[PATCH] D60189: [llvm-objcopy] Simplify SHT_NOBITS -> SHT_PROGBITS promotion

[James Henderson via Phabricator via llvm-commits]

jhenderson added a comment.

I'm trying to think where a NOBITS/PROGBITS distinction actually matters. Some relevant thoughts come to my mind:

1. Where sections are in the middle of segments, they should always be PROGBITS, not NOBITS, otherwise addresses will get messed up (there is a special exception for .tbss and nested PT_TLS segments).
2. If a section is PROGBITS when it doesn't need to be, then it will take up file space. Assuming it is filled with zeroes, this is harmless in terms of how the ELF behaves, and just impacts things like file size and probably load times.
3. Converting a PROGBITS section to NOBITS can be harmful if the contents are important, as those contents will be lost.
4. Non-alloc NOBITS sections are meaningless. Promoting them to PROGBITS will bloat the file size but otherwise have no effect.
5. If there is a GNU binutils test for it, there's probably some good reason for any behaviour that I haven't thought of, so we should match GNU's behaviour, unless it is clearly dodgy.

Points 1-4 indicate to me that promoting NOBITS to PROGBITS under more cases is probably fine, as long as point 5 is observed.


Repository:
  rL LLVM

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https://reviews.llvm.org/D60189