[PATCHv5 3/5] gdb: PR mi/20395: Fix -var-update for registers in frames 1 and up

[Andrew Burgess <andrew dot burgess at embecosm dot com>]

When revising this patch Simon talked about using DEF_ENUM_FLAGS_TYPE
for the 'track_type', but that doesn't seem to work for enums nested
within a class (as he pointed out).

I'm happy to move the enum innermost_block_tracker::track_type out of
the class, and make it global (with a more descriptive name I guess)
if that's what people would prefer, then I could use
DEF_ENUM_FLAGS_TYPE.

Otherwise, I think all of the review comments have been addressed.

Thanks,
Andrew

---

This patch fixes a problem with using the MI -var-update command
to access the values of registers in frames other than the current
frame.  The patch includes a test that demonstrates the problem:

* run so there are several frames on the stack
* create a fixed varobj for $pc in each frame, #'s 1 and above
* step one instruction, to modify the value of $pc
* call -var-update for each of the previously created varobjs
  to verify that they are not reported as having changed.

Without the patch, the -var-update command reported that $pc for all
frames 1 and above had changed to the value of $pc in frame 0.

A varobj is created as either fixed, the expression is evaluated within
the context of a specific frame, or floating, the expression is
evaluated within the current frame, whatever that may be.

When a varobj is created by -var-create we set two fields of the varobj
to track the context in which the varobj was created, these two fields
are varobj->root->frame and var->root->valid_block.

If a varobj is of type fixed, then, when we subsequently try to
reevaluate the expression associated with the varobj we must determine
if the original frame (and block) is still available, if it is not then
the varobj can no longer be evaluated.

The problem is that for register expressions varobj->root->valid_block
is not set correctly.  This block tracking is done using the global
'innermost_block' which is set in the various parser files (for example
c-exp.y).  However, this is not set for register expressions.

The fix then seems like it should be to just update the innermost block
when parsing register expressions, however, that solution causes several
test regressions.

The problem is that in some cases we rely on the expression parsing
code not updating the innermost block for registers, one example is
when we parse the expression for a 'display' command.  The display
commands treats registers like floating varobjs, but symbols are
treated like fixed varobjs.  So 'display $reg_name' will always show
the value of '$reg_name' even as the user moves from frame to frame,
while 'display my_variable' will only show 'my_variable' while it is
in the current frame and/or block, when the user moves to a new frame
and/or block (even one with a different 'my_variable' in) then the
display of 'my_variable' stops.  For the case of 'display', without
the option to force fixed or floating expressions, the current
behaviour is probably the best choice.  For the varobj system though,
we can choose between floating and fixed, and we should try to make
this work for registers.

There's only one existing test case that needs to be updated, in that
test a fixed varobj is created using a register, the MI output now
include the thread-id in which the varobj should be evaluated, which I
believe is correct behaviour.  I also added a new floating test case
into the same test script, however, right now this also includes the
thread-id in the expected output, which I believe is an existing gdb
bug, which I plan to fix next.

Tested on x86_64 Linux native and native-gdbserver, no regressions.

gdb/ChangeLog:

	PR mi/20395
	* ada-exp.y (write_var_from_sym): Pass extra parameter when
	updating innermost block.
	* parse.c (innermost_block_tracker::update): Take extra type
	parameter, and check types match before updating innermost block.
	(write_dollar_variable): Update innermost block for registers.
	* parser-defs.h (enum innermost_block_tracker::track_type): New.
	(innermost_block_tracker::reset): Take type parameter.
	(innermost_block_tracker::update): Take type parameter, and pass
	type through as needed.
	(innermost_block_tracker::type): New member.
	(operator|): New function for innermost_block_tracker::track_type.
	* varobj.c (varobj_create): Pass type when reseting innermost
	block.

gdb/testsuite/ChangeLog:

	* gdb.mi/basics.c: Add new global.
	* gdb.mi/mi-frame-regs.exp: New file.
	* gdb.mi/mi-var-create-rtti.exp: Update expected results, add new
	case.
---
 gdb/ChangeLog                               |  17 +++
 gdb/ada-exp.y                               |   2 +-
 gdb/parse.c                                 |   9 +-
 gdb/parser-defs.h                           |  24 +++-
 gdb/testsuite/ChangeLog                     |   8 ++
 gdb/testsuite/gdb.mi/basics.c               |   2 +
 gdb/testsuite/gdb.mi/mi-frame-regs.exp      | 186 ++++++++++++++++++++++++++++
 gdb/testsuite/gdb.mi/mi-var-create-rtti.exp |   5 +-
 gdb/varobj.c                                |   3 +-
 9 files changed, 248 insertions(+), 8 deletions(-)
 create mode 100644 gdb/testsuite/gdb.mi/mi-frame-regs.exp

