Re: [PATCH] Fix PR gdb/16999

[Patrick Palka <patrick at parcs dot ath dot cx>]

On Thu, May 14, 2015 at 6:16 AM, Pedro Alves <palves@redhat.com> wrote:
> On 05/13/2015 11:17 PM, Patrick Palka wrote:
>> When GDB reads a nonsensical value for the HISTSIZE environment variable
>> variable, i.e. one that is non-numeric or negative, GDB then sets its
>> history size to 0.  This behavior is contrary to that of bash, which
>> defaults the history size to unlimited in such cases.
>>
>> This patch makes the behavior of invalid HISTSIZE match that of bash.
>> When we encounter an invalid HISTSIZE we now set the history size to
>> unlimited instead of 0.
>>
>> gdb/ChangeLog:
>>
>>       PR gdb/16999
>>       * top.c (init_history): For invalid HISTSIZE, set history size
>>       to unlimited.
>>
>> gdb/testsuite/ChangeLog:
>>
>>       PR gdb/16999
>>       * gdb.base/histsize-history.exp: New test.
>> ---
>>  gdb/testsuite/gdb.base/histsize-history.exp | 54 +++++++++++++++++++++++++++++
>>  gdb/top.c                                   | 16 ++++-----
>>  2 files changed, 62 insertions(+), 8 deletions(-)
>>  create mode 100644 gdb/testsuite/gdb.base/histsize-history.exp
>>
>> diff --git a/gdb/testsuite/gdb.base/histsize-history.exp b/gdb/testsuite/gdb.base/histsize-history.exp
>> new file mode 100644
>> index 0000000..b7b13cf
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.base/histsize-history.exp
>> @@ -0,0 +1,54 @@
>> +# Copyright 2015 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.
>> +
>> +# Test the setting of "history size" via the HISTSIZE environment variable
>> +
>> +
>> +# Check that the history size is properly set to SIZE when env(HISTSIZE) is set
>> +# to HISTSIZE.
>> +
>> +proc test_histsize_history_setting { histsize size } {
>> +    global env
>> +
>> +    if [info exists env(HISTSIZE)] {
>> +        set old_histsize $env(HISTSIZE)
>> +    }
>> +    set env(HISTSIZE) $histsize
>> +
>> +    gdb_exit
>> +    gdb_start
>> +
>> +    gdb_test "show history size" "The size of the command history is $size."
>> +
>> +    if { $size == "0" } {
>> +        gdb_test_no_output "show commands"
>> +    } elseif { $size != "1" } {
>> +        gdb_test "show commands" "    .  show history size\r\n    .  show commands"
>> +    }
>> +
>> +    if [info exists old_histsize] {
>> +        set env(HISTSIZE) $old_histsize
>> +    } else {
>> +        unset env(HISTSIZE)
>> +    }
>> +}
>> +
>> +test_histsize_history_setting "0" "0"
>> +test_histsize_history_setting "20" "20"
>> +test_histsize_history_setting "-5" "unlimited"
>> +test_histsize_history_setting "not_an_integer" "unlimited"
>> +test_histsize_history_setting "10zab" "unlimited"
>> diff --git a/gdb/top.c b/gdb/top.c
>> index 74e1e07..00fee8d 100644
>> --- a/gdb/top.c
>> +++ b/gdb/top.c
>> @@ -1684,15 +1684,15 @@ init_history (void)
>>    if (tmpenv)
>>      {
>>        int var;
>> +      char *endptr;
>>
>> -      var = atoi (tmpenv);
>> -      if (var < 0)
>> -     {
>> -       /* Prefer ending up with no history rather than overflowing
>> -          readline's history interface, which uses signed 'int'
>> -          everywhere.  */
>> -       var = 0;
>> -     }
>> +      var = strtol (tmpenv, &endptr, 10);
>> +
>> +      /* For the sake of consistency with bash, if HISTSIZE is
>> +      non-numeric or if HISTSIZE is negative then set our history
>> +      size to unlimited.  */
>> +      if (*endptr != '\0' || var < 0)
>> +     var = -1;
>
> Hmm, looking at the master branch (Bash-4.3 patch 33) in:
>   http://git.savannah.gnu.org/cgit/bash.git
>
> This seems to be where bash implements this:
>
> #if defined (HISTORY)
> /* What to do after the HISTSIZE or HISTFILESIZE variables change.
>    If there is a value for this HISTSIZE (and it is numeric), then stifle
>    the history.  Otherwise, if there is NO value for this variable,
>                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>    unstifle the history.  If name is HISTFILESIZE, and its value is
>    ^^^^^^^^^^^^^^^^^^^^
>    numeric, truncate the history file to hold no more than that many
>    lines. */
> void
> sv_histsize (name)
>      char *name;
> {
>   char *temp;
>   intmax_t num;
>   int hmax;
>
>   temp = get_string_value (name);
>
>   if (temp && *temp)
>     {
>       if (legal_number (temp, &num))
>         {
>           hmax = num;
>           if (hmax < 0 && name[4] == 'S')
>             unstifle_history ();        /* unstifle history if HISTSIZE < 0 */
>           else if (name[4] == 'S')
>             {
>               stifle_history (hmax);
>               hmax = where_history ();
>               if (history_lines_this_session > hmax)
>                 history_lines_this_session = hmax;
>             }
>           else if (hmax >= 0)   /* truncate HISTFILE if HISTFILESIZE >= 0 */
>             {
>               history_truncate_file (get_string_value ("HISTFILE"), hmax);
>               if (hmax <= history_lines_in_file)
>                 history_lines_in_file = hmax;
>             }
>         }
>     }
>   else if (name[4] == 'S')
>     unstifle_history ();
> }
>
>
> Note the comment I underlined above.
>
>
> If I'm reading right, stripping out all the HISTFILESIZE handling
> and then removing dead code, we get:
>
> void
> sv_histsize (char * name)
> {
>   char *temp;
>   intmax_t num;
>   int hmax;
>
>   temp = get_string_value (name);
>
>   if (temp && *temp)
>     {
>       if (legal_number (temp, &num))
>         {
>           hmax = num;
>           if (hmax < 0)
>             unstifle_history ();        /* unstifle history if HISTSIZE < 0 */
>           else
>             stifle_history (hmax);
>         }
>     }
>   else
>     unstifle_history ();
> }
>
> Note:
>
>  #1 - if HISTSIZE is non-numeric nothing happens.  I think that means
>       bash ends up with the default history size.
>
>  #2 - if HISTSIZE is set to the empty string, bash ends up
>       with unlimited history size.
>
> It seems to me that your patch handles both of these differently.
>
> #2 appears consistent with what is suggested here:
>
>   http://stackoverflow.com/questions/9457233/unlimited-bash-history
>
> "Set HISTSIZE and HISTFILESIZE to an empty string:
>
>  HISTSIZE= HISTFILESIZE=
>
>  In bash 4.3 and later you can also use HISTSIZE=-1 HISTFILESIZE=-1:
> "

When HISTSIZE is the empty string, I think we invoke UB.  I'm not sure atoi()

I was basing this patch off of the behavior of HISTFILESIZE, not
HISTSIZE.  This is because the behavior of HISTFILESIZE is more
specified than that of HISTSIZE.  According to the documentation for
HISTFILESIZE:

    Non-numeric values and numeric values less than zero inhibit
truncation.  The shell sets the default value to the value of HISTSIZE
after reading any startup files. ... If HISTFILESIZE is unset, or set
to null, a non-numeric value, or a numeric value less than zero, the
history file is not truncated.

Whereas for HISTSIZE, the documentation just says:

    If the value is 0, commands are not saved in the history list.
Numeric values less than zero result in every command being saved on
the history list (there is no limit).

bash does not explicitly document what happens if HISTSIZE is null or
non-numeric.  And because HISTSIZE determines both GDB's in-memory and
in-file history size (we don't respond to HISTFILESIZE) I think it's
not so bad to base our behavior of HISTSIZE handling off of bash's
HISTFILESIZE handling.   (Though I should've mentioned this in the
patch.)

But unless GDB responds to both HISTSIZE and HISTFILESIZE I suppose we
will never be truly consistent with bash since apparently both of
these variables have different behaviors under edge cases.

So should we anyway match the behavior of bash's HISTSIZE?