Fix 'corrupt stack?' warning in GDB backtrace (#1665)

* Fix 'corrupt stack?' warning in GDB backtrace

One cause is missing symbols, so tell GDB about ESP8266 ROM symbols defined in `bootrom.elf` file.

See https://github.com/jcmvbkbc/esp-elf-rom for how the `bootrom.elf` file was created.

Sming/Makefile-rboot.mk

@@ -50,6 +50,8 @@ RBOOT_E2_SECTS     ?= .text .data .rodata
 RBOOT_E2_USER_ARGS ?= -quiet -bin -boot2
 # GDB path
 GDB ?= $(ESP_HOME)/xtensa-lx106-elf/bin/xtensa-lx106-elf-gdb
+# File containing boot ROM debug symbols for GDB
+BOOTROM_ELF := bootrom.elf
 
 ## COM port parameters
 # Default COM port speed (generic)
@@ -540,7 +542,11 @@ endef
 
 .PHONY: all checkdirs spiff_update spiff_clean clean kill_term terminal gdb
 
-all: $(USER_LIBDIR)/lib$(LIBSMING).a checkdirs $(LIBMAIN_DST) $(RBOOT_BIN) $(RBOOT_ROM_0) $(RBOOT_ROM_1) $(SPIFF_BIN_OUT) $(FW_FILE_1) $(FW_FILE_2) 
+all: $(USER_LIBDIR)/lib$(LIBSMING).a checkdirs $(LIBMAIN_DST) $(RBOOT_BIN) $(RBOOT_ROM_0) $(RBOOT_ROM_1) $(SPIFF_BIN_OUT) $(FW_FILE_1) $(FW_FILE_2) $(BUILD_BASE)/$(BOOTROM_ELF)
+
+# File contains boot rom symbols required by GDB, put it somewhere easy to find
+$(BUILD_BASE)/$(BOOTROM_ELF):
+	cp $(SMING_HOME)/gdb/$(BOOTROM_ELF) $(BUILD_BASE)
 
 $(RBOOT_BIN):
 	$(MAKE) -C $(THIRD_PARTY_DIR)/rboot RBOOT_GPIO_ENABLED=$(RBOOT_GPIO_ENABLED) RBOOT_SILENT=$(RBOOT_SILENT)

Sming/gdb/gdbcmds

@@ -25,6 +25,10 @@ mem 0x60000000 0x60001fff rw
 # The target object file so GDB knows where to get symbol information
 file out/build/app_0.out
 
+# GDB needs to know about ROM functions in order to create a full stack trace
+# See https://github.com/jcmvbkbc/esp-elf-rom
+add-symbol-file out/build/bootrom.elf 0x40000000 -readnow
+
 # Change the following to your serial port and baud
 #set serial baud 115200
 #target remote /dev/ttyUSB0