Add gdb stub library

Author: igrr

hardware/esp8266com/esp8266/cores/esp8266/core_esp8266_main.cpp

@@ -129,8 +129,12 @@ static void do_global_ctors(void) {
         (*p)();
 }
 
+extern "C" void __gdb_init() {}
+extern "C" void gdb_init(void) __attribute__ ((weak, alias("__gdb_init")));
+
 void init_done() {
     system_set_os_print(1);
+    gdb_init();
     do_global_ctors();
     esp_schedule();
 }

hardware/esp8266com/esp8266/cores/esp8266/core_esp8266_postmortem.c

@@ -31,7 +31,7 @@ extern void __real_system_restart_local();
 extern cont_t g_cont;
 
 
-static void uart_write_char_d(char c);
+void uart_write_char_d(char c);
 static void uart0_write_char_d(char c);
 static void uart1_write_char_d(char c);
 static void print_stack(uint32_t start, uint32_t end);
@@ -133,16 +133,16 @@ void uart_write_char_d(char c) {
     uart1_write_char_d(c);
 }
 
-void uart0_write_char_d(char c) {
-    while (((USS(0) >> USTXC) & 0xff) >= 0x7e) { }
+static void uart0_write_char_d(char c) {
+    while (((USS(0) >> USTXC) & 0xff)) { }
 
     if (c == '\n') {
         USF(0) = '\r';
     }
     USF(0) = c;
 }
 
-void uart1_write_char_d(char c) {
+static void uart1_write_char_d(char c) {
     while (((USS(1) >> USTXC) & 0xff) >= 0x7e) { }
 
     if (c == '\n') {

hardware/esp8266com/esp8266/libraries/GDBStub/README.md

@@ -0,0 +1,49 @@
+## Using GDB stub
+
+- Add `#include <GDBStub.h>` to the sketch
+- Upload the sketch
+- Redirect serial port to TCP port:
+```
+    tcp_serial_redirect.py -p /dev/tty.SLAB_USBtoUART -b 115200 --spy -P 9980 --rts=0 --dtr=0
+```
+Change port and baud rate as necessary. This command requires python and pyserial.
+- Observe serial output:
+```
+    nc localhost 9980
+```
+- When crash happens, `Trap %d: pc=%p va=%p` line will appear in serial output.
+- Close nc and start gdb:
+```
+    xtensa-lx106-elf-gdb /path/to/Sketch.cpp.elf -ex "target remote :9980"
+```
+- Use gdb to inspect program state at the point of an exception.
+
+## Tips and tricks
+
+- To halt the target when software WDT fires, add
+```
+    ((int*)0) = 0;
+```
+at the top of `__wrap_system_restart_local` in core_esp8266_postmortem.c.
+
+## License
+
+GDB Server stub by Marko Mikulicic was taken from Cesanta's smart.js
+
+https://github.com/cesanta/smart.js
+
+Copyright (c) 2013-2014 Cesanta Software Limited
+All rights reserved
+
+This software is dual-licensed: you can redistribute it and/or modify
+it under the terms of the GNU General Public License version 2 as
+published by the Free Software Foundation. For the terms of this
+license, see <http://www.gnu.org/licenses>.
+
+You are free to use this software under the terms of the GNU General
+Public License, but WITHOUT ANY WARRANTY; without even the implied
+warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+See the GNU General Public License for more details.
+
+Alternatively, you can license this software under a commercial
+license, as set out in <https://www.cesanta.com/license>.

hardware/esp8266com/esp8266/libraries/GDBStub/library.properties

@@ -0,0 +1,9 @@
+name=GDBStub
+version=0.1
+author=Marko Mikulicic (Cesanta)
+maintainer=Ivan Grokhotkov <[email protected]>
+sentence=GDB server stub from Cesanta's Smart.js
+paragraph=GDB server stub helps debug crashes when JTAG isn't an option.
+category=Uncategorized
+url=https://github.com/cesanta/smart.js
+architectures=esp8266