Re: [RFC] Don't allow setting register in non-innermost frame

[Yao Qi <yao at codesourcery dot com>]

On 09/08/2012 12:45 AM, Jan Kratochvil wrote:
> (gdb) set variable i=20
> warning: Assigning to register in non-innermost frame.
> 
> Why?
> 
> I would find correct to print such warning for:
> 	(gdb) set $rbx=20
> There it should happen only if user has explicitly specified the register
> itself.

I checked the difference of value of register and value of variable
(saved in register), TYPE_OBJFILE_OWNED (value_type (toval)) is the
only difference between them.  IIUC, type of variable is owned by an
objfile, while type of register is not (alloc_type vs. alloc_type_arch),
so looks we can use it to differentiate values in register and values
in variables.

This new patch includes TYPE_OBJFILE_OWNED into the condition, and
adjust the NEWS entry discussed with Eli before.

-- 
Yao

gdb/testsuite:

2012-09-10  Yao Qi  <yao@codesourcery.com>

	* gdb.base/set-reg.exp: New.
	* gdb.base/set-reg.c: New.

gdb:

2012-09-10  Yao Qi  <yao@codesourcery.com>
	    Doug Evans  <dje@google.com>

	* valops.c (value_assign): Emit warning when assigning to
	registers in non-innermost frames.
	* NEWS: Mention it.
---
 gdb/NEWS                           |    3 +
 gdb/testsuite/gdb.base/set-reg.c   |   40 ++++++++++
 gdb/testsuite/gdb.base/set-reg.exp |  139 ++++++++++++++++++++++++++++++++++++
 gdb/valops.c                       |   16 ++++
 4 files changed, 198 insertions(+), 0 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/set-reg.c
 create mode 100644 gdb/testsuite/gdb.base/set-reg.exp

diff --git a/gdb/NEWS b/gdb/NEWS
index dba6937..f7476e4 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -17,6 +17,9 @@
 * The 'cd' command now defaults to using '~' (the home directory) if not
   given an argument.
 
+* GDB will display a warning when assigning to registers by CLI command
+  "set" or MI command "-var-assign" in non-innermost frames.
+
 * New configure options
 
