gdbserver: allow agent expressions to fail with invalid memory access

This commit extends gdbserver to take account of a failed memory
access from agent_mem_read, and to return a new eval_result_type
expr_eval_invalid_memory_access.

I have only updated the agent_mem_read calls related directly to
reading memory, I have not updated any of the calls related to
tracepoint data collection.  This is just because I'm not familiar
with that area of gdb/gdbserver, and I don't want to break anything,
so leaving the existing behaviour as is seems like the safest
approach.

I've then update gdb.base/bp-cond-failure.exp to test evaluating the
breakpoints on the target, and have also extended the test so that it
checks for different sizes of memory access.

3 files changed, 17 insertions, 14 deletions

diff --git a/gdb/testsuite/gdb.base/bp-cond-failure.exp b/gdb/testsuite/gdb.base/bp-cond-failure.exp
index 6f89771d187..aa39b638592 100644
--- a/gdb/testsuite/gdb.base/bp-cond-failure.exp
+++ b/gdb/testsuite/gdb.base/bp-cond-failure.exp
@@ -39,7 +39,7 @@ if { [is_address_zero_readable] } {
 # Where the breakpoint will be placed.
 set bp_line [gdb_get_line_number "Breakpoint here"]
 
-proc run_test { cond_eval } {
+proc run_test { cond_eval access_type } {
     clean_restart ${::binfile}
 
     if {![runto_main]} {
@@ -52,7 +52,7 @@ proc run_test { cond_eval } {
     }
 
     # Setup the conditional breakpoint and record its number.
-    gdb_breakpoint "${::srcfile}:${::bp_line} if (*(int *) 0) == 0"
+    gdb_breakpoint "${::srcfile}:${::bp_line} if (*(${access_type} *) 0) == 0"
     set bp_num [get_integer_valueof "\$bpnum" "*UNKNOWN*"]
 
     gdb_test "continue" \
@@ -68,16 +68,14 @@ proc run_test { cond_eval } {
 # If we're using a remote target then conditions could be evaulated
 # locally on the host, or on the remote target.  Otherwise, conditions
 # are always evaluated locally (which is what auto will select).
-#
-# NOTE: 'target' is not included here for remote targets as a
-# gdbserver bug prevents the test from passing.  This will be fixed in
-# the next commit, and this test updated.
 if { [gdb_is_remote_or_extended_remote_target] } {
-    set cond_eval_modes { "host" }
+    set cond_eval_modes { "host" "target" }
 } else {
     set cond_eval_modes { "auto" }
 }
 
-foreach_with_prefix cond_eval $cond_eval_modes {
-    run_test $cond_eval
+foreach_with_prefix access_type { "char" "short" "int" "long long" } {
+    foreach_with_prefix cond_eval $cond_eval_modes {
+	run_test $cond_eval $access_type
+    }
 }
diff --git a/gdbserver/ax.cc b/gdbserver/ax.cc
index 38ebfbbd750..fba5b4ad0fc 100644
--- a/gdbserver/ax.cc
+++ b/gdbserver/ax.cc
@@ -1112,22 +1112,26 @@ gdb_eval_agent_expr (struct eval_agent_expr_context *ctx,
 	  break;
 
 	case gdb_agent_op_ref8:
-	  agent_mem_read (ctx, cnv.u8.bytes, (CORE_ADDR) top, 1);
+	  if (agent_mem_read (ctx, cnv.u8.bytes, (CORE_ADDR) top, 1) != 0)
+	    return expr_eval_invalid_memory_access;
 	  top = cnv.u8.val;
 	  break;
 
 	case gdb_agent_op_ref16:
-	  agent_mem_read (ctx, cnv.u16.bytes, (CORE_ADDR) top, 2);
+	  if (agent_mem_read (ctx, cnv.u16.bytes, (CORE_ADDR) top, 2) != 0)
+	    return expr_eval_invalid_memory_access;
 	  top = cnv.u16.val;
 	  break;
 
 	case gdb_agent_op_ref32:
-	  agent_mem_read (ctx, cnv.u32.bytes, (CORE_ADDR) top, 4);
+	  if (agent_mem_read (ctx, cnv.u32.bytes, (CORE_ADDR) top, 4) != 0)
+	    return expr_eval_invalid_memory_access;
 	  top = cnv.u32.val;
 	  break;
 
 	case gdb_agent_op_ref64:
-	  agent_mem_read (ctx, cnv.u64.bytes, (CORE_ADDR) top, 8);
+	  if (agent_mem_read (ctx, cnv.u64.bytes, (CORE_ADDR) top, 8) != 0)
+	    return expr_eval_invalid_memory_access;
 	  top = cnv.u64.val;
 	  break;
 
diff --git a/gdbserver/ax.h b/gdbserver/ax.h
index 8e64a7a593e..c98e36a83c6 100644
--- a/gdbserver/ax.h
+++ b/gdbserver/ax.h
@@ -41,7 +41,8 @@ enum eval_result_type
     expr_eval_unhandled_opcode,
     expr_eval_unrecognized_opcode,
     expr_eval_divide_by_zero,
-    expr_eval_invalid_goto
+    expr_eval_invalid_goto,
+    expr_eval_invalid_memory_access
   };
 
 struct agent_expr