[v3] PR mi/20395 - Fix -var-update for registers in frames 1 and up

diff --git a/gdb/testsuite/gdb.mi/mi-frame-regs.exp b/gdb/testsuite/gdb.mi/mi-frame-regs.exp
new file mode 100644
index 0000000..45f81d6
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-frame-regs.exp
@@ -0,0 +1,183 @@ 
+# Copyright 1999-2016 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test essential Machine interface (MI) operations
+#
+# Verify that -var-update will provide the correct values for floating
+# and fixed varobjs that represent the pc register.
+#
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+standard_testfile basics.c
+
+if {[gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" \
+		 executable {debug}] != "" } then {
+     untested mi-frame-regs.exp
+     return -1
+}
+
+# Return the address of the specified breakpoint.
+
+proc breakpoint_address {bpnum} {
+    global hex
+    global expect_out
+    global mi_gdb_prompt
+
+    send_gdb "info breakpoint $bpnum\n"
+    gdb_expect {
+	-re ".*($hex).*$mi_gdb_prompt$" {
+	    return $expect_out(1,string)
+	}
+	-re ".*$mi_gdb_prompt$" {
+	    return ""
+	}
+	timeout {
+	    return ""
+	}
+    }
+}
+
+# Test that a floating varobj representing $pc will provide the
+# correct value via -var-update as the program stops at
+# breakpoints in different functions.
+
+proc do_floating_varobj_test {} {
+    global srcfile
+    global hex
+    global expect_out
+
+    gdb_exit
+    if {[mi_gdb_start]} then {
+	continue
+    }
+
+    with_test_prefix "floating" {
+	mi_run_to_main
+
+	# Create a floating varobj for $pc.
+	mi_gdb_test "-var-create --thread 1 --frame 0 - @ \$pc" \
+		    "\\^done,.*value=\"$hex.*" \
+	            "create varobj for pc in frame 0"
+
+	set nframes 4
+	for {set i 1} {$i < $nframes} {incr i} {
+
+	    # Run to a breakpoint in each callee function in succession.
+	    # Note that we can't use mi_runto because we need the
+	    # breakpoint to be persistent, so we can use its address.
+	    set bpnum [expr $i + 1]
+	    mi_create_breakpoint \
+	        "basics.c:callee$i" \
+		"insert breakpoint at basics.c:callee$i" \
+		-number $bpnum -func callee$i -file ".*basics.c"
+
+	    mi_execute_to "exec-continue" "breakpoint-hit" \
+			  "callee$i" ".*" ".*${srcfile}" ".*" \
+			  { "" "disp=\"keep\"" } "breakpoint hit"
+
+	    # Get the value of $pc from the floating varobj.
+	    mi_gdb_test "-var-update 1 var1" \
+			"\\^done,.*value=\"($hex) .*" \
+			"-var-update for frame $i"
+	    set pcval $expect_out(3,string)
+
+	    # Get the address of the current breakpoint.
+	    set bpaddr [breakpoint_address $bpnum]
+	    if {$bpaddr == ""} then {
+		unresolved "get address of breakpoint $bpnum"
+		return
+	    }
+
+	    # Check that the addresses are the same.
+	    if {[expr $bpaddr != $pcval]} then {
+	        fail "\$pc does not equal address of breakpoint"
+	    } else {
+	        pass "\$pc equals address of breakpoint"
+	    }
+	}
+    }
+}
+
+# Create a varobj for the pc register in each of the frames other
+# than frame 0.
+
+proc var_create_regs {nframes} {
+    global hex
+
+    for {set i 1} {$i < $nframes} {incr i} {
+	mi_gdb_test "-var-create --thread 1 --frame $i - \* \$pc" \
+		    "\\^done,.*value=\"$hex.*" \
+	            "create varobj for pc in frame $i"
+    }
+}
+
+# Check that -var-update reports that the value of the pc register
+# for each of the frames 1 and above is reported as unchanged.
+
+proc var_update_regs {nframes} {
+
+    for {set i 1} {$i < $nframes} {incr i} {
+	mi_gdb_test "-var-update 1 var$i" \
+	            "\\^done,(changelist=\\\[\\\])" \
+	            "pc unchanged in -var-update for frame $i"
+    }
+}
+
+# Test that fixed varobjs representing $pc in different stack frames
+# will provide the correct value via -var-update after the program
+# counter changes (without substantially changing the stack).
+
+proc do_fixed_varobj_test {} {
+    global srcfile
+
+    gdb_exit
+    if {[mi_gdb_start]} then {
+	continue
+    }
+
+    with_test_prefix "fixed" {
+	mi_run_to_main
+
+	# Run to the function 'callee3' so we have several frames.
+	mi_create_breakpoint "basics.c:callee3" \
+			     "insert breakpoint at basics.c:callee3" \
+			     -number 2 -func callee3 -file ".*basics.c"
+
+	mi_execute_to "exec-continue" "breakpoint-hit" \
+	              "callee3" ".*" ".*${srcfile}" ".*" \
+		      { "" "disp=\"keep\"" } "breakpoint hit"
+
+	# At the breakpoint in callee3 there are 4 frames.  Create a
+	# varobj for the pc in each of frames 1 and above.
+	set nframes 4
+	var_create_regs $nframes
+
+	# Step one instruction to change the program counter.
+	mi_execute_to "exec-next-instruction" "end-stepping-range" \
+		      "callee3" ".*" ".*${srcfile}" ".*" "" \
+		      "next instruction in callee3"
+
+	# Check that -var-update reports that the values are unchanged.
+	var_update_regs $nframes
+    }
+}
+
+do_fixed_varobj_test
+do_floating_varobj_test
+
+mi_gdb_exit
+return 0
diff --git a/gdb/varobj.c b/gdb/varobj.c
index fb1349a..80738af 100644
--- a/gdb/varobj.c
+++ b/gdb/varobj.c
@@ -348,6 +348,14 @@  varobj_create (char *objname,
 			      " as an expression.\n");
 	  return NULL;
 	}
+      else if (var->root->exp->elts[0].opcode == OP_REGISTER)
+	{
+	  /* Force the scope of a register varobj to be the global
+	     block.  This allows it to be associated with a frame
+	     and a thread.  */
+	  gdb_assert (innermost_block == NULL);
+	  innermost_block = block_global_block (block);
+	}
 
       var->format = variable_default_display (var);
       var->root->valid_block = innermost_block;