Re: [open-cobol-list] Help understanding this behaviour

[Wim Niemans]

Well, Brian, there are ways to circumvent.
Occasionally I get the following error when testing my Cobol programs (not in 
openCobol):

runtime error: linkage item is smaller than passed item.

and, to my humble opinion, that is the way to go.

Wim



Op 3 sep. 2013, om 08:50 heeft Brian Tiffin het volgende geschreven:

> Advanced features to the rescue.
> 
> Wim; it isn't a bug.  It's the way of stack frames and the flexibility
> of CALL in the C ABI landscape.  Sadly, (kinda) there is no protection
> on sizes at runtime, unless coded for.  One I used to use was passing
> a length, another (when calling C) is to traverse the cob_module
> parameter space.  I still need to write up a cob_field article.  Lots
> of power when accessing cob_field from C.
> 
> There are pure COBOL ways though.  Patrick;
> 
> Try ANY LENGTH on your (incoming) linkage section.  For example
> 
>      *> Tectonics: cobc -x anylen.cob
>      *> *********************************************
>       identification division.
>       program-id. anylen.
> 
>       data division.
>       working-storage section.
>       01 some-string pic x(40) value "testing 1 2 3".
> 
>      *> *********************************************
>       procedure division.
>       call "subprogram" using some-string end-call
>       call "subprogram" using "test" end-call
>       goback.
>       end program anylen.
> 
>      *> *********************************************
>       identification division.
>       program-id. subprogram.
> 
>       data division.
>       linkage section.
>       01 some-string pic x any length.
> 
>       procedure division using some-string.
>       display
>           function length(some-string) ": #" some-string "#"
>       end-display
>       goback.
>       end program subprogram.
> 
> $ cobc -x anylen.cob
> $ ./anylen
> 00000040: #testing 1 2 3                           #
> 00000004: #test#
> 
> Cheers,
> Brian
> 
> On 9/2/13, Wim Niemans <address@hidden> wrote:
>> 
>> To me, this looks like a serious bug in the compiler, because it should
>> perform a length check.
>> When this string is longer, there seem to be no problem and I guess
>> everybody will understand that and refer to the distinct picture clauses.
>> When this string is shorter, however, Cobol should definite issue a error or
>> warning, because it otherwise facilitates a security leak.
>> The only defense that can be used is the mismatch of BY VALUE / BY REFERENCE
>> in the the caller and the callee.
>> 
>> Wim
>> 
>> 
>> 
>> Op 2 sep. 2013, om 05:09 heeft Patrick het volgende geschreven:
>> 
>>> Hi Charles, Hello Paul, Hi Michael
>>> 
>>> This all makes sense now. The "problem" is actually on the receiving end
>>> where a sort of buffer overflow occurs when the additional memory
>>> locations are read due to the mismatched values.
>>> 
>>> I suppose in production code, it's not very often that someone would
>>> just want to send a string in quotes only anyways. I am probably getting
>>> tripped up with quick mock up code.
>>> 
>>> This information will help a lot, getting used to the PIC based type
>>> system takes a bit of time but I think I am well on my way now.
>>> 
>>> Have a great night guys !
>>> 
>>> -Patrick
>>> 
>>> 
>>> 
>>> 
>>> 
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>> 
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