[PATCH] D73999: [MC][ELF] Warn changed section type or flags

[Peter Smith via Phabricator via llvm-commits]

psmith added a comment.

In D73999#1866168 <https://reviews.llvm.org/D73999#1866168>, @MaskRay wrote:

> Address review comments.
>
> I tend to agree with Alan Modra's arguement in
>  https://sourceware.org/ml/binutils/2020-02/msg00093.html
>
> > I don't think so.  User assembly often gets section attributes wrong
> >  or leaves them off entirely for special sections known to the
> >  assembler.  ie. the first .section .foo above is a built-in rather
> >  than user input.
>
> Add more folks for feedback.
>
> Please see my binutils post. For a .section directive with the same name but a different field. If the field is:
>
> - sh_flags or sh_type: warn
> - sh_link due to SHF_LINK_ORDER: no warning. produce separate sections
> - sh_entsize due to SHF_MERGE: still controversial


I agree with warning for sh_flags, I think there is too much legacy code out there that would behave differently.
I agree with sh_link producing separate sections. In an ideal world no-one writes this by hand in assembly.
For sh_entsize SHF_MERGE, this is informing the linker that it can produce an optimisation, which it is permitted to ignore. I tend towards an error message if it is implementable as it is a strong message to fix the assembler. The next best thing is a warning then clearing SHF_MERGE and setting sh_entsize to 0. I don't think a warning on its own is safe.


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