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faqs.md

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FAQs

Are there restrictions on what GPRs I can use in my diags?

Yes. The Thread Pointer (x4) and Global Pointer (x3) registers are reserved for JumpStart purposes and should not be used in diags. TP is used to point to a per cpu attributes structure and GP is used as a temporary in JumpStart routines.

Diags are expected to follow the RISC-V ABI Calling Convention.

I'm unable to run spike in interactive debugging mode with meson test.

Running spike through meson test breaks spike's command line debugging facility (-d) for interactive debugging.

You will need to run spike manually with -d for interactive debugging.

What's the best way to debug a diag that is behaving incorrectly?

  • If your diag can run on Spike, generate the spike trace and see where things go off the rails.
    • Look for trap to find unexpected exceptions.
    • Look for the point where your code returns to the JumpStart code.
    • Run spike with the -d flag to step through your diag and inspect registers and memory.
  • Build with the --buildtype debug to turn off optimizations and generate debug information. The disassembly generated will have your code interleaved with the assembly, making it easier to correlate the two.