Should a DW_OP_implicit_value be taken from the left end?

[Andreas Arnez <arnez@linux.vnet.ibm.com>]

The following patch changed how sub-values of a DW_OP_implicit_value are
extracted on big-endian platforms:

  https://sourceware.org/ml/gdb-patches/2011-08/msg00123.html

The patch seems to assume that the placement rule is similar as for
DW_OP_stack_value.  I think that's wrong; DW_OP_implicit_value should
always be taken from the left end.  (See rationale below for an
explanation.)  And I'd like to know whether anyone objects.

I'm in the process of preparing a patch series for fixing various
problems with DWARF piece handling, and the series currently contains a
patch for reverting the above patch's effect on DW_OP_implicit_value.

Rationale:

Since DW_OP_implicit_value can express arbitrary amounts of structured
or unstructured data, the notion of a "least significant byte" is
meaningless.  The patch above makes it impossible for a
DW_OP_implicit_pointer operation to refer to any sub-value within a
DW_OP_implicit_value on big-endian targets.

E.g., consider this code snippet:

  const char foo[] = "Hello, world!";
  char *a = &foo[0];
  char *b = &foo[7];

IMHO the compiler should be able to describe `foo' with a single
DW_OP_implicit_value operation and `a' and `b' as DW_OP_implicit_pointer
operations pointing into that value.

Any objections?

--
Andreas