bytedeco/javacpp

Virtualizing a class causes a method returning a String return a dangling pointer

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#656 opened on Feb 25, 2023

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Description

The JNI code for method name of Module in Pytorch contains:

signed char* rptr;
StringAdapter< char > radapter(ptr->name());
rptr = radapter;

If we add an Info virtualize() on Module, the code becomes:

const signed char* rptr;
StringAdapter< char > radapter((dynamic_cast<JavaCPP_torch_0003a_0003ann_0003a_0003aModule*>(ptr) != NULL ? ((JavaCPP_torch_0003a_0003ann_0003a_0003aModule*)ptr)->name() : ptr->name()));
rptr = radapter;

The const modifier of rptr, when present or not, changes which overload of the implicit cast on the last line is applied. When absent, a copy of the string is performed. When present, no copy is performed and the returned pointer is dangling because the string it points to is freed at the end of the block.

Probably related to #374

Contributor guide

Research direction
Inspect the generated JNI code to understand how the const qualifier affects the string copying logic. Check the related issue #374 for additional context.
Tech stack
javacpp
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JavaJNI
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30