add executable flag to linker

[katsyoshi]

No description provided.

[chatgpt-codex-connector]

💡 Codex Review

caotral/lib/caotral/linker/builder.rb

Lines 110 to 114 in e52274c

	main_sym = symtab_section.body.find { |sym| sym.name_string == "main" }
	raise Caotral::Binary::ELF::Error, "main function not found" if executable && main_sym.nil?
	main_offset = main_sym.nil? ? 0 : main_sym.value + start_len
	start_bytes[1, 4] = num2bytes((main_offset - 5), 4)
	text_section.body.prepend(start_bytes.pack("C*"))

Skip _start stub when executable is false

With the new executable: false option, main_sym can be nil, but the builder still patches and prepends the _start stub. When main_sym is nil, main_offset becomes 0 and start_bytes gets a rel32 of -5, producing a call-to-self stub that is meaningless for non-executable output and shifts all .text symbols. This means linking a shared library or non-executable with linker: "self", executable: false will still embed an invalid entry stub rather than leaving the code intact, which is likely unintended and can corrupt the resulting artifact. Consider skipping the stub and symbol offset adjustment entirely when executable is false.

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