[PATCH v3 2/3] gdbserver: Prevent stale/random values in register cache

[Andreas Arnez <arnez at linux dot vnet dot ibm dot com>]

When fetch_inferior_registers does not update all registers, this
patch assures that no stale register values remain in the register
cache.  On Linux platforms using the regsets interface, when one of
the ptrace calls used for fetching the register values returns an
error, this patch also avoids copying the random data returned from
ptrace into the register cache.  All unfetched registers are marked
"unavailable" instead.

gdb/gdbserver/ChangeLog:

	* linux-low.c (regsets_fetch_inferior_registers): Do not invoke
	the regset's store function when ptrace returned an error.
	* regcache.c (get_thread_regcache): Invalidate register cache
	before fetching inferior's registers.
---
 gdb/gdbserver/linux-low.c |   11 ++++++-----
 gdb/gdbserver/regcache.c  |    5 +++++
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 164b0f6..c1b53ff 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -4255,8 +4255,6 @@ regsets_fetch_inferior_registers (struct regsets_info *regsets_info,
 	      /* If we get EIO on a regset, do not try it again for
 		 this process mode.  */
 	      disable_regset (regsets_info, regset);
-	      free (buf);
-	      continue;
 	    }
 	  else
 	    {
@@ -4266,9 +4264,12 @@ regsets_fetch_inferior_registers (struct regsets_info *regsets_info,
 	      perror (s);
 	    }
 	}
-      else if (regset->type == GENERAL_REGS)
-	saw_general_regs = 1;
-      regset->store_function (regcache, buf);
+      else
+	{
+	  if (regset->type == GENERAL_REGS)
+	    saw_general_regs = 1;
+	  regset->store_function (regcache, buf);
+	}
       free (buf);
     }
   if (saw_general_regs)
diff --git a/gdb/gdbserver/regcache.c b/gdb/gdbserver/regcache.c
index 718ae8c..4ea16a6 100644
--- a/gdb/gdbserver/regcache.c
+++ b/gdb/gdbserver/regcache.c
@@ -52,6 +52,11 @@ get_thread_regcache (struct thread_info *thread, int fetch)
       struct thread_info *saved_thread = current_thread;
 
       current_thread = thread;
+#ifndef IN_PROCESS_AGENT
+      /* Invalidate all registers, to prevent stale left-overs.  */
+      memset (regcache->register_status, REG_UNAVAILABLE,
+	      regcache->tdesc->num_registers);
+#endif
       fetch_inferior_registers (regcache, -1);
       current_thread = saved_thread;
       regcache->registers_valid = 1;
-- 
1.7.9.5