zig c++ adds ubsan in release builds

[FedeDP]

Zig Version

0.14.0

Steps to Reproduce and Observed Behavior

Previously, we were using 0.14.0-dev.3188+34644511b and everything was fine.
After bumping to 0.14.0 i am facing an issue while configuring protobuf to use zlib, related to ubsan, that seems to get enabled by default even if the build is -O{2,3}:

| namespace conftest {
|   extern "C" int zlibVersion ();
| }
| int
| main (void)
| {
| return conftest::zlibVersion ();
|   ;
|   return 0;
| }
configure:20813: zig-cxx -o conftest -O2 -std=c++11 -DNDEBUG -I/home/federico/Work/libs/build_zig/zlib-prefix/src/zlib  -L/home/federico/Work/libs/build_zig/zlib-prefix/src/zlib  conftest.cpp -lz   >&5
ld.lld: error: undefined symbol: __ubsan_handle_shift_out_of_bounds
>>> referenced by zutil.c:44
>>>               zutil.o:(zlibCompileFlags) in archive /home/federico/Work/libs/build_zig/zlib-prefix/src/zlib/libz.a
>>> referenced by zutil.c:50
>>>               zutil.o:(zlibCompileFlags) in archive /home/federico/Work/libs/build_zig/zlib-prefix/src/zlib/libz.a
>>> referenced by zutil.c:56
>>>               zutil.o:(zlibCompileFlags) in archive /home/federico/Work/libs/build_zig/zlib-prefix/src/zlib/libz.a

ld.lld: error: undefined symbol: __ubsan_handle_sub_overflow
>>> referenced by zutil.c:132
>>>               zutil.o:(zError) in archive /home/federico/Work/libs/build_zig/zlib-prefix/src/zlib/libz.a

ld.lld: error: undefined symbol: __ubsan_handle_out_of_bounds
>>> referenced by zutil.c:132
>>>               zutil.o:(zError) in archive /home/federico/Work/libs/build_zig/zlib-prefix/src/zlib/libz.a

ld.lld: error: undefined symbol: __ubsan_handle_pointer_overflow
>>> referenced by zutil.c:132
>>>               zutil.o:(zError) in archive /home/federico/Work/libs/build_zig/zlib-prefix/src/zlib/libz.a

ld.lld: error: undefined symbol: __ubsan_handle_type_mismatch_v1
>>> referenced by zutil.c:132
>>>               zutil.o:(zError) in archive /home/federico/Work/libs/build_zig/zlib-prefix/src/zlib/libz.a
configure:20813: $? = 1

Note: zig-cxx is a small wrapper:

#!/bin/bash

exec zig c++ -target $(uname -m)-linux-gnu.2.17 "$@"

What i get is: zlibVersion has some kind of ubsan. But since i am building protobuf in -O3 i did not expect ubsan to be enabled on the build.

A workaround i found is to use -O5; at that point probably some conditional somewhere disables ubsan, then the build works fine and clang fallbacks at -O3:

warning: optimization level '-O5' is not supported; using '-O3' instead

Given this all worked fine until a few weeks ago, i think #22488 perhaps changed anything?

Expected Behavior

The release optimized build should not enforce ubsan.

[alexrp]

cc @Rexicon226

[alexrp]

This really needs more complete reproduction steps.

[FedeDP]

Uh i found the issue; it was related to the fact that zlib was not built with -O3. Sorry for the noise!

[Rexicon226]

This is a known and unfortunate regression from the old ubsan behavior tracked here #23052. We'll detect whether the input objects were built with ubsan enabled, and go off of that in the future for better defaults. As you said, it shouldn't be pulling in ubsan if the inputs don't use it.

[FedeDP]

Thanks @Rexicon226 i am going to subscribe to the issue.