gdb: fix gdbarch_tdep ODR violation

I would like to be able to use non-trivial types in gdbarch_tdep types.
This is not possible at the moment (in theory), because of the one
definition rule.

To allow it, rename all gdbarch_tdep types to <arch>_gdbarch_tdep, and
make them inherit from a gdbarch_tdep base class.  The inheritance is
necessary to be able to pass pointers to all these <arch>_gdbarch_tdep
objects to gdbarch_alloc, which takes a pointer to gdbarch_tdep.

These objects are never deleted through a base class pointer, so I
didn't include a virtual destructor.  In the future, if gdbarch objects
deletable, I could imagine that the gdbarch_tdep objects could become
owned by the gdbarch objects, and then it would become useful to have a
virtual destructor (so that the gdbarch object can delete the owned
gdbarch_tdep object).  But that's not necessary right now.

It turns out that RISC-V already has a gdbarch_tdep that is
non-default-constructible, so that provides a good motivation for this
change.

Most changes are fairly straightforward, mostly needing to add some
casts all over the place.  There is however the xtensa architecture,
doing its own little weird thing to define its gdbarch_tdep.  I did my
best to adapt it, but I can't test those changes.

Change-Id: Ic001903f91ddd106bd6ca09a79dabe8df2d69f3b

1 files changed, 6 insertions, 4 deletions

diff --git a/gdb/nios2-tdep.h b/gdb/nios2-tdep.h
index f9e7349f0f5..96f186536e6 100644
--- a/gdb/nios2-tdep.h
+++ b/gdb/nios2-tdep.h
@@ -20,6 +20,8 @@
 #ifndef NIOS2_TDEP_H
 #define NIOS2_TDEP_H
 
+#include "gdbarch.h"
+
 /* Nios II ISA specific encodings and macros.  */
 #include "opcode/nios2.h"
 
@@ -67,19 +69,19 @@
 #define NIOS2_CDX_OPCODE_SIZE 2
 
 /* Target-dependent structure in gdbarch.  */
-struct gdbarch_tdep
+struct nios2_gdbarch_tdep : gdbarch_tdep
 {
   /* Assumes FRAME is stopped at a syscall (trap) instruction; returns
      the expected next PC.  */
   CORE_ADDR (*syscall_next_pc) (struct frame_info *frame,
-				const struct nios2_opcode *op);
+				const struct nios2_opcode *op) = nullptr;
 
   /* Returns true if PC points to a kernel helper function.  */
-  bool (*is_kernel_helper) (CORE_ADDR pc);
+  bool (*is_kernel_helper) (CORE_ADDR pc) = nullptr;
 
   /* Offset to PC value in jump buffer.
      If this is negative, longjmp support will be disabled.  */
-  int jb_pc;
+  int jb_pc = 0;
 };
 
 extern struct target_desc *tdesc_nios2_linux;