Case 04: No Change¶

Field	Value
Verdict	✅ NO_CHANGE
Category	No Change
Platforms	Linux, macOS, Windows
Flags	—
Detected `ChangeKind`s	—
Source files	`examples/case04_no_change/`

Category: Symbol API | Verdict: ✅ NO_CHANGE

Verdict and consumer impact¶

Nothing breaks. v2 is built from the same source as v1, so the resulting .so has a bit-for-bit equivalent ABI surface. This case is the baseline sanity check: it confirms the toolchain and comparison pipeline agree that "no change" really means no change, with zero false positives.

Old/new diff¶

v1.c	v2.c
`int stable_api(int x) { return x; }`	`int stable_api(int x) { return x; }` (identical)

abicheck command¶

gcc -shared -fPIC -g v1.c -o libfoo_v1.so
gcc -shared -fPIC -g v1.c -o libfoo_v2.so   # same source, rebuilt
abicheck compare libfoo_v1.so libfoo_v2.so

Expected abicheck finding¶

Verdict: NO_CHANGE (exit 0)

_No ABI changes detected._

Minimum evidence¶

min_evidence: L0 — the exported-symbol table alone is enough to confirm equivalence: stable_api is present with the same signature-relevant metadata in both .dynsym tables. No debug info or headers are required to reach this verdict.

Why abicheck catches it¶

abicheck diffs the two snapshots' exported-symbol sets, and (when DWARF is present, as here) their type/layout facts. With identical source and build flags, every comparable field matches, so no detector fires and the overall verdict collapses to NO_CHANGE.

Runtime failure demonstration¶

No observable effect on existing binaries — this is the compatible case. Swapping the rebuilt .so in for the original produces identical output, which is the expected outcome for a byte-identical rebuild:

gcc -shared -fPIC -g v1.c -o libfoo.so
gcc -g app.c -L. -lfoo -Wl,-rpath,. -o app
./app
# → stable_api(42) = 42

gcc -shared -fPIC -g v1.c -o libfoo.so   # rebuild from same source
./app
# → stable_api(42) = 42   (unchanged)

Safe redesign¶

N/A — this is the ideal state for a patch release. Use it as a CI sanity check: any non-zero exit from abicheck compare on an unmodified source tree signals a build reproducibility problem, not an ABI change.

Real-world example: CI pipelines that run abicheck compare on every PR use a same-source rebuild like this one as a control case — if it ever reports a change, the build (not the ABI) is the thing to investigate.

Cross-tool comparison¶

abidw --out-file v1.xml libfoo_v1.so
abidw --out-file v2.xml libfoo_v2.so
abidiff v1.xml v2.xml
echo "exit: $?"   # → 0

References¶

libabigail abidiff manual

Source files¶

CMakeLists.txt
app.c
v1.c
v1.h
v2.c
v2.h