gdb: use reg_buffer_common throughout gdbsupport/common-regcache.h

Right now, gdbsupport/common-regcache.h contains two abstractons for a
regcache.  An opaque type `regcache` (gdb and gdbserver both have their
own regcache that is the concrete version of this) and an abstract base
class `reg_buffer_common`, that is the base of regcaches on both sides.
These abstractions allow code to be written for both gdb and gdbserver,
for instance in the gdb/arch sub-directory.

However, having two
different abstractions is impractical.  If some common code has a regcache,
and wants to use an operation defined on reg_buffer_common, it can't.
It would be better to have just one.  Change all instances of `regcache
*` in gdbsupport/common-regcache.h to be `reg_buffer_common *`, then fix
fallouts.

Implementations in gdb and gdbserver now need to down-cast (using
gdb::checked_static_cast) from reg_buffer_common to their concrete
regcache type.  Some of them could be avoided by changing free functions
(like regcache_register_size) to be virtual methods on
reg_buffer_common.  I tried it, it seems to work, but I did not include
it in this series to avoid adding unnecessary changes.

Change-Id: Ia5503adb6b5509a0f4604bd2a68b4642cc5283fd
Reviewed-by: John Baldwin <jhb@FreeBSD.org>

2 files changed, 14 insertions, 7 deletions

diff --git a/gdbserver/linux-arm-low.cc b/gdbserver/linux-arm-low.cc
index 5975b44..0a6f362 100644
--- a/gdbserver/linux-arm-low.cc
+++ b/gdbserver/linux-arm-low.cc
@@ -24,6 +24,7 @@
 #include "linux-aarch32-low.h"
 #include "linux-aarch32-tdesc.h"
 #include "linux-arm-tdesc.h"
+#include "gdbsupport/gdb-checked-static-cast.h"
 
 #include <sys/uio.h>
 /* Don't include elf.h if linux/elf.h got included by gdb_proc_service.h.
@@ -913,7 +914,8 @@ get_next_pcs_syscall_next_pc (struct arm_get_next_pcs *self)
   CORE_ADDR pc = regcache_read_pc (self->regcache);
   int is_thumb = arm_is_thumb_mode ();
   ULONGEST svc_number = 0;
-  struct regcache *regcache = self->regcache;
+  regcache *regcache
+    = gdb::checked_static_cast<struct regcache *> (self->regcache);
 
   if (is_thumb)
     {
diff --git a/gdbserver/regcache.cc b/gdbserver/regcache.cc
index 2e75a94..823ea1f 100644
--- a/gdbserver/regcache.cc
+++ b/gdbserver/regcache.cc
@@ -21,6 +21,8 @@
 #include "gdbthread.h"
 #include "tdesc.h"
 #include "gdbsupport/rsp-low.h"
+#include "gdbsupport/gdb-checked-static-cast.h"
+
 #ifndef IN_PROCESS_AGENT
 
 struct regcache *
@@ -64,7 +66,7 @@ get_thread_regcache (struct thread_info *thread, int fetch)
 
 /* See gdbsupport/common-regcache.h.  */
 
-struct regcache *
+reg_buffer_common *
 get_thread_regcache_for_ptid (ptid_t ptid)
 {
   return get_thread_regcache (find_thread_ptid (ptid), 1);
@@ -307,9 +309,10 @@ register_size (const struct target_desc *tdesc, int n)
 /* See gdbsupport/common-regcache.h.  */
 
 int
-regcache_register_size (const struct regcache *regcache, int n)
+regcache_register_size (const reg_buffer_common *regcache, int n)
 {
-  return register_size (regcache->tdesc, n);
+  return register_size
+    (gdb::checked_static_cast<const struct regcache *> (regcache)->tdesc, n);
 }
 
 static unsigned char *
@@ -437,10 +440,11 @@ regcache::raw_collect (int n, void *buf) const
 }
 
 enum register_status
-regcache_raw_read_unsigned (struct regcache *regcache, int regnum,
+regcache_raw_read_unsigned (reg_buffer_common *reg_buf, int regnum,
 			    ULONGEST *val)
 {
   int size;
+  regcache *regcache = gdb::checked_static_cast<struct regcache *> (reg_buf);
 
   gdb_assert (regcache != NULL);
 
@@ -486,9 +490,10 @@ collect_register_by_name (struct regcache *regcache,
 /* Special handling for register PC.  */
 
 CORE_ADDR
-regcache_read_pc (struct regcache *regcache)
+regcache_read_pc (reg_buffer_common *regcache)
 {
-  return the_target->read_pc (regcache);
+  return the_target->read_pc
+    (gdb::checked_static_cast<struct regcache *> (regcache));
 }
 
 void