Make builds of esp_app_desc reproducible

[irriden]

Zero out time and date fields of esp_app_desc_t when esp_idf_app_compile_time_date is not set

[irriden]

This is relevant when CONFIG_APP_REPRODUCIBLE_BUILD=y in sdkconfig

[Vollbrecht]

Ty for your PR, in the end we found the culprits and got it working ;) PR LGTM!

[irriden]

@Vollbrecht sorry for the force pushes here, I think this is now correct.

[irriden]

@Vollbrecht I believe 3f0c137 is better. Now my question is why CONFIG_APP_COMPILE_TIME_DATE is set when CONFIG_APP_REPRODUCIBLE_BUILD is set:

https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/kconfig.html#config-app-compile-time-date

[Vollbrecht]

do you mean because it says so in the documentation, or is it the real behavior? Could be that the docu is wrong here. You can check what flags are set and not with cargo rustc -- --print cfg

[irriden]

do you mean because it says so in the documentation, or is it the real behavior? Could be that the docu is wrong here. You can check what flags are set and not with cargo rustc -- --print cfg

Thanks for the tip! This is the real behavior.

When I remove the CONFIG_APP_REPRODUCIBLE_BUILD from sdkconfig, CONFIG_APP_COMPILE_TIME_DATE is set.

When I set CONFIG_APP_REPRODUCIBLE_BUILD=y, CONFIG_APP_COMPILE_TIME_DATE is set.

If I want a reproducible build, I have to do:

CONFIG_APP_REPRODUCIBLE_BUILD=y
CONFIG_APP_COMPILE_TIME_DATE=n

[Vollbrecht]

hmm that sounds interesting, for me logically i would assume that CONFIG_APP_REPRODUCIBLE_BUILD will unset CONFIG_APP_COMPILE_TIME_DATE. Maybe its a bug in esp-idf?

Well for our case i would see it more ergonomic to just use the CONFIG_APP_REPRODUCIBLE_BUILD as the base flag to erase the timing data from the app_desc, if the user choose to use our macro for it. Though i have no strong opinion on it.

[irriden]

@Vollbrecht I am happy to leave that decision to the maintainers here - just let me know which solution you would merge.

[Vollbrecht]

i think i would go with CONFIG_APP_REPRODUCIBLE_BUILD last word and the one who will merge is @ivmarkov

[ivmarkov]

• CONFIG_APP_REPRODUCIBLE_BUILD appeared since ESP IDF 5.0. It is not present in ESP IDF 4.X
• CONFIG_APP_COMPILE_TIME_DATE was always there. In ESP IDF 5, if you set CONFIG_APP_REPRODUCIBLE_BUILD, it will unset - in the ESP IDF code though, not in kconfig CONFIG_APP_COMPILE_TIME_DATE

Based on the above we should do exactly what ESP IDF 5 does, here, i.e., only set the date and time when

#[cfg(all(esp_idf_app_compile_time_date, not(esp_idf_app_reproducible_build)))]

... and otherwise keep them zeroed.

[irriden]

Done. Thanks for your time.

[Vollbrecht]

don't forget to run cargo fmt and cargo clippy maybe it wants you to use De Morgan's laws 😸

[irriden]

It seems to me both of them are happy with f4d1296 ?

[kpcyrd]

Adding onto this, I found that adding CONFIG_APP_EXCLUDE_PROJECT_VER_VAR=y also helps because otherwise the output of git describe --always --tags --dirty gets embedded into your firmware (which you may not want).