[Bug tdep/29804] New: [gdb/tdep, vax] Remove gdbarch_deprecated_function_start_offset

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29804

            Bug ID: 29804
           Summary: [gdb/tdep, vax] Remove
                    gdbarch_deprecated_function_start_offset
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tdep
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

As noted in PR29793, there's only one user left of
gdbarch_deprecated_function_start_offset:
...
$ find gdb -type f | xargs grep set_gdbarch_deprecated_function_start_offset
gdb/gdbarch-gen.h:extern void set_gdbarch_deprecated_function_start_offset
(struct gdbarch *gdbarch, CORE_ADDR deprecated_function_start_offset);
gdb/vax-tdep.c:  set_gdbarch_deprecated_function_start_offset (gdbarch, 2);
gdb/gdbarch.c:set_gdbarch_deprecated_function_start_offset (struct gdbarch
*gdbarch,
...

The vax target.

The deprecation started in 2004:
...
2004-06-18  Andrew Cagney  <cagney@gnu.org>

        * gdbarch.sh (DEPRECATED_FUNCTION_START_OFFSET): Deprecated.
...

The submission email (
https://sourceware.org/pipermail/gdb-patches/2004-May/034563.html ) mentions
vax:
...
The VAX uses this to ``adjust'' a function 
pointer so that it instead points to the function's code address (the 
first few bytes of a vax function are not executable and need to be 
skipped over).

Thing is, this conversion is exactly what CONVERT_FUNC_PTR_ADDR is for. 
  Given a function pointer return the function's code address.  Given 
this overlap, I think FUNCTION_START_OFFSET should be deprecated - it is 
redundant.
...

Unfortunately grepping through the sources shows that code locations of 
gdbarch_deprecated_function_start_offset and convert_from_func_ptr_addr don't
always overlap, so this is not a mechanical substitution, and needs to be
tested.

One outcome could be that we cannot (fully) remove it, but then we should
de-deprecate it and document precisely why we need it and when and where this
hook is necessary.

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