Release 21.3 broke ABI, ironically because of #10271

[Vogtinator]

What version of protobuf and what language are you using?
Version: v21.2 -> v21.3
Language: n/a

What operating system (Linux, Windows, ...) and version?
openSUSE Tumbleweed

We updated protobuf from 21.2 to 21.3 (21.4 should be affected the same way) and multiple applications/libraries stopped working due to this error:

/usr/sbin/usbguard-daemon: symbol lookup error: /lib64/libusbguard.so.1: undefined symbol: _ZN6google8protobuf8internal16InternalMetadataD1Ev

It appears like as a side effect of #10271, the symbol is now completely missing, but libraries/applications build against the previous version still depend on it. This requires a SOVER bump.

CC @pitrou @fowles @coryan

[fowles]

Protobuf does not offer ABI stability. Simply put C++ is actively adversarial to it. That fix was accept to make DEBUG/NDEBUG have similar ABI when built together, but even that level of conformance is best effort only.

[Vogtinator]

Protobuf does not offer ABI stability.

That is not an issue by itself, but you must bump the sover on each relevant change.

[fowles]

Can you look in the build process for where we set the sover? The easiest answer might be to bump it for every release

[dirkmueller]

please reopen :)

[Vogtinator]

FWICT it's set here, in the slightly odd libtool version format (https://www.gnu.org/software/libtool/manual/html_node/Libtool-versioning.html#Libtool-versioning):

protobuf/src/Makefile.am

Line 21 in 53f7830

PROTOBUF_VERSION = 32:4:0

It might be appropriate to switch over to the -release style of library versioning, which could just include the version number: https://www.gnu.org/software/libtool/manual/html_node/Release-numbers.html

[jengelh]

Simply put C++ is actively adversarial to it.

Some projects change their exported symbol set at the flick of ./configure --disable-something, or change a struct's layout as a result of such switch, making any two builds of the same version on the same platform already incompatible, irrespective of the language being used for the project.