Add "bbconfig" applet to config

[ryanwoodsmall]

BusyBox supports a sort of reflective applet called "bbconfig" which will dump the .config used while building the binary. This can be enabled with these config options:

CONFIG_BBCONFIG=y
CONFIG_FEATURE_COMPRESS_BBCONFIG=y

This is a nicety but it's pretty useful when attempting to debug an issue with a container, the binary itself, etc.

[tianon]

Interesting! I did some size comparisons, and here's my results:

• before: busybox:uclibc image ~1.16MB, tarball ~616KB
• adding CONFIG_BBCONFIG: image ~1.22MB, tarball ~624KB
• adding both config options: image ~1.2MB, tarball ~624KB

Any idea why this isn't enabled by default in defconfig? Do you know whether upstream BusyBox maintainers officially recommend either including it or not including it? (I can't seem to find a lot of good info about it other than it exists. :sweat_smile:)

[ryanwoodsmall]

Upstream is pretty conservative about time/space tradeoffs. Best (only?) documentation is the source, but it doesn't have a ton of reasoning on defaults: https://git.busybox.net/busybox/tree/miscutils/bbconfig.c

[tianon]

In thinking about this more, I'm inclined to think this isn't really worth the additional size (even if it's small), since the things we enable above make defconfig are already quite minimal:

https://github.com/docker-library/busybox/blob/f7661b44becfe763eb1fcb8c176d44f80c742e00/uclibc/Dockerfile.builder#L184-L194

[ryanwoodsmall]

Agreed. Closing. Thanks all!