STILL: Recovering Lowered STL Semantics for LLM-assisted C++ Decompilation

Xiaohan Wang, Kevin Leach


Abstract
LLM-assisted decompilation improves readability and re-executability, but still underperforms on stripped C++ functions that use the Standard Template Library (STL). Compilation, optimization, and symbol stripping remove or obscure source-level semantics such as container types and library-call structure, while traditional decompiler output often fails to recover them. We present STILL, a structured semantic interface that predicts function-level STL container semantics from stripped control-flow graphs and renders them as compact hints for LLM refinement. On StlBench, STILL predicts common container-level STL semantics, with the strongest cross-dataset results for stable string and vector slices. On stripped HumanEval decompilation, these hints enable DeepSeek-chat refinement to reach 28.4% executability, compared with 17.4% for no-hint refinement and 8.9% for raw Ghidra decompilation; hint utility is downstream-backbone-dependent, with decompilation-specialized models requiring lightweight adaptation to benefit from the same interface.
Anthology ID:
2026.emnlp-main.1898
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
43272–43287
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1898/
DOI:
Bibkey:
Cite (ACL):
Xiaohan Wang and Kevin Leach. 2026. STILL: Recovering Lowered STL Semantics for LLM-assisted C++ Decompilation. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 43272–43287, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
STILL: Recovering Lowered STL Semantics for LLM-assisted C++ Decompilation (Wang & Leach, EMNLP 2026)
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https://aclanthology.org/2026.emnlp-main.1898.pdf