On Thu, Mar 11, 2021 at 11:44 AM Jakub Jelinek <ja...@redhat.com> wrote:
> On Thu, Mar 11, 2021 at 11:30:05AM -0800, David Blaikie wrote: > > Thanks! - is this proposed as a DWARF extension? I thought I remembered > it > > 170427.1 I think. Note, what is emitted is different from what is being > proposed, the problem with DW_LLE_* and DW_RLE_* is that they aren't easily > extensible (in a way that would allow consumers that don't know about the > extension skip it and parse just the standard ones; because when seeing > an unknown opcode, the consumer doesn't know what arguments if any it has). > E.g. in the way .debug_macro allows producers to define what arguments > extension opcodes have (how many and what DW_FORM_* each has). > So I think what GCC currently produces puts the stuff before the location > sequences such that if a consumer can't handle those, it can skip those. > Ah, cunning! Yeah, there's a few places where LLVM just keeps trying to parse the next thing, rather than only parsing parts that are referenced from elsewhere (the other one I know of is a bug in location lists when combined with bfd's linker tombstoning of gc'd sections (it sets any relocation to a gc'd section to zero): if a location list were to span across a gc'd section (such as for a global, raised into a register in one function - LLVM can't produce the right DWARF for this, not sure about GCC) binutils readelf, etc, will only dump sections of debug_loc that are referenced from .debug_info, so the early list termination just leaves holes, rather than mangled parsing trying to interpret the location expression following the accidental terminator as the start of another location list) > The only thing that doesn't really work well for consumer unaware about > that > extension is walking the whole .debug_rnglists and dumping everything that > it contains. > Yup - yeah, LLVM will just try to parse each offset and then go to the next one, etc. (I don't think lldb would do this, hopefully - this is only an issue with llvm-dwarfdump trying to dump as much as possible) - Dave
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