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

[Yao Qi <yao at codesourcery dot com>]

Hi,
When playing with 'set $reg=0xXXX', I am thinking about the expected
behaviour of setting register when the frame is not innermost.  Current
GDB will invalidate regcaches and reinit frache_caches for any register
changes (on innermost and non-innermost frame).  However, the semantics
of 'setting register on non-innermost frame' is tricky.  On innermost
frame, 'setting register' means writing something to register in cpu,
while on non-innermost frame, it means writing something to either
real register (regcache) or memory (frame).  On the other head, I am
trying to figure out a situation that user has to set register on
non-innermost frame.  Why does this user have to do that?

Literally, IMO, 'set $reg=0xXXXX' means 'setting the cpu register $reg
to value 0xXXX', which is simple and clear.  I propose to restrict
setting register in innermost frame only.  WDYT?

Regression tested on x86_64-linux.  Surprisingly, we don't have a test
case for 'set register', so I add one.  In the future, I plan to add
more tests here for 'set register', such as 'set some bits of a register'
and 'set multiple registers in one time', to cover the different
paths in value_assign for 'lval_register'.

gdb:
	* valops.c (value_assign): Emit error if get_next_frame returns
	non-NULL.

gdb/testsuite:

 	* gdb.base/set-reg.exp: New.
---
 gdb/testsuite/gdb.base/set-reg.c   |   40 +++++++++++++
 gdb/testsuite/gdb.base/set-reg.exp |  108 ++++++++++++++++++++++++++++++++++++
 gdb/valops.c                       |   12 ++++
 3 files changed, 160 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/testsuite/gdb.base/set-reg.c b/gdb/testsuite/gdb.base/set-reg.c
new file mode 100644
index 0000000..7ce350d
--- /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/>.  */
+
+int
+inner (int x)
+{
+  return x + 2;
+}
+
+static short
+middle (int x)
+{
+  return 2 * inner (x);
+}
+
+short
+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..abe7764
--- /dev/null
+++ b/gdb/testsuite/gdb.base/set-reg.exp
@@ -0,0 +1,108 @@
+# 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
+
+if { [gdb_compile $srcdir/$subdir/$srcfile $binfile executable {debug}] != "" } {
+    untested "Failed to compile"
+    return -1
+}
+
+# A value in register in previous frame.
+set reg_prev_frame_in_reg "unknown"
+# A value in memory in previous frame.
+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.
+
+}
+
+# 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 -1
+    }
+
+    # Name of register is not set, skip the rest of test.
+    if { [string equal $reg_prev_frame_in_reg "unknown"] } {
+	return 1
+    }
+
+    gdb_test "break inner" "Breakpoint.*at.* file .*, line.*"
+    gdb_test "continue" "Continuing.\r\n\r\nBreakpoint.*inner.*at.*" \
+	"continue to inner"
+
+    gdb_test_sequence "bt" "bt before setting reg" {
+	"\[\r\n\]#0 .* inner \\(x=1\\) at "
+	"\[\r\n\]#1 .* middle \\(x=1\\) at "
+	"\[\r\n\]#2 .* top \\(x=1\\) at "
+	"\[\r\n\]#3 .* main \\(.*\\) at"
+    }
+
+    set reg_val ""
+    gdb_test_multiple "p/x \$${reg_prev_frame_in_reg}" "print register ${reg_prev_frame_in_reg}" {
+	-re ".*${decimal} = ($hex).*$gdb_prompt $" {
+	    set reg_val $expect_out(1,string)
+	}
+    }
+
+    gdb_test_no_output "set \$${reg_prev_frame_in_reg}=${reg_val}" \
+	"set register ${reg_prev_frame_in_reg} on inner frame"
+
+    # Stack is unchanged.
+    gdb_test_sequence "bt" "bt after setting reg" {
+	"\[\r\n\]#0 .* inner \\(x=1\\) at "
+	"\[\r\n\]#1 .* middle \\(x=1\\) at "
+	"\[\r\n\]#2 .* top \\(x=1\\) at "
+	"\[\r\n\]#3 .* main \\(.*\\) at"
+    }
+
+    gdb_test "up"
+    gdb_test "set \$${reg_prev_frame_in_reg}=${reg_val}" \
+	"Frame in which this value is assigned to is not innermost.*" \
+	"set register ${reg_prev_frame_in_reg} on non-inner frame"
+
+    gdb_test "set \$${reg_prev_frame_in_memory}=${reg_val}" \
+	"Frame in which this value is assigned to is not innermost.*" \
+	"set register ${reg_prev_frame_in_memory} on non-inner frame"
+
+   gdb_test_sequence "bt" "bt after up" {
+	"\[\r\n\]#0 .* inner \\(x=1\\) at "
+	"\[\r\n\]#1 .* middle \\(x=1\\) at "
+	"\[\r\n\]#2 .* top \\(x=1\\) at "
+	"\[\r\n\]#3 .* main \\(.*\\) at"
+    }
+}}
+
+test_set_reg_on_frame
diff --git a/gdb/valops.c b/gdb/valops.c
index 8167cd4..14540b8 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -1241,6 +1241,18 @@ 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.  */
+  if (VALUE_REGNUM (toval) >= 0)
+    {
+      /* 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)
+	error (_("Frame in which this value is assigned to is"
+		 " not innermost."));
+    }
+
   switch (VALUE_LVAL (toval))
     {
     case lval_internalvar:
-- 
1.7.7.6