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, 11 insertions, 8 deletions

diff --git a/gdbsupport/common-regcache.cc b/gdbsupport/common-regcache.cc
index 3515bed..b6f02ba 100644
--- a/gdbsupport/common-regcache.cc
+++ b/gdbsupport/common-regcache.cc
@@ -23,7 +23,7 @@
 /* Return the register's value or throw if it's not available.  */
 
 ULONGEST
-regcache_raw_get_unsigned (struct regcache *regcache, int regnum)
+regcache_raw_get_unsigned (reg_buffer_common *regcache, int regnum)
 {
   ULONGEST value;
   enum register_status status;
diff --git a/gdbsupport/common-regcache.h b/gdbsupport/common-regcache.h
index e462f53..6d98ca8 100644
--- a/gdbsupport/common-regcache.h
+++ b/gdbsupport/common-regcache.h
@@ -20,6 +20,8 @@
 #ifndef COMMON_COMMON_REGCACHE_H
 #define COMMON_COMMON_REGCACHE_H
 
+struct reg_buffer_common;
+
 /* This header is a stopgap until we have an independent regcache.  */
 
 enum register_status : signed char
@@ -44,28 +46,29 @@ enum register_status : signed char
    thread specified by PTID.  This function must be provided by
    the client.  */
 
-extern struct regcache *get_thread_regcache_for_ptid (ptid_t ptid);
+extern reg_buffer_common *get_thread_regcache_for_ptid (ptid_t ptid);
 
 /* Return the size of register numbered N in REGCACHE.  This function
    must be provided by the client.  */
 
-extern int regcache_register_size (const struct regcache *regcache, int n);
+extern int regcache_register_size (const reg_buffer_common *regcache, int n);
 
 /* Read the PC register.  This function must be provided by the
    client.  */
 
-extern CORE_ADDR regcache_read_pc (struct regcache *regcache);
+extern CORE_ADDR regcache_read_pc (reg_buffer_common *regcache);
 
 /* Read the PC register.  If PC cannot be read, return 0.
    This is a wrapper around 'regcache_read_pc'.  */
 
-extern CORE_ADDR regcache_read_pc_protected (regcache *regcache);
+extern CORE_ADDR regcache_read_pc_protected (reg_buffer_common *regcache);
 
 /* Read a raw register into a unsigned integer.  */
-extern enum register_status regcache_raw_read_unsigned
-  (struct regcache *regcache, int regnum, ULONGEST *val);
+extern enum register_status
+regcache_raw_read_unsigned (reg_buffer_common *regcache, int regnum,
+			    ULONGEST *val);
 
-ULONGEST regcache_raw_get_unsigned (struct regcache *regcache, int regnum);
+ULONGEST regcache_raw_get_unsigned (reg_buffer_common *regcache, int regnum);
 
 struct reg_buffer_common
 {