Global variable support

[Alan-Jowett]

Description

This pull request introduces several changes to the eBPF codebase, primarily focusing on adding support for global variable sections and resolving map value addresses. The changes span multiple files and include new functions, updates to existing structures, and modifications to metadata tables.

Enhancements to Global Variable Support:

• include/bpf2c.h: Added global_variable_section_t struct and a function pointer for retrieving global variable sections in metadata_table_t. [1] [2]
• tests/bpf2c_tests/expected/*: Updated metadata tables in multiple test files to include the new global variable sections function. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

Map Value Address Resolution:

• libs/execution_context/ebpf_core.c: Added ebpf_core_resolve_map_value_address function to resolve map handles to addresses of the first value in the map.
• libs/execution_context/ebpf_core.h: Declared the new ebpf_core_resolve_map_value_address function.
• libs/execution_context/ebpf_maps.c: Added ebpf_map_get_value_address function to get the address of the first value in an array map.
• libs/execution_context/ebpf_maps.h: Declared the new ebpf_map_get_value_address function.

Native Provider Enhancements:

• libs/execution_context/ebpf_native.c: Added fallback function for global variable sections and updated the provider attach callback to set this fallback if not provided. Implemented _ebpf_native_resolve_map_value_addresses to handle the resolution of map value addresses and setup global variables during program load. (F3dca3c6L37R37, [1] [2] [3] [4]

Miscellaneous:

• libs/api/ebpf_api.cpp: Added a comment regarding a fragile heuristic related to map_entry_t.
• tests/bpf2c_tests/expected/*: Updated the version of NPI_CLIENT_CHARACTERISTICS to 1 and added a check for the provider registration instance version in multiple test files. [1] [2] [3] [4]

Testing

CI/CD

Documentation

No.

Installation

No.

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