Help with crt0 SIGTRAP error? about arduino-pico

[maxgerhardt]

When you upload a blinky firmware in the current configuration (and not start debugging), does that run?

[rivimey]

I thought about that, and to verify I can upload and run something correctly I compiled a blinky in Rust (because doing so uses only a rust compiler toolchain). This worked fine, no problems.

Is that what you meant?

[maxgerhardt]

Not really, I meant a blinky written with this regular Arduino-Pico core. It should be flashable via the cmsis-dap protocol, setup as you now have.

#include <Arduino.h>
#define LED LED_BUILTIN // or whatever
void setup() { pinMode(LED, OUTPUT); }
void loop() { digitalWrite(LED, digitalRead(LED) ^ 1); delay(1000); }

[rivimey]

Aside: before I used platformio, I compiled my project using a simple Makefile with compiler flags cribbed from an Arduino build; this built and linked ok but also failed in the crt0 code in what seems to be a very similar way. The switch to platformio was supposed to avoid the 'handcrafted' aspect of this build. Sadly this doesn't seem to have worked.

I will say I'm not doing anything at all weird, especially in during crt0/start/main startup. There are some c++ constructors which could perhaps start doing something but as far as I know that happens after crt0, not during.

[earlephilhower]

Without a full MCVE we're really just guessing here and not likely to get down to the root cause, but...

I will say I'm not doing anything at all weird, especially in during crt0/start/main startup. There are some c++ constructors which could perhaps start doing something but as far as I know that happens after crt0, not during.

C++ constructors are all called as part of the C++ runtime initialization, in random order. If a C++ global object constructor uses another global object there is no guarantee that the called object's constructor will have been called. Recipe for confusion, at least, or a crash, more likely.

That said, please run @maxgerhardt 's very basic blink example and verify that works. If it does, there's a problem in the crashing app's code. If blink doesn't work, there's a toolchain config problem (wrong flash type specified, maybe?)...

[rivimey]

Thanks both for your suggestions, appreciated. I first tried the blinky code (by replacing src/* with a cpp file containing that code) and it worked fine.

I then tried reinstating all my project's code (except u8g2 and the display thread on core 1) but commenting out any line that could cause code execution, so both of the global c++ objects (one for each core) and so on. I then included the lines from blinky so it would run that within the context of my code. That worked too.

I then re-enabled one core's global constructor, and it failed immediately, as (now) expected. It seems the point about constructor initialisation is well made, though I'm unsure if this is about ordering or not, as there is only one global constructor being enabled here.

I then made the global object a pointer, with an initialisation within arduino setup(). That also worked (in so far as it didn't crash -- there was still no loop() code and all the non-trivial setup code was commented out too).

I then thought I would single-step through the setup() code, see what was happening. So, in debug mode, set a breakpoint in setup() and upload. It stopped at the beginning of the framework's main.cpp as expected. I click on 'step' once and it dies with "trap 6". I can't see anything else wrong in the log, and a breakpoint set a couple of lines later in main() [on the freeRTOS check line] is not hit.

A thought: Could this trap be something to do with debug compile or link settings?

Fatal signal: 
Abort trap: 6

----- Backtrace -----
Backtrace unavailable
---------------------
A fatal error internal to GDB has been detected, further
debugging is not possible.  GDB will now terminate.

Out of all this I am somewhat confused why bad/faulty app code can cause a crash in crt0 code -- is this just about c++ initialisation doing unexpected things or is something else going on?