libdwfl stores registers in an array of uint64_t indexed by the DWARF
register number. This is suboptimal for a couple of reasons:
1. Although the DWARF specification states that registers should be
numbered for "optimal density", in practice this isn't the case. ABIs
include unused ranges of numbers and don't order registers based on
how likely they are to be known (e.g., caller-saved registers usually
aren't recovered while unwinding the stack, but they are often
numbered before callee-saved registers).
2. This precludes support for registers larger than 64 bits, like SSE
registers.
For our own unwinder, we want to store registers in an
architecture-specific format to solve both of these problems.
So, have each architecture define its layout with registers arranged for
space efficiency and convenience when parsing saved registers from core
dumps. Instead of generating an arch_foo.c file from arch_foo.c.in,
separately define the logical register order in an arch_foo.defs file,
and use it to generate an arch_foo.inc file that is included from
arch_foo.c. The layout is defined as a macro in arch_foo.c. While we're
here, drop some register definitions that aren't useful at the moment.
Then, define struct drgn_register_state to efficiently store registers
in the defined format.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