 --enable-libmcheck/--disable-libmcheck
diff --git a/gdb/testsuite/gdb.base/set-reg.c b/gdb/testsuite/gdb.base/set-reg.c
new file mode 100644
index 0000000..03938eb
--- /dev/null
+++ b/gdb/testsuite/gdb.base/set-reg.c
@@ -0,0 +1,40 @@
+/* This test is part of GDB, the GNU debugger.
+
+   Copyright 2012 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/>.  */
+
+static int
+inner (int x)
+{
+  return x + 2;
+}
+
+static int
+middle (int x)
+{
+  return 2 * inner (x);
+}
+
+static int
+top (int x)
+{
+  return 2 * middle (x);
+}
+
+int
+main (int argc,  char **argv)
+{
+  return top (argc);
+}
diff --git a/gdb/testsuite/gdb.base/set-reg.exp b/gdb/testsuite/gdb.base/set-reg.exp
new file mode 100644
index 0000000..5ea65da
--- /dev/null
+++ b/gdb/testsuite/gdb.base/set-reg.exp
@@ -0,0 +1,139 @@
+# Copyright 2012 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/>.
+
+standard_testfile
+set executable $testfile
+
+# A value in register in previous frame.  E.g,. call-clobbered register.
+set reg_prev_frame_in_reg "unknown"
+# A (register) value in memory in previous frame.  E.g., call-saved register.
+set reg_prev_frame_in_memory "unknown"
+
+if [is_amd64_regs_target] {
+    set reg_prev_frame_in_reg "rax"
+    set reg_prev_frame_in_memory "rbp"
+} elseif [is_x86_like_target] {
+    set reg_prev_frame_in_reg "eax"
+    set reg_prev_frame_in_memory "ebp"
+} else {
+    # set reg_prev_frame_in_reg for other arch.
+}
+
+# Name of register is not set, skip the rest of test.
+if { [string equal $reg_prev_frame_in_reg "unknown"] } {
+    return
+}
+
+if { [gdb_compile $srcdir/$subdir/$srcfile $binfile executable {debug}] != "" } {
+    untested "Failed to compile"
+    return -1
+}
+
+proc set_register { register check_value } {with_test_prefix "${register} ${check_value}" {
+    global decimal
+    global gdb_prompt
+
+    set reg_val ""
+    gdb_test_multiple "p/d \$${register}" "print register ${register}" {
+	-re ".*${decimal} = ($decimal).*$gdb_prompt $" {
+	    set reg_val $expect_out(1,string)
+	}
+    }
+    if { $reg_val == "" } {
+	fail "get the value of register ${register}"
+	return
+    }
+
+    # Assign the same value to register.
+    gdb_test_no_output "set \$${register}=${reg_val}" \
+	"set register ${register} on inner frame (unchanged)"
+
+    # Assign the different value to register.
+    set reg_val [expr $reg_val + 4]
+    gdb_test_no_output "set \$${register}=${reg_val}" \
+	"set register ${register} on inner frame (changed)"
+    gdb_test "p/d \$${register}" ".*${decimal} = $reg_val.*" \
+	"register ${register} is changed"
+
+    # Restore register.
+    set reg_val [expr $reg_val - 4]
+    gdb_test_no_output "set \$${register}=${reg_val}" \
+	"set register ${register} on inner frame (restored)"
+    gdb_test "p/d \$${register}" ".*${decimal} = $reg_val.*" \
+	"register ${register} is restored"
+
+    gdb_test "up"
+
+    gdb_test_multiple "p/d \$${register}" "print register ${register}" {
+	-re ".*${decimal} = ($decimal).*$gdb_prompt $" {
+	    set reg_val $expect_out(1,string)
+	}
+    }
+    if { $reg_val == "" } {
+	fail "get the value of register ${register}"
+	return
+    }
+    # Assign the same value to register.
+    gdb_test "set \$${register}=${reg_val}" \
+	"Assigning to register in non-innermost frame.*" \
+	"set register ${register} on non-inner frame"
+
+    if { $check_value } {
+	# Assign the different value to register.
+	set reg_val [expr $reg_val + 4]
+	gdb_test "set \$${register}=${reg_val}" \
+	    "Assigning to register in non-innermost frame.*" \
+	    "set register ${register} on non-inner frame (changed)"
+	gdb_test "p/d \$${register}" ".*${decimal} = $reg_val.*" \
+	    "register ${register} is changed"
+	# Restore register.
+	set reg_val [expr $reg_val - 4]
+	gdb_test "set \$${register}=${reg_val}" \
+	    "Assigning to register in non-innermost frame.*" \
+	    "set register ${register} on non-inner frame (restored)"
+	gdb_test "p/d \$${register}" ".*${decimal} = $reg_val.*" \
+	    "register ${register} is restored"
+    }
+    gdb_test "down"
+}}
+
+# Test setting register on innermost frame and non-innermost frame.
+
+proc test_set_reg_on_frame {} {with_test_prefix "on frame" {
+    global executable
+    global reg_prev_frame_in_reg
+    global reg_prev_frame_in_memory
+    global decimal
+    global hex
+    global expect_out
+    global gdb_prompt
+
+    clean_restart $executable
+
+    if ![runto_main] {
+	return
+    }
+
+    gdb_test "break inner" "Breakpoint.*at.* file .*, line.*"
+    gdb_test "continue" "Continuing.\r\n\r\nBreakpoint.*inner.*at.*" \
+	"continue to inner"
+
+    set_register ${reg_prev_frame_in_reg} 1
+    # Change the register saved on frame may clobber the frame, and get
+    # the contents of registers in mess.  Don't check register value.
+    set_register ${reg_prev_frame_in_memory} 0
+}}
+
+test_set_reg_on_frame
diff --git a/gdb/valops.c b/gdb/valops.c
index 17696ee..7ac23e3 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -1241,6 +1241,22 @@ value_assign (struct value *toval, struct value *fromval)
      and then restore the new frame afterwards.  */
   old_frame = get_frame_id (deprecated_safe_get_selected_frame ());
 
+  /* TOVAL is a register, although VALUE_LVAL(TOVAL) may not be
+     lval_register.  A call-saved register saved in memory will have
+     'VALUE_REGNUM >= 0' but 'VALUE_LVAL == lval_memory'.  We also have to
+     avoid emitting warning when assign value to some local variables which
+     are stored in registers, TYPE_OBJFILE_OWNED helps to differentiate
+     we are assigning to a register explicitly or to a variable saved in
+     register.  */
+  if (VALUE_REGNUM (toval) >= 0 && !TYPE_OBJFILE_OWNED (type))
+    {
+      /* Figure out which frame this is in currently.  */
+      struct frame_info *frame = frame_find_by_id (VALUE_FRAME_ID (toval));
+
+      if (get_next_frame (frame) != NULL)
+	warning (_("Assigning to register in non-innermost frame."));
+    }
+
   switch (VALUE_LVAL (toval))
     {
     case lval_internalvar:
-- 
1.7.7.6