[PATCH] D99250: [DebugInfo] Fix the mismatching of C++ language tags and Dwarf versions.

[Paul Robinson via Phabricator via cfe-commits]

probinson added a comment.

I think there are degrees of compatibility with regard to DWARF, which is inherently supposed to be extensible if the extension can be safely ignored by a consumer.  This is the "permissive" rule in the standard.

- A new FORM must *never* be used, because that makes it impossible to interpret the rest of the CU.
- A new attribute or tag may be used if it can be safely ignored.
- A new constant value for an existing attribute also may be used if it can be safely ignored.

For other cases, such as using existing forms/attributes in novel ways, it really depends on how we think (or know) consumers will react to it.   DW_AT_high_pc with a constant value is an excellent example; a debugger would not have any obvious reasonable interpretation for that.  On the other hand, something like a new language code happens all the time, and there's even a range for user-defined language codes.  A debugger must be prepared for unknown values, and an unknown value inside the standard-defined range doesn't seem like a reason to crash, or even bail out.

If we implemented a "strict DWARF" mode, then in that mode we should be more careful about this.  If you are implementing a DWARF verifier, it would be reasonable to report using language codes outside the range defined by a given DWARF version IMO, but a bug report about that would likely be rejected.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D99250/new/

https://reviews.llvm.org/D99250