Fix try/catch control flow in eBPF and missing catch body in userspace

[SiyuanSun0736]

Description

The current implementation of the try/catch mechanism contains two logic gaps that prevent examples/error_handling_demo.ks from executing correctly:

1. eBPF Control Flow: In the eBPF backend, throw (via IRThrow) only assigned a value to the error variable but did not interrupt the execution of the try block. Subsequent instructions in the try block were still executed.
2. Userspace Code Generation: The userspace backend generated a C switch statement with a placeholder comment (/* Handle error here */) instead of recursing into the actual instructions defined within the catch block.

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Technical Breakdown

eBPF Backend (src/ebpf_c_codegen.ml)

• Context Variable: Added current_catch_label to the c_context type.

• Label Management:

• IRTry now generates a unique catch_label and stores it in the context before processing the try instructions.

• A label definition (label:) is now emitted after the try block but before the catch logic.

• Jump Logic: IRThrow now emits a goto statement targeting the catch_label, ensuring immediate exit from the try block upon an error.

Userspace Backend (src/userspace_codegen.ml)

• Recursive Generation: Replaced the static placeholder string in the catch case with a mapping of generate_c_instruction_from_ir over the catch_body list.
• String Integration: The generated instructions are now concatenated and properly indented within the C case statement.

error_handling.patch

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These changes ensure that:

• In eBPF programs, a throw effectively skips the remainder of the try block.

• In Userspace programs, the logic defined inside a catch block is actually compiled into the final C code.

[congwang-mk]

Please submit a PR