doc: abi overview

[junrushao]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @junrushao, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the project's documentation by introducing a detailed and structured overview of the TVM-FFI Application Binary Interface. The new documentation clarifies the fundamental design principles, data structures, and interaction patterns of the ABI, supported by concrete C code examples. This addition aims to provide developers with a clearer understanding of how to work with TVM-FFI at a low level, improving the accessibility and maintainability of the system.

Highlights

• New ABI Overview Documentation: A new reStructuredText document (docs/concepts/abi_overview.rst) has been added, providing a comprehensive overview of the TVM-FFI ABI. This document details core principles, data types like Any, Object, Tensor, Function, Exception, Module, and String/Byte types, and their usage patterns.
• Accompanying C Code Examples: A new C example file (examples/abi_overview/example_code.c) has been introduced to provide practical, low-level demonstrations for the ABI concepts explained in the new documentation.
• Documentation Structure Refinement: The existing docs/index.rst has been updated to include the new ABI overview, and docs/concepts/any.rst and docs/concepts/object_and_class.rst have been modified to add internal cross-reference labels, improving navigability and consistency.
• Migration of Legacy ABI Doc: The previous Markdown-based ABI overview (docs/concepts/abi_overview.md) has been renamed to docs/concepts/abi_overview_legacy.rst, indicating a shift towards reStructuredText for core documentation.
• C API Header Annotations: The include/tvm/ffi/c_api.h file now includes // [TAG.begin] and // [TAG.end] comments around key ABI structure and enum definitions, facilitating automatic inclusion of code snippets in the new documentation.

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[gemini-code-assist]

Summary of Changes

Hello @junrushao, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the TVM-FFI documentation by introducing a new, comprehensive overview of its Application Binary Interface (ABI). The new document, written in reStructuredText and supported by concrete C code examples, aims to clarify the fundamental principles, data structures, and interaction patterns of the FFI system. This change improves the accessibility and understanding of TVM-FFI's low-level mechanisms for developers, ensuring a more robust and maintainable codebase.

Highlights

• New ABI Overview Documentation: A comprehensive reStructuredText document, docs/concepts/abi_overview.rst, has been added. This document provides a detailed overview of the TVM-FFI Application Binary Interface (ABI), covering its core principles, data types (Any, Object, Tensor, Function, Exception, Module, String, and Byte), and usage patterns with low-level C code examples.
• Accompanying C Code Examples: A new C example file, examples/abi_overview/example_code.c, has been introduced. This file contains practical code snippets that are directly referenced within the abi_overview.rst document, illustrating how to interact with the TVM-FFI ABI concepts in C.
• Documentation Structure and Cross-Referencing Improvements: The main documentation index (docs/index.rst) has been updated to include the new ABI overview. Additionally, existing documentation files (docs/concepts/any.rst, docs/concepts/object_and_class.rst) have been modified to add specific cross-reference targets, enhancing navigation and linking within the documentation set.
• C API Header Annotations: The include/tvm/ffi/c_api.h file has been augmented with // [TAG.begin] and // [TAG.end] markers around key C ABI struct and enum definitions. These annotations are crucial for documentation generation tools, allowing specific code sections to be directly embedded and referenced in the new ABI overview.
• Legacy Document Handling: The previous ABI overview document, docs/concepts/abi_overview.md, has been renamed to docs/concepts/abi_overview_legacy.rst. This indicates a transition to a new, more detailed, and structured ABI documentation approach.

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Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
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[gemini-code-assist]

Code Review

This pull request introduces comprehensive documentation for the TVM-FFI ABI, complete with low-level C code examples. The changes are well-organized, adding a new overview page, example code, and updating existing documentation and header files to support the new content. My review has identified a critical bug in an example C function and a few minor areas for improvement in the documentation for clarity and completeness.

[gemini-code-assist]

Code Review

This pull request introduces a comprehensive ABI overview document, which is a great addition. I've found a few areas in the new documentation that could be improved for clarity and correctness, including a grammatical error, a 'TBA' placeholder, and a minor wording issue. More importantly, I've identified a bug in one of the C code examples where a function incorrectly handles type casting, which could lead to incorrect behavior. My review includes suggestions to fix these issues.

[junrushao]

/gemini review

[gemini-code-assist]

Code Review

This pull request is a significant and valuable documentation refactoring. It introduces a new, comprehensive document, abi_overview.rst, to serve as a central reference for the TVM FFI C ABI. Consequently, other related documents have been streamlined by removing duplicated C-level details and adding links to this new central page. This change greatly improves the structure and maintainability of the documentation. The new document is well-written and effectively uses literalinclude to embed code snippets from a dedicated example file, which is an excellent practice. My review includes a couple of suggestions to further enhance the clarity of the new abi_overview.rst document. Overall, this is a high-quality contribution.

[junrushao]

/gemini Review

[gemini-code-assist]

Code Review

This pull request is a significant and valuable documentation refactoring. It centralizes the TVM FFI ABI low-level details into a new abi_overview.rst document, which improves maintainability and clarity. The old markdown version is removed, and other documentation files are updated to link to the new central document, removing duplicated content. A new C file with code examples is also added to support the new documentation.

The changes are well-executed. I have a couple of suggestions to improve the new code examples in abi_overview.rst by adding explicit notes about resource management. This will help prevent potential resource leaks for users who copy-paste the examples.

[tqchen]

some followup notes

[tqchen]

need note

Before calling the function, caller must set `result->type_index` to be kTVMFFINone, or any type index that do not corresponds to an on-heap object.

[junrushao]

It's covered in another doc: https://tvm.apache.org/ffi/concepts/func_module.html#tvm-ffi-c-abi. but happy to emphasize it