Case 113: ABI-tag set change ([abi:cxx11] lost on a single symbol)¶

Field	Value
Verdict	🔴 BREAKING
Category	Breaking
Platforms	Linux
Flags	ABI break
Detected `ChangeKind`s	`abi_tag_changed`
Source files	`examples/case113_abi_tag_changed/`

Category: Binary ABI break / C++ mangling | Verdict: 🔴 BREAKING

What changed¶

In v1, get_id() carries an explicit Itanium ABI tag via [[gnu::abi_tag("cxx11")]], so its mangled symbol is _Z6get_idB5cxx11v (the B5cxx11 component encodes the tag). In v2 the tag is removed, so the symbol becomes _Z6get_idv. The demangled declaration is identical, but the two mangled names are different symbols.

Unlike the libstdc++ dual-ABI mass flip (which churns hundreds of symbols at once and is reported once as glibcxx_dual_abi_flip_detected), this is a single symbol whose ABI-tag set changed.

How abicheck catches it¶

abi_tag_changed fires because the function's ABI-tag set differs while the base (tag-stripped) mangled name matches. A consumer linked against the v1 tagged symbol gets an undefined-symbol error at load time against v2. The detector stays silent when a mass dual-ABI flip is detected, to avoid duplicate noise.

Files¶

v1.cpp / v2.cpp — the two library builds, with the tagged vs untagged get_id() declaration inlined (no header: the snapshot is taken from the compiled library's DWARF). This case is Linux-only — the ABI-tag rename is only visible via the ELF/DWARF path.
app.cpp — minimal consumer stub

Source files¶

CMakeLists.txt
app.cpp
v1.cpp
v2.cpp