Fix spurious close(fd<3) errors for stripped ELFs

[jserv]

Stripped ELFs lack symbol tables, so the 'exit' symbol cannot be found and exit_addr remains uninitialized. This caused on_exit to never become true, resulting in spurious error messages when crt0 calls close(0,1,2) during program termination.

Changes:

• Add exit_addr check in syscall_close to allow close(fd<3) when no exit symbol was found (stripped ELF case)
• Explicitly initialize exit_addr to 0 before symbol lookup
• Also check for '_exit' symbol as fallback for different toolchains

---

Summary by cubic

Fix false close(fd<3) errors when running stripped ELFs by properly handling missing exit symbols and avoiding uninitialized exit_addr use. This prevents noisy logs when crt0 closes stdin/stdout/stderr on exit.

• Bug Fixes
  • Initialize exit_addr to 0 before symbol lookup.
  • Resolve exit address by checking "exit" and falling back to "_exit".
  • In syscall_close, only flag fd<3 closes as errors if on_exit is false and exit_addr is set; otherwise allow them silently for stripped ELFs.

^{Written for commit 674f9d9. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

[jserv]

Benchmarks

Details

Benchmark suite	Current: 674f9d9	Previous: b26939d	Ratio
Dhrystone	1626 DMIPS	1597.333 DMIPS	0.98
CoreMark	971.664 iterations/sec	973.382 iterations/sec	1.00

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