Re: Memory Manager DLL Validation


"Pierre le