(j3.2006) Comment 2 from TS Ballot

[Bill Long]

On 9/11/12 3:07 AM, Malcolm Cohen wrote:
> This seems overly complicated, needs better wording,
>    ... do not use "allow" to make a requirement
> overly restrictive - does not allow byte-level access to larger objects,
>     e.g.
>           /* x describes an object of size eltsize bytes. */
>           unsigned char *p = x->base_addr;
>           for (i=0; i<eltsize; i++) printf(" %x",p[i]);
> not restrictive enough - does not prohibit access to storage not part of the
> described object
>     e.g.
>           /* x describes INTEGER BASE(10); X => BASE(::2) */
>           struct { int c[2]; } *p = x->base_addr;
>           printf("%d\n",p->c[1]); /* Not part of the described object. */
> incredibly overly restrictive - prohibits use of unrelated pointers
>    e.g.
>           /* x describes INTEGER a(100), y describes a(10::2) */
>           int *p1 = x->base_addr, *p2 => y->base_addr;
>           printf("%d\n",*(p1+10)); /* within Y but cannot be obtained from
> CFI_address on Y */
>
> Maybe something like
> "If (blah), a pointer derived from the base_addr of that descriptor shall not be
> used to access memory that is not part of the object described by the
> descriptor."


Better.  I'm still a bit concerned that "derived from" is too vague. 
How about "..., a pointer computed as an offset from the base_addr of 
that descriptor...".   This wording corresponds more directly to what 
the programmer would actually be writing.

Cheers,
Bill


>
> Like Bill, I thought we already discussed this and had some words, but I did not
> spend any time looking for them.
>
> Cheers,
>
> -----Original Message-----
> From: Bader, Reinhold
> Date: ?????? 24???9???11??? 6:47
> To: fortran standards email list for J3
> Cc: Bill Long
> Subject: Re: (j3.2006) Comment 2 from TS Ballot
>
> Answering my own response ...
>
> If we have these additional words, we might as well drop references to
> pointer arithmetic:
>
> "If a formal parameter that is a pointer to CFI_cdesc_t corresponds to a dummy
> argument in an interoperable procedure interface, indirection on a
> pointer that is a valid address within the C object starting at base_addr
> is allowed if and only if the value of that pointer can be obtained
> by applying the function CFI_address (8.3.5.2) to the object or a subobject of
> it."
>
>
>>
>> "If a formal parameter that is a pointer to CFI_cdesc_t corresponds to a dummy
>> argument in an interoperable procedure interface, indirection on a
>> pointer derived from its base_addr member by pointer arithmetic that is
>> a valid address within the C object starting at base_addr
>>   is allowed if and only if the value of that pointer can be obtained
>> by applying the function CFI_address (8.3.5.2) to the object or a subobject of
>> it."
>>
>
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-- 
Bill Long                                           longb at cray.com
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