[Dwarf-Discuss] DW_LNS_set_isa usage

Nathan Froyd froydnj at codesourcery.com
Thu Jun 17 18:43:36 PDT 2010


On Thu, Jun 17, 2010 at 05:16:19PM -0700, Cary Coutant wrote:
> > 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?
> 
> 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.

MIPS mixes ISAs as well: MIPS{32,64} and MIPS16/microMIPS (once
microMIPS support is checked in, anyway).  But MIPS doesn't use the isa
field either, so far as I know.

-Nathan



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