d7d1337368
To return DWARF attribute values, debug/dwarf maps the DWARF attribute value classes to Go types. Unfortunately, this mapping is ambiguous in a way that makes it impossible to correctly interpret some DWARF attributes as of DWARF 4. For example, AttrStartScope can be either a constant or a rangelistptr. The attribute is interpreted differently depending on its class, but debug/dwarf maps both classes to int64, so the caller can't distinguish them from the Go type. AttrDataMemberLocation is similar. To address this, this change adds a field to type Field that indicates the exact DWARF attribute value class of that field's value. This makes it possible to distinguish value classes that can't be distinguished by their Go type alone. The root of this type ambiguity was DWARF itself. For example, DWARF 2 made no distinction between constants that were just constants and constants that were section offsets because no attribute could have both meanings. Hence, the single int64 type was sufficient. To avoid introducing just another layer of ambiguity, this change takes pains to canonicalize ambiguous classes in DWARF 2 and 3 files into the unambiguous classes of DWARF 4. Of course, there's no guarantee that future DWARF versions won't do the same thing again and further subdivide the DWARF 4 classes. This change gets ahead of this somewhat by distinguishing the various *ptr classes even though the encoding does not. If there's some other form of split, we can handle this in a backwards-compatible way by introducing, for example, a Class5 field and type. Change-Id: I4ef96d1223b0fd7f96ecf44fcc0e704a36af02b4 Reviewed-on: https://go-review.googlesource.com/8502 Reviewed-by: Ian Lance Taylor <iant@golang.org> |
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