Diagnosing Bus Fault

Question

I'm relatively new to hardware development and debugging. 
 I'm getting a bus fault at random points during hardware execution. 
 I'm trying to use `arm-none-eabi-addr2line` to figure out where the offending instruction is, but I'm getting strange results. Often, the Faulting instruction address reported by the device has no symbol on it - I get "??:?" when I try to look it up. Sometimes, the reported offending line is a close-bracket (a "}"). Any help on this? I'm currently using 
 VSCode with NRFConnect 2.3 Zephyr 3.3 Windows 10 I'm connecting the my board with a DK acting as the JLink. 
 Best, S.

Raoul · Accepted Answer

Hi again, sorry to let you wait! 
 I'm relatively new to hardware development and debugging. 
 No problem, it's great that you're looking into these kind of debugging tools. I should be using addr2line more myself. 
 Anyway, the addr2line man page states the following: 
 "If the file name or function name can not be determined, addr2line will print two question marks in their place. If the line number can not be determined, addr2line will print 0" 
 So why can't addr2line find the file or function name? Compiler optimization is by far the most likely reason for this. GCC and other optimizing compilers will try (when asked) to make code faster without affecting functionality. But this has the side effect of the executable not directly matching your source code any more. 
 This Stack Overflow page provides a good explanation: https://stackoverflow.com/questions/20816302/is-it-possible-to-use-addr2line-with-application-compiled-with-release-optimizat 
 When you build a Zephyr application without any debug options, the default config is for GCC to optimize your code for speed (with -O3 , I think). If you want to optimize for debuggability, you 
 can add this Kconfig option : 
 CONFIG_DEBUG_OPTIMIZATIONS=y 
 (There's also CONFIG_NO_OPTIMIZATIONS which some are tempted to use, but I just learned from this little comment that CONFIG_DEBUG_OPTIMIZATIONS might actually produce faster code since it tries some -O1 optimizations.) 
 Assuming you're using the VS Code extension, CONFIG_DEBUG_OPTIMIZATIONS is enabled automatically when you select the "Enable debug options" option when adding a new build configuration. So I recommend just adding a build configuration for debugging: 
 
 Optimizing for debugging can make your code larger, so if you're unlucky, it might not fit in RAM/Flash anymore. But if it fits, I think addr2line should now work correctly. 
 If it doesn't fit, you could perhaps optimize only part of your application, as described here: Disable optimization of part of the code through CMAKE But I haven't tried that myself yet. 
 Let me know if that works! 
 Best regards, 
 Raoul

Diagnosing Bus Fault

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