Skip empty symbol names while attempting to parse json

[MathiasKoch]

Avoid Error: EOF while parsing a value at line 1 column 0 if .defmt section should contain a symbol with empty name.

This might occur if you run arm-none-eabi-objcopy ${IN} ${OUT}, where IN is the output ELF of cargo build.

[japaric]

Thanks for the PR! Could you describe in more detail how to cause the error that this is fixing? Does the error come from objcopy? Or you running objcopy on a single ELF file before passing that to probe-run?

[MathiasKoch]

Ahh, yeah. After reading my description again, I can see how it might be a bit ambiguous.

If i compile a device side firmware file using defmt, and then run that ELF file through ? objcopy, the resulting ELF file looks 100% identical when looking at it with nm and objdump, but it contains "" (empty string name) symbols in the .defmt section among others. I still don't understand why this happens though?!

[japaric]

Thanks for clarifying. I'll reproduce the issue locally to get a better understanding at what objcopy is doing. (Mostly because I'm curious)

I'm OK with this PR. Could you add a comment to the source code indicating why we are skipping empty symbol names? (i.e. "they may be added by objcopy")

[MathiasKoch]

Yeah sure. If you end up figuring out why it produces these empty strings, please let me know somewhere :) eg Matrix..

In case it matters, I have seen it using

> arm-none-eabi-objcopy --version
GNU objcopy (GNU Binutils) 2.34
Copyright (C) 2020 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) any later version.
This program has absolutely no warranty.

I have spent the better part of two full days trying to find out what happened, and have split my entire firmware to pieces in the process 🕵️

[japaric]

Thanks!