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

[Yao Qi <yao at codesourcery dot com>]

On 09/05/2012 06:36 AM, dje@google.com wrote:
>   >
>   > gdb/testsuite:
>   >
>   > 2012-08-29  Yao Qi  <yao@codesourcery.com>
>   >
>   > 	* gdb.base/set-reg.exp: New.
>   > 	* gdb.base/set-reg.c: New.
>   >
>   > gdb:
>   >
>   > 2012-08-29  Yao Qi  <yao@codesourcery.com>
>   >
>   > 	* valops.c (value_assign): Emit warning if get_next_frame returns
>   > 	non-NULL.
> 
> The description here is insufficient.
> I look at it and think "Eh?" (e.g. it says nothing about register values).
> The point is that we're warning about assigning to registers in non-innermost
> frames, so say that.
> 
> 	* valops.c (value_assign): Emit warning when assigning to registers
> 	in non-innermost frames.
> 

OK.

> I think this is NEWS-worthy.
> 

I add a NEWS entry.


>   > +
>   > +int
>   > +inner (int x)
>   > +{
>   > +  return x + 2;
>   > +}
>   > +
>   > +static short
> 
> The mixture short vs int, extern vs static, is excessive.
> How about make inner,middle,top all "static int" ?
> 

Sure.  The set-reg.c is copied from other c file in test suite, and I
 didn't change it much.


>   > +# A value in register in previous frame.
> 
> -->
> # A value in register in previous frame.  E.g,. call-clobbered register.
> 
>   > +set reg_prev_frame_in_reg "unknown"
>   > +# A value in memory in previous frame.
> 
> -->
> # A (register) value in memory in previous frame.  E.g., call-saved register.
> 

Fixed.

>   > +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.
> 
> Remove extra blank line before }.
> 

This blank line is removed.

>   > +
>   > +}
>   > +
>   > +# Test setting register on innermost frame and non-innermost frame.
>   > +
>   > +proc test_set_reg_on_frame {} {with_test_prefix "on frame" {
> 
> Does prefix "on frame" provide anything useful here?
> [IOW, what would we lose if we remove it?]
> 

At this moment, it doesn't.  However, I plan to add other tests in 
set-reg.exp in the future, so I add this prefix to avoid duplicated 
result.

>   > +    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
> 
> We don't put much effort into caring about return values when, e.g.,
> runto_main fails (throughout the testsuite).
> But here, how about just "return".
> 

OK.

>   > +    }
>   > +
>   > +    # Name of register is not set, skip the rest of test.
>   > +    if { [string equal $reg_prev_frame_in_reg "unknown"] } {
>   > +	return 1
>   > +    }
> 
> Why have this exit test here?  Seems pretty inefficient.
> How about doing the test in the caller (top level)?
> [And even skip the compilation step if there's no point.]
> 

This check can be moved to the very beginning of test, even before compilation step.

>   > +
>   > +    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)
>   > +	}
>   > +    }
> 
> If reg_val is "" at this point the test is in trouble.
> Better watch for it and handle it appropriately.
> 

OK, it is handled in new version.

> Plus you assign reg_val to both the in_reg and in_memory regs.
> Given that one is rax and the other is rbp, that seems awkward.
> 
> One thing that's missing is that if we're going to test assigning
> to registers, IWBN to test that the assignment worked.
> If we assign the value it already had, the assignment may have failed
> but we wouldn't (as easily) find out.
> 

The original intention of this test is to verify that an error or
 warning is emitted when changing register on non-inner most frame.  So 
it doesn't cover 'checking register content is really changed', as you 
pointed out.  I am fine to add them.  Note that modifying 'ebp' on 
non-inner most frame will get registers in mess, so I don't check the 
contents of 'ebp'.

>   > +
>   > +    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_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"
>   > +    }
>   > +
>   > +    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"
>   > +}}
>   > +
>   > +test_set_reg_on_frame
>   > diff --git a/gdb/valops.c b/gdb/valops.c
>   > index 17696ee..cb84c87 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.  */
> 
> IWBN to expand on this a bit.
> 
> E.g.,
> "A call-saved register saved in memory will have VALUE_REGNUM >= 0
> but VALUE_LVAL == lval_memory."
> Or some such.
> 

Copied your sentence to the comment directly :).

>   > +  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)
>   > +	warning (_("Frame in which this value is assigned to is"
>   > +		   " not innermost."));
> 
> IWBN to mention that this warning explicitly applies to registers.
> Maybe something like:
> "Assigning to register in non-innermost frame."
> 

That is better.

-- 
Yao

gdb/testsuite:

2012-09-07  Yao Qi  <yao@codesourcery.com>

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

gdb:

2012-09-07  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                       |   12 +++
 4 files changed, 194 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..5f1eb67 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 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..ae19601 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.  A call-saved register saved in memory will have
+     'VALUE_REGNUM >= 0' but 'VALUE_LVAL == lval_memory'.  */
+  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)
+	warning (_("Assigning to register in non-innermost frame."));
+    }
+
   switch (VALUE_LVAL (toval))
     {
     case lval_internalvar:
-- 
1.7.7.6