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Re: [patch libstdc++]: Fix LLP64 pointer-size issues for cxxabi, eh_alloc, and hash_bytes


2012/12/21 Gabriel Dos Reis <gdr@integrable-solutions.net>:
> On Fri, Dec 21, 2012 at 3:48 AM, Kai Tietz <ktietz70@googlemail.com> wrote:
>> 2012/12/21 Paolo Carlini <paolo.carlini@oracle.com>:
>>> On 12/21/2012 10:36 AM, Kai Tietz wrote:
>>>>
>>>> well, issue isn't that 'long' is always 'ptrdiff_t'.
>>>
>>> But then, if we just change the type without paying attention to size (and
>>> alignment) aren't we looking for BIG ABI trouble?!?
>>
>> Huh?  We have ABI-trouble due long is  too small to hold a
>> pointer-diff for llp64.  Intended is here 'pointer-size' AFAICS in
>> code, but with wrong assumption that a 'long' is always long enough.
>>
>>  Btw I just checked all targets we have right now in gcc.  The type
>> ptrdiff_t is always either 'long', or 'int' (ilp32, lp64), and 'long
>> long' for LLP64.  Means ptrdiff_t gets always equal (or bigger) to
>> biggest pointer-size for target (AFAICS).
>>
>> Kai
>
> We must write the codes so that their intents are clear, without
> requiring lot of reverse engineering every time one looks at them.  If we
> intend offset, then clearly ptrdiff_t is the first choice.  Solid
> reasons must be provided why it can't be ptrdiff_t and such
> reasons must be part of the code as comments explaining why
> the obvious thing should be discounted.
>
> - Gaby

Agreed that we are using at some place too complex logic to avoid
standard-types we already have ...
We need to modify for cxxabi.h header-change also cp/rtti.c, as here
the 'long' type-assumption is done, too.  instead of using
integer_type[itk_long/itk_long_long] there we then have to use instead
ptrdiff_type_node.  And this is for some targets a possible ABI-change
due type_info-record might change size ... for 4.9 this change looks
suitable to me, but for 4.8 we should simply check for now for
itk_long/itk_long_long here (as done by other patch I've sent).

Kai


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