diff --git a/gdb/ada-exp.y b/gdb/ada-exp.y
index fa7a4d5b4e8..7500e7e4438 100644
--- a/gdb/ada-exp.y
+++ b/gdb/ada-exp.y
@@ -757,7 +757,7 @@ write_var_from_sym (struct parser_state *par_state,
 		    struct symbol *sym)
 {
   if (symbol_read_needs_frame (sym))
-    innermost_block.update (block);
+    innermost_block.update (block, innermost_block_tracker::for_symbols);
 
   write_exp_elt_opcode (par_state, OP_VAR_VALUE);
   write_exp_elt_block (par_state, block);
diff --git a/gdb/parse.c b/gdb/parse.c
index 042df51bf8a..0abfed13962 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -126,9 +126,12 @@ static expression_up parse_exp_in_context_1 (const char **, CORE_ADDR,
    the currently stored block, or if no block is stored yet.  */
 
 void
-innermost_block_tracker::update (const struct block *b)
+innermost_block_tracker::update (const struct block *b,
+				 enum innermost_block_tracker::track_type t)
 {
-  if (m_innermost_block == NULL || contained_in (b, m_innermost_block))
+  if ((m_type & t) != 0
+      && (m_innermost_block == NULL
+	  || contained_in (b, m_innermost_block)))
     m_innermost_block = b;
 }
 
@@ -693,6 +696,8 @@ handle_register:
   str.ptr++;
   write_exp_string (ps, str);
   write_exp_elt_opcode (ps, OP_REGISTER);
+  innermost_block.update (expression_context_block,
+			  innermost_block_tracker::for_registers);
   return;
 }
 
diff --git a/gdb/parser-defs.h b/gdb/parser-defs.h
index 5265b394bea..36741ad050b 100644
--- a/gdb/parser-defs.h
+++ b/gdb/parser-defs.h
@@ -81,20 +81,27 @@ extern CORE_ADDR expression_context_pc;
 class innermost_block_tracker
 {
 public:
+  enum track_type
+    {
+     for_symbols = 0x1,
+     for_registers = 0x2
+    };
+
   innermost_block_tracker ()
     : m_innermost_block (NULL)
   { /* Nothing.  */ }
 
-  void reset ()
+  void reset (enum track_type t = for_symbols)
   {
+    m_type = t;
     m_innermost_block = NULL;
   }
 
-  void update (const struct block *b);
+  void update (const struct block *b, track_type t);
 
   void update (const struct block_symbol &bs)
   {
-    update (bs.block);
+    update (bs.block, for_symbols);
   }
 
   const struct block *block () const
@@ -103,9 +110,20 @@ public:
   }
 
 private:
+  enum track_type m_type;
   const struct block *m_innermost_block;
 };
 
+/* Allow the enum for block type to be bitwise-or together.  */
+
+inline enum innermost_block_tracker::track_type operator|
+		(enum innermost_block_tracker::track_type a,
+		 enum innermost_block_tracker::track_type b)
+{
+  return static_cast<enum innermost_block_tracker::track_type>
+    (static_cast<int> (a) | static_cast<int> (b));
+}
+
 /* The innermost context required by the stack and register variables
    we've encountered so far.  This should be cleared before parsing an
    expression, and queried once the parse is complete.  */
diff --git a/gdb/testsuite/gdb.mi/basics.c b/gdb/testsuite/gdb.mi/basics.c
index 08d9ccae178..327f33c6eca 100644
--- a/gdb/testsuite/gdb.mi/basics.c
+++ b/gdb/testsuite/gdb.mi/basics.c
@@ -20,6 +20,8 @@
  *      on function calls.  Useful to test printing frames, stepping, etc.
  */
 
