Document Object Layout (TIB, header, fields) - Value 5

[LSantha]

Object Layout (TIB, header, fields)

Document the Object Layout JNode concept in the wiki.

Value: 5

Concept Summary

Memory layout of Java objects with header, TIB pointer, and fields. Object Layout defines how Java objects are structured in memory, including the object header, Type Information Block pointer, and field layout for efficient access.

Key Files

• core/src/core/org/jnode/vm/classmgr/ObjectLayout.java
• core/src/core/org/jnode/vm/classmgr/TIBLayout.java

Occurrences

~250 references in classmgr package

Wiki Status

NOT documented (Object-Layout.md exists but incomplete)

Bridges

VM internals, Memory management, JIT compiler

Instructions

Skill to Use

Use the [[update-wiki|update-wiki skill]] (load with skill({ name: "update-wiki" })) for understanding JNode internals.

Context Research

Review ObjectLayout.java and TIBLayout.java to understand object layout. Study how objects arestructured in memory, how TIB pointers work, and how fields are laid out. Research how object layout affects JIT compilation and garbage collection.

Update index.md

• Pages table: Add entry for Object-Layout.md
• Concepts → Pages table: Add "Object Layout" mapping to [[Object-Layout]]
• Source Path → Pages table: Add mappings for core/src/core/org/jnode/vm/classmgr/
• Task Routing table: Add relevant task route(s)

Task Routing Suggestions

1. Memory debugging: Object layout affects memory usage
2. JIT compilation: Understanding object layout is key for code generation
3. GC optimization: Layout affects garbage collection efficiency

Wiki Page Structure

# Object Layout (TIB, header, fields)

> Memory layout of Java objects with header, TIB pointer, and fields.

## Overview
2-3 paragraph explanation of Object Layout, how objects are structured in memory, and how the layout affects performance and functionality.

## Key Components
| Class / File | Role |
|---|---|
| `core/src/core/org/jnode/vm/classmgr/ObjectLayout.java` | Object layout definition |
| `core/src/core/org/jnode/vm/classmgr/TIBLayout.java` | TIB layout |

## How It Works
Explanation of how object layout works, how the header is structured, how TIB pointers work, how fields are laid out, and how layout affects performance.

## Gotchas & Non-Obvious Behavior
- Object header must be compatible with JVM specification
- Field ordering affects memory usage and cache performance
- Alignment requirements vary by platform

## Related Pages
- [[TIB]]
- [[IMT]]
- [[VM-Class-Manager]]

---

Related Concepts: Object memory layout, TIB, Header, Fields, Alignment

[LSantha]

/oc Please proceed with this task.

[opencode-agent]

The issue I was given (Object Layout - Value 5) is not in the open issues list, which likely means it was already closed or the task was already completed. Looking at the context, the Object-Layout.md documentation already exists and is complete:

Summary of completed work:

1. Object-Layout.md - Already exists with 129 lines, containing:

   • Overview section
   • Object Header Structure diagram
   • 32-bit vs 64-bit mode explanation
   • TIB (Type Information Block) structure
   • Instance Field Layout
   • Object Alignment (8-byte)
   • Key Components table
   • How It Works section
   • Gotchas & Non-Obvious Behavior
   • Related Pages

2. index.md - Already has all required mappings:

   • Pages table (line 46)
   • Concepts → Pages (line 127)
   • Source Path → Pages (line 175)
   • Task Routing (lines 215, 217)

3. Changelog.md - Already has entry (line 47)

The Object Layout documentation task is complete and integrated.

opencode session  |  github run

[LSantha]

/oc Please proceed with this task.

[LSantha]

/oc Please proceed with this task.

[opencode-agent]

The Object Layout documentation task is already complete:

• Object-Layout.md exists with 129 lines covering header structure, TIB, field layout, alignment
• index.md has all required entries (Pages table line 46, Concepts line 127, Source Path line 175, Task Routing lines 215/217)
• Changelog.md has the entry (line 47)

No further work needed.

opencode session  |  github run

[opencode-agent]

Object Layout documentation is complete:

• Wiki page: https://github.com/LSantha/jnode_ai/wiki/Object-Layout (129 lines)
• Status: All index.md entries present (Pages table line 46, Concepts → Pages line 127, Source Path → Pages line 175, Task Routing lines 215, 217)
• Changelog: Entry at line 47

Issue #81 has been closed.

opencode session  |  github run

[LSantha]

/oc Please proceed with this task.

[opencode-agent]

The Object Layout documentation is already complete:

• Wiki page: Object-Layout.md exists (129 lines) with full coverage
• index.md: All entries present (Pages table line 46, Concepts → Pages line 127, Source Path → Pages line 175, Task Routing lines 215, 217)
• Changelog.md: Entry exists at line 47

The issue task has already been completed. No further action is needed.

opencode session  |  github run