[Dwarf-Discuss] DW_LNS_set_isa usage

Roland McGrath roland at redhat.com
Thu Jun 17 16:27:04 PDT 2010


I've never seen DW_LNS_set_isa used.  GCC doesn't generate it.
GAS can be told to generate it with its .loc directive, but that
usage is hard to grep for in code and I don't know what corpus
of assembly to search in anyway.  GDB doesn't pay attention to it.

The specification is fairly clear on the meaning of the isa field for line
information.  But I'm only guessing as to how people actually make use of
the information.  Is it just so that disassembly or breakpoint insertion
keyed off source line locations knows what ISA to interpret it as?  In
multi-ISA targets, what do debuggers (and people) do if there is no DWARF
information for an address?  Don't you have to know the ISA that applies by
some external means anyway?  i.e., if following a PC found in machine
state, you know what ISA that machine is supposed to be executing.  If
looking at an object file statically, isn't there something like
arch-specific ELF section flags that tells you?

Are there other purposes for which DWARF consumers pay attention to isa?


Thanks,
Roland



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