[RFC][PATCH v2][PR remote/16896] Invalidate a register in cache when a remote target failed to write it.

[Pierre Langlois <pierre dot langlois at embecosm dot com>]

Hello all,

This patch addresses the issue in patch [1] generically as pointed out by
a comment [2].

As opposed to invalidating a register in cache in the remote target before
throwing an error, we can do this using a cleanup in regcache_raw_write.  This
patch adds routines to add a regcache_invalidate cleanup to the current chain.
We can use this before target_store_registers and discard it after if an error
was not thrown.

[1] https://sourceware.org/ml/gdb-patches/2014-05/msg00083.html
[2] https://sourceware.org/ml/gdb-patches/2014-05/msg00357.html

2014-05-20  Pierre Langlois  <pierre.langlois@embecosm.com>

	PR remote/16896
	* regcache.c (register_to_invalidate): New structure. Combines a pointer
        to a struct regcache and a register number.
	(do_register_invalidate): New function. Call regcache_invalidate.
	(make_cleanup_regcache_invalidate): New function. Construct a cleanup
        for invalidating a register.
	(regcache_raw_write): Call make_cleanup_regcache_invalidate
	* regcache.h (make_cleanup_regcache_invalidate): New prototype.

---
 gdb/regcache.c | 41 ++++++++++++++++++++++++++++++++++++++---
 gdb/regcache.h |  2 ++
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/gdb/regcache.c b/gdb/regcache.c
index 8b588c6..87a6b02 100644
--- a/gdb/regcache.c
+++ b/gdb/regcache.c
@@ -267,6 +267,30 @@ make_cleanup_regcache_xfree (struct regcache *regcache)
   return make_cleanup (do_regcache_xfree, regcache);
 }
 
+/* Cleanup routines for invalidating a register.  */
+
+struct register_to_invalidate
+{
+  struct regcache *regcache;
+  int regnum;
+};
+
+static void
+do_regcache_invalidate (void *data)
+{
+  struct register_to_invalidate *reg = data;
+  regcache_invalidate (reg->regcache, reg->regnum);
+}
+
+struct cleanup *
+make_cleanup_regcache_invalidate (struct regcache *regcache, int regnum)
+{
+  struct register_to_invalidate* reg = XNEW (struct register_to_invalidate);
+  reg->regcache = regcache;
+  reg->regnum = regnum;
+  return make_cleanup_dtor (do_regcache_invalidate, (void *) reg, xfree);
+}
+
 /* Return REGCACHE's architecture.  */
 
 struct gdbarch *
@@ -846,7 +870,8 @@ void
 regcache_raw_write (struct regcache *regcache, int regnum,
 		    const gdb_byte *buf)
 {
-  struct cleanup *old_chain;
+  struct cleanup *chain_before_save_inferior;
+  struct cleanup *chain_before_invalidate_register;
 
   gdb_assert (regcache != NULL && buf != NULL);
   gdb_assert (regnum >= 0 && regnum < regcache->descr->nr_raw_registers);
@@ -864,16 +889,26 @@ regcache_raw_write (struct regcache *regcache, int regnum,
 		  regcache->descr->sizeof_register[regnum]) == 0))
     return;
 
-  old_chain = save_inferior_ptid ();
+  chain_before_save_inferior = save_inferior_ptid ();
   inferior_ptid = regcache->ptid;
 
   target_prepare_to_store (regcache);
   memcpy (register_buffer (regcache, regnum), buf,
 	  regcache->descr->sizeof_register[regnum]);
   regcache->register_status[regnum] = REG_VALID;
+
+  /* Register a cleanup function for invalidating the register after it is
+     written, in case of a failure.  */
+  chain_before_invalidate_register =
+    make_cleanup_regcache_invalidate (regcache, regnum);
+
   target_store_registers (regcache, regnum);
 
-  do_cleanups (old_chain);
+  /* The target did not throw an error so we can discard invalidating the
+     register and restore the cleanup chain to what it was.  */
+  discard_cleanups (chain_before_invalidate_register);
+
+  do_cleanups (chain_before_save_inferior);
 }
 
 void
diff --git a/gdb/regcache.h b/gdb/regcache.h
index 8423f57..bb40b65 100644
--- a/gdb/regcache.h
+++ b/gdb/regcache.h
@@ -33,6 +33,8 @@ extern struct regcache *get_thread_arch_aspace_regcache (ptid_t,
 
 void regcache_xfree (struct regcache *regcache);
 struct cleanup *make_cleanup_regcache_xfree (struct regcache *regcache);
+struct cleanup *make_cleanup_regcache_invalidate (struct regcache *regcache,
+						  int regnum);
 struct regcache *regcache_xmalloc (struct gdbarch *gdbarch,
 				   struct address_space *aspace);
 
--
1.9.0