Can you step through code with GDB over UART? ("No symbol table")

[hamishcunningham]

hi folks!

Am I right in thinking that when debugging with GDB over the serial line it isn't possible to step through code?
Or am I missing some compiler flag?

I can get a backtrace, but when I try "info locals" or "step" it complains about missing info...

Output below; I'm running ESP IDF f586f5e from Ubuntu 12.04 with a C++ build that includes
the flags "-Og -ggdb"...

I've watched Neil Kolban's video https://www.youtube.com/watch?v=p63VEYS7ZUw (Thanks Neil!)
and only difference I see with his output is that my backtrace starts with an undefined location:
#0 0x400014fd in ?? ()
whereas I think his has a decoded address... Perhaps I'm missing something?

Code attached.

Thanks!
Hamish


[D][main.cpp:16] minapp_setup(): minapp setup
Guru Meditation Error: Core 1 panic'ed (LoadProhibited)
. Exception was unhandled.
Core 1 register dump:
PC : 0x400014fd PS : 0x00060330 A0 : 0x800daa4c A1 : 0x3ffb86e0
A2 : 0x00000000 A3 : 0xfffffffc A4 : 0x000000ff A5 : 0x0000ff00
A6 : 0x00ff0000 A7 : 0xff000000 A8 : 0x00000000 A9 : 0x3ffb86a0
A10 : 0x00000000 A11 : 0xffffffff A12 : 0x00000004 A13 : 0x00000001
A14 : 0x3ffb8820 A15 : 0x00000003 SAR : 0x00000004 EXCCAUSE: 0x0000001c
EXCVADDR: 0x00000000 LBEG : 0x400014fd LEND : 0x4000150d LCOUNT : 0xffffffff

Backtrace: 0x400014fd:0x3ffb86e0 0x400daa49:0x3ffb86f0 0x400d2d55:0x3ffb8a00 0x400d2785:0x3ffb8a50 0x400d27ab:0x3ffb8a70
0x400daa49: _vfprintf_r at /Users/ivan/e/newlib_xtensa-2.2.0-bin/newlib_xtensa-2.2.0/xtensa-esp32-elf/newlib/libc/stdio/../../../.././newlib/libc/stdio/vfprintf.c:1529

0x400d2d55: printf at /Users/ivan/e/newlib_xtensa-2.2.0-bin/newlib_xtensa-2.2.0/xtensa-esp32-elf/newlib/libc/stdio/../../../.././newlib/libc/stdio/printf.c:58

0x400d2785: minapp_setup() at /home/hamish/unfishy/minapp/main/./main.cpp:20

0x400d27ab: minapp_task(void*) at /home/hamish/unfishy/minapp/main/./main.cpp:29


Entering gdb stub now.
$T0b#e6GNU gdb (crosstool-NG crosstool-ng-1.22.0-80-g6c4433a) 7.10
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Reading symbols from /home/hamish/unfishy/minapp/build/minapp.elf...done.
Remote debugging using /dev/ttyUSB0
0x400014fd in ?? ()
(gdb) bt
#0 0x400014fd in ?? ()
#1 0x400daa4c in _vfprintf_r (data=<optimized out>, fp=<optimized out>, fmt0=<optimized out>, ap=...) at ../../../.././newlib/libc/stdio/vfprintf.c:1529
#2 0x400d2d58 in printf (fmt=0x3f402da8 "%s") at ../../../.././newlib/libc/stdio/printf.c:58
#3 0x400d2788 in minapp_setup () at /home/hamish/unfishy/minapp/main/./main.cpp:20
#4 0x400d27ae in minapp_task (pvParameter=0x0) at /home/hamish/unfishy/minapp/main/./main.cpp:29
(gdb) info locals
No symbol table info available.
(gdb) step
Cannot find bounds of current function
(gdb)

[kolban]

Howdy Hamish,
This is about the best docs on GDB stub I have seen:

http://esp-idf.readthedocs.io/en/latest ... or-gdbstub

As that doc says, you can read memory and variables, look at stack frames and otherwise interrogate the memory state of a crashed application. But ... that's it. If you need to step through your executing code then my belief is that the JTAG functions are what you will want to investigate.

[hamishcunningham]

Thanks Neil!