Re: i386.record.floating.point.patch : with more testing and assurity

[Michael Snyder <msnyder at vmware dot com>]

paawan oza wrote:
> Hi, 
> Thank you very much for your elaborated reply.
> I will integrate the test example with test suite by next week-end.
> And, also take of all yours and Hui's formatting comments.
> I will come up with the final up to date patch with integrated test-suite.
> Thank you again for your response. : )
> I start working towards it.
> Regards,
> Oza.

Excellent.  Now let's talk about what the test should test.

I don't think it is necessary to test each individual instruction
(unless you really want to).  We don't usually go to that extreme.

What we want to establish is "does the patch do what it's intended
to do", so let's make a statement about what it's intended to do.
You correct me if I'm wrong, but in my impression, it can be summed
up as: preserve and restore the state of the standard Intel floating
point unit during record and replay".

So you just need to test that the FP machine state is preserved,
and that when we go backwards, the state is restored to what it
was before.  I think that means mainly the '387' registers, or
the state that is displayed when we say "info float".

To help you get started, I've attached a simple gdb test that
checks to see if we can save and restore one register ('st0').
This will show you in general how it is done, and if you want
to, you can use it as a starting point, and add tests for the
rest of the registers.

The subroutines that we use, such as "gdb_test", are mostly
defined in gdb/testsuite/lib/gdb.exp, if you need to look at
them.  There's some documentation in the comments, and also
in gdb/doc/gdbint.texinfo.







/* Reverse debugging of floating point registers.

   Copyright 2009, Free Software Foundation, Inc.

   This file is part of GDB.

   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 main (void)
{
  int i = 0;	/* BEGIN I387-FLOAT-REVERSE */

  asm ("fldz");	/* test st0 register */
  asm ("fld1");
  asm ("nop");

  return i;	/* END I387-FLOAT-REVERSE */
}

# Copyright 2009 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/>.

# This file is part of the gdb testsuite.

if $tracelevel {
    strace $tracelevel
}

set prms_id 0
set bug_id 0

if ![istarget "i?86-*linux*"] then {
    verbose "Skipping i387 reverse float tests."
    return
}

set testfile "i387-float-reverse"
set srcfile ${testfile}.c
set binfile ${objdir}/${subdir}/${testfile}

# some targets have leading underscores on assembly symbols.
# TODO: detect this automatically
set additional_flags ""
if [istarget "i?86-*-cygwin*"] then {
  set additional_flags "additional_flags=-DSYMBOL_PREFIX=\"_\""
}

if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable [list debug $additional_flags]] != "" } {
    untested i387-float-reverse
    return -1
}

# Get things started.

gdb_exit
gdb_start
gdb_reinitialize_dir $srcdir/$subdir
gdb_load ${binfile}
runto main

# Record to end of main

set location [gdb_get_line_number "END I387-FLOAT-REVERSE"]
gdb_test "record" "" "Turn on process record"
gdb_test "until $location" ".*/$srcfile:$location.*" \
    "record to end of main"

# Now rewind to beginning so we can begin testing.

set location [gdb_get_line_number "BEGIN I387-FLOAT-REVERSE"]
gdb_test "set exec-dir reverse" "" "set reverse direction"
gdb_test "until $location" ".*/$srcfile:$location.*" \
    "rewind to beginning of main"
gdb_test "set exec-dir forward" "" "set forward direction"

# Test st0 register

set location [gdb_get_line_number "test st0 register"]
gdb_test "until $location" ".*/$srcfile:$location.*asm.*fldz.*" \
    "begin test st0"
gdb_test "stepi" "asm.*fld1.*"            "set st0 == 0"
gdb_test "info register st0" "st0 *0\t.*" "verify st0 == 0"
gdb_test "stepi" "asm.*nop.*"             "set st0 == 1"
gdb_test "info register st0" "st0 *1\t.*" "verify st0 == 1"

# Now step backward, and check that st0 value reverts to zero.

gdb_test "reverse-stepi" "asm.*fld1.*"    "undo set st0 == 1"
gdb_test "info register st0" "st0 *0\t.*" "verify st0 == 0 again"