));
 
+    s_stacksmash_addr = (uint32_t)__builtin_return_address(0);
+
     if (gdb_present())
         __asm__ __volatile__ ("syscall"); // triggers GDB when enabled