write/macho: ensure Mach-O subsections are not zero size #676
Conversation
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This is to fix rust-lang/rustc_codegen_cranelift#1456, along with the cranelift change in philipc/wasmtime@d851125 |
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Note that rustc_codegen_cranelift isn't currently setting |
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This code in llvm confirms that basing this on llvm always sets |
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For zero length functions, llvm emits a noop instead: I'm not keen on handling this here. I think that's better done in cranelift if needed. |
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@bjorn3 Are you happy with this change? |
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This PR looks fine to me. |
For Mach-O, `add_symbol_data` now ensures that the symbol size is at least 1 when subsections via symbols are enabled. This change was made to support linking with ld-prime. It is also unclear how this previously managed to work with ld64. `write::Object::add_subsection` no longer enables subsections via symbols for Mach-O. Use `set_subsections_via_symbols` instead. This change was made because Mach-O subsections are all or nothing, so this decision must be made before any symbols are added. `write::Object::add_subsection` no longer adds data to the subsection. This change was made because it was done with `append_section_data`, but this is often not the correct way to add data to the subsection. Usually `add_symbol_data` is a better choice.
For Mach-O, `add_symbol_data` now ensures that the symbol size is at least 1 when subsections via symbols are enabled. This change was made to support linking with ld-prime. It is also unclear how this previously managed to work with ld64. `write::Object::add_subsection` no longer enables subsections via symbols for Mach-O. Use `set_subsections_via_symbols` instead. This change was made because Mach-O subsections are all or nothing, so this decision must be made before any symbols are added. `write::Object::add_subsection` no longer adds data to the subsection. This change was made because it was done with `append_section_data`, but this is often not the correct way to add data to the subsection. Usually `add_symbol_data` is a better choice.
For Mach-O,
add_symbol_datanow ensures that the symbol size is at least 1 when subsections via symbols are enabled. This change was made to support linking with ld-prime. It is also unclear how this previously managed to work with ld64.write::Object::add_subsectionno longer enables subsections via symbols for Mach-O. Useset_subsections_via_symbolsinstead. This change was made because Mach-O subsections are all or nothing, so this decision must be made before any symbols are added.write::Object::add_subsectionno longer adds data to the subsection. This change was made because it was done withappend_section_data, but this is often not the correct way to add data to the subsection. Usuallyadd_symbol_datais a better choice.