[Dwarf-Discuss] DW_LNS_set_isa usage

Roland McGrath roland at redhat.com
Thu Jun 17 17:58:52 PDT 2010


> Not really; there's an ELF header field, e_machine, that tells you the
> architecture for the whole program, but nothing that handles the
> mixed-ISA situation.

I meant SHF_MASKPROC+n flags, if multiple ISAs are not merged into a single
section at link time, or something deep inside whatever SHT_*_ATTRIBUTES is
about or something else arch/vendor-specific like that.

> The only target I know of that actually mixes two ISAs is arm, where
> the assembler places local symbols so that external tools can tell the
> difference between arm and thumb mode. I don't believe that they use
> the isa field of the line number table for this at all.

Do you mean symbols with the STT_ARM_* types?  So that indicates a range
with st_value,st_size that is of the non-default ISA.  Is that it?

> > Are there other purposes for which DWARF consumers pay attention to isa?
> 
> We actually discussed this once in a committee meeting, and I don't
> think anyone knew of any real-world examples of its use. It's just
> something that's been there for a long time, and we haven't ever felt
> the need to remove it.

Ok.  I hadn't really noticed it there until recently, so somehow I thought
it was added in v3.


Thanks,
Roland



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