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I am less sanguine about updating the tracepoint code, I suppose because it is pretty new and yet doesn't implement even what was already in gdb when it went in:
if (bytes != 4)
error (_("DW_OP_piece %s not supported in location for \"%s\"."),
pulongest (bytes), SYMBOL_PRINT_NAME (symbol));
I did dig around in the code a little, and it turns out I'm also not clear on all the details I would need to implement the support.
I don't really see how DWARF expressions can work with the current setup. Maybe just some subset can -- but then I would like to understand how the subset is chosen, I guess so I can argue against choosing DW_OP_bit_piece ;-). Ok, seriously...
For instance, I don't understand how a DWARF expression involving a conditional could work. You could compile DWARF to AX, including the condition. But then I think you'd have to circumvent the DWARF expression when re-evaluating the expression at "replay" time (I don't know the real name of the mode, sorry).
GCC is already emitting nontrivial DWARF. It can emit some stack ops
(look at the MOD case in dwarf2out.c). It can emit pieces and stack and
literal values. And, I think it can emit TLS references. So this is
not just hypothetical, today's expression translation is already
insufficient for today's GCC.
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