How to debug STM32 startup code

[JimEli]

I’m evaluating VisualGDB. Using STM32f4 Discovery board with HAL blinky program. How does one execute a breakpoint on the startup code prior to reaching main()?

[support]

Hi,

Please simply set the breakpoint before starting debugging with F5 and VisualGDB will be able to handle this automatically.

You can also modify the behavior of the “Step into new instance” command (F10 instead of F5) to stop as soon the program is loaded into the MCU (i.e. at the reset handler) via VisualGDB Project Properties -> Embedded Debug Tweaking.

[JimEli]

Sorry, but neither of those techniques are working for me. The program is halting on first line of main. I’m using USB STLink v2.1 and BP set inside system_stm32f4xx.c/SystemCoreClockUpdate function immediately turns white when I select F5.

[support]

Thanks for the update. This looks like a different issue. If the breakpoint circle is hollow inside, the code where the breakpoint is set is not a part of the debugged binary (e.g. it is not actually called from any other code and was hence discarded).

You can double-check this by inserting the following line into the functions that don’t seem to work:

asm("bkpt 255");

It will trigger a breakpoint each time the line gets executed. If it doesn’t happen, the function is actually not called and using the “find references” command should help understand why this happens.

If the breakpoint does trigger and you see the “bkpt 255” instruction in Disassembly, but the source code doesn’t appear, the problem is due to missing/mismatching debug symbols. If this is the case, we can provide more detailed instructions on diagnosing it.

[Author]

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