+unsigned long long global_zero = 0;
+
 int callee4 (void)
 {
   int A=1;
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 00000000000..413fa5c3c92
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-frame-regs.exp
@@ -0,0 +1,186 @@
+# Copyright 2018 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$" {
+	    unresolved "get address of breakpoint $bpnum"
+	    return ""
+	}
+	timeout {
+	    unresolved "get address of breakpoint $bpnum (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_with_prefix do_floating_varobj_test {} {
+    global srcfile
+    global hex
+    global expect_out
+
+    gdb_exit
+    if {[mi_gdb_start]} then {
+	fail "couldn't start gdb"
+	return
+    }
+
+    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 in callee$i"
+
+	# 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 { return }
+
+	# Check that the addresses are the same.
+	gdb_assert [expr $bpaddr == $pcval] "\$pc equals address of breakpoint in callee$i"
+    }
+}
+
+# Test that fixed varobjs representing $pc in different stack frames
+# will provide the correct value via -var-update after the program
+# counter changes (without substantially changing the stack).
+
+proc_with_prefix do_fixed_varobj_test {} {
+    global srcfile
+    global hex
+
+    gdb_exit
+    if {[mi_gdb_start]} then {
+	fail "couldn't start gdb"
+	return
+    }
+
+    mi_run_to_main
+
+    # Run to the function 'callee3' so we have several frames.
+    mi_create_breakpoint "basics.c:callee3" \
+	"insert breakpoint at basics.c:callee3" \
+	-number 2 -func callee3 -file ".*basics.c"
+
+    mi_execute_to "exec-continue" "breakpoint-hit" \
+	"callee3" ".*" ".*${srcfile}" ".*" \
+	{ "" "disp=\"keep\"" } "breakpoint hit in callee3"
+
+    # At the breakpoint in callee3 there are 4 frames.
+    #
+    # Create some varobj based on $pc in all frames.  When we single
+    # step we expect the varobj for frame 0 to change, while the
+    # varobj for all other frames should be unchanged.
+    #
+    # Track in FIRST_UNCHANGING_VARNUM the number of the first varobj
+    # that is not in frame 0, varobj with a lower number we expect to
+    # change, while this and later varobj should not change.
+    #
+    # Track the number of the next varobj to be created in VARNUM.
+    set first_unchanging_varnum 0
+    set varnum 1
+
+    for {set i 0} {$i < 4} {incr i} {
+
+	if { $i == 1 } then { set first_unchanging_varnum $varnum }
+
+	mi_gdb_test "-var-create --thread 1 --frame $i - \* \$pc" \
+	    "\\^done,.*value=\"$hex.*" \
+	    "create varobj for \$pc in frame $i"
+	incr varnum
+
+	mi_gdb_test "-var-create --thread 1 --frame $i - \* \"global_zero + \$pc\"" \
+	    "\\^done,.*value=\"$hex.*" \
+	    "create varobj for 'global_zero + \$pc' in frame $i"
+	incr varnum
+    }
+
+    # Step one instruction to change the program counter.
+    mi_execute_to "exec-next-instruction" "end-stepping-range" \
+	"callee3" ".*" ".*${srcfile}" ".*" "" \
+	"next instruction in callee3"
+
+    # Check that -var-update reports that the values are changed for
+    # varobj in frame 0.
+    for {set i 1} {$i < $first_unchanging_varnum} {incr i} {
+	mi_gdb_test "-var-update 1 var$i" \
+	    "\\^done,(changelist=\\\[\{name=\"var$i\"\[^\\\]\]+\\\])" \
+	    "varobj var$i has changed"
+    }
+
+    # Check that -var-update reports that the values are unchanged for
+    # varobj in frames other than 0.
+    for {set i $first_unchanging_varnum} {$i < $varnum} {incr i} {
+	mi_gdb_test "-var-update 1 var$i" \
+	    "\\^done,(changelist=\\\[\\\])" \
+	    "varobj var$i has not changed"
+    }
+}
+
+do_fixed_varobj_test
+do_floating_varobj_test
diff --git a/gdb/testsuite/gdb.mi/mi-var-create-rtti.exp b/gdb/testsuite/gdb.mi/mi-var-create-rtti.exp
index b61c495ab41..9ea5784bcad 100644
--- a/gdb/testsuite/gdb.mi/mi-var-create-rtti.exp
+++ b/gdb/testsuite/gdb.mi/mi-var-create-rtti.exp
@@ -49,6 +49,9 @@ mi_gdb_test "-gdb-set print object on" ".*"
 # We use a explicit cast to (void *) as that is the
 # type that caused the bug this testcase is testing for.
 mi_gdb_test "-var-create sp1 * ((void*)\$sp)" \
-	    "\\^done,name=\"sp1\",numchild=\"0\",value=\"$hex\",type=\"void \\*\",has_more=\"0\"" \
+	    "\\^done,name=\"sp1\",numchild=\"0\",value=\"$hex\",type=\"void \\*\",thread-id=\"$decimal\",has_more=\"0\"" \
 	    "-var-create sp1 * \$sp"
+mi_gdb_test "-var-create sp2 @ ((void*)\$sp)" \
+	    "\\^done,name=\"sp2\",numchild=\"0\",value=\"$hex\",type=\"void \\*\",thread-id=\"$decimal\",has_more=\"0\"" \
+	    "-var-create sp2 @ \$sp"
 gdb_exit
diff --git a/gdb/varobj.c b/gdb/varobj.c
index 20dd09bd585..586bf5fc53b 100644
--- a/gdb/varobj.c
+++ b/gdb/varobj.c
@@ -311,7 +311,8 @@ varobj_create (const char *objname,
 	}
 
       p = expression;
-      innermost_block.reset ();
+      innermost_block.reset (innermost_block_tracker::for_symbols
+			     | innermost_block_tracker::for_registers);
       /* Wrap the call to parse expression, so we can 
          return a sensible error.  */
       TRY
-- 
2.14.3