.defmt section found, but no version symbol

[scalpel4k]

Hi, I've probably read every doc about setting up defmt, but nothing seems to work.

E.g., in a link.x file I define PROVIDE(_defmt_version_ = 4);

but I still get the error when running prope-rs:

Running `probe-rs run --chip=esp32c3 --preverify --always-print-stacktrace --no-location --catch-hardfault target/riscv32imc-unknown-none-elf/release/relay`
Error: Some uncategorized error occurred.

Caused by:
    0: Failed to parse defmt data
    1: `.defmt` section found, but no version symbol - check your linker configuration

Any idea what is going wrong?

[jonathanpallant]

The symbol is called _defmt_version = 4, rather than being a symbol called _defmt_version with an address of 4.

[scalpel4k]

Thanks for the answer, but I found the code that was raising the error message, and it searches for _defmt_version_. And the elf is also containing that symbol.

The problem is when the binary gets stripped, the symbol vanishes. I wonder how all this is supposed to work in a release build .....

[jonathanpallant]

We do many many release builds with defmt, and it works perfectly. The symbol name is exactly as I described, as you can see in the source code here:

#[export_name = "_defmt_version_ = 4"]
static DEFMT_VERSION: u8 = 0;

And in the documentation I wrote here:

https://defmt.ferrous-systems.com/defmt-versions?highlight=version#defmt-versions

Symbol name: _defmt_version_ = 4

[scalpel4k]

the devil's in the details ;-) ... the underscore at the end ...

anyways. when I do a release build symbols get stripped and your static DEFMT_VERSION: u8 = 0; doesn't seem to help keeping it. I guess I might have configured the stripping somewhere in my global cargo config. Does that make sense?

[jonathanpallant]

The symbol name is exactly as I described

the underscore at the end ...

Oops 🙃 Almost exactly as I described.

In general, stripping doesn't work with defmt because the tools rely on a bunch things being in the ELF file that aren't referred to by the code in the ELF file - the stuff that strip is designed to strip.

[scalpel4k]

A hint in the docs would have saved me quite some time ;-). Do you think you can arrange that?

[jonathanpallant]

If you open a ticket, I'll look at it when I get time.