Fix labelling for local calls

[Alan-Jowett]

This pull request includes several updates to the libfuzzer harness to enhance the functionality and remove outdated checks. The most important changes involve adding new fields to the ubpf_context_t structure, removing conditional compilation checks, and updating function signatures to include the program code.

Enhancements to ubpf_context_t structure:

• Added program_start and program_end fields to the ubpf_context_t structure to track the program boundaries. (libfuzzer/libfuzz_harness.cc)

Removal of outdated checks and conditional compilation:

• Removed the HAVE_EBPF_VERIFIER_CHECK_CONSTRAINTS_AT_LABEL conditional compilation checks and related code, simplifying the handling of store_pre_invariants option. (libfuzzer/libfuzz_harness.cc) [1] [2] [3]

Function signature updates:

• Updated the ubpf_context_from function to accept program_code as a parameter and initialize the new fields in ubpf_context_t. (libfuzzer/libfuzz_harness.cc) [1] [2]
• Modified call_ubpf_interpreter and call_ubpf_jit functions to pass program_code to ubpf_context_from. (libfuzzer/libfuzz_harness.cc) [1] [2]

Additional changes:

• Added a global vector g_pc_stack to track the program counter stack for local calls and exits. (libfuzzer/libfuzz_harness.cc)

[coveralls]

coverage: 79.201%. remained the same
when pulling c4637f1 on Alan-Jowett:fix_local_call_label
into 80cc295 on iovisor:main.