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

Yao Qi
2012-08-17T02:21:23Z

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