[PATCH 4/4] rtems-debugger-target.c: Fix Coverity Dereference before null check

[Gedare Bloom]

On Thu, Feb 11, 2021 at 2:33 PM Joel Sherrill <joel at rtems.org> wrote:
>
>
>
> On Thu, Feb 11, 2021 at 3:29 PM Chris Johns <chrisj at rtems.org> wrote:
>>
>> On 12/2/21 8:16 am, Gedare Bloom wrote:
>> > On Thu, Feb 11, 2021 at 2:00 PM Chris Johns <chrisj at rtems.org> wrote:
>> >>
>> >> On 12/2/21 7:27 am, Ryan Long wrote:
>> >>> Fixes CID #1468682 where target is dereferenced before it has been
>> >>> checked as to whether it is null or not in the
>> >>> rtems_debugger_target_swbreak_control function.
>> >>> ---
>> >>>  cpukit/libdebugger/rtems-debugger-target.c | 5 +++--
>> >>>  1 file changed, 3 insertions(+), 2 deletions(-)
>> >>>
>> >>> diff --git a/cpukit/libdebugger/rtems-debugger-target.c b/cpukit/libdebugger/rtems-debugger-target.c
>> >>> index e495170..3726a6c 100644
>> >>> --- a/cpukit/libdebugger/rtems-debugger-target.c
>> >>> +++ b/cpukit/libdebugger/rtems-debugger-target.c
>> >>> @@ -171,17 +171,18 @@ int
>> >>>  rtems_debugger_target_swbreak_control(bool insert, DB_UINT addr, DB_UINT kind)
>> >>>  {
>> >>>    rtems_debugger_target*         target = rtems_debugger->target;
>> >>> -  rtems_debugger_target_swbreak* swbreaks = target->swbreaks.block;
>> >>>    size_t                         swbreak_size;
>> >>>    uint8_t*                       loc = (void*) addr;
>> >>>    size_t                         i;
>> >>>    int                            r;
>> >>>
>> >>> -  if (target == NULL || swbreaks == NULL || kind != target->breakpoint_size) {
>> >>> +  if (target == NULL || target->swbreaks.block == NULL ||
>> >>> +      kind != target->breakpoint_size) {
>> >>>      errno = EIO;
>> >>>      return -1;
>> >>>    }
>> >>>
>> >>> +  rtems_debugger_target_swbreak* swbreaks = target->swbreaks.block;
>> >>
>> >> The debug server does not declare local vars in the body of functions. I would
>> >> prefer the this code base stays that way if that is OK?
>> >>
>> > Good catch. This is a holdover from ANSI C that we should generally
>> > adhere to in RTEMS cpukit code for historical reasons.
>>
>> Yes I agree. I understand and accept this is a personal thing and I stated my
>> preference in the other post.
>
>
> No. I missed that you wanted the variable at the top of scope. I agree that
> tighter scoping is more a C++ thing than a C thing.  I was looking for something
> more complicated.
>>
>>
>> I use this feature judicially in C++ where I think it is more important to do
>> so. In C++ a variable can be declared in a number of ways and places and I feel
>> being consistent aids readability. Compilers are smart enough to figure out when
>> a variable become active and we do not need to help.
>
>
> It is nice when a temporary variable is only used inside an if or loop.
>

It is naughty when a block variable shadows a different local variable
(or a global). So there are pros/cons, as usual.

> --joel
>>
>>
>> Chris
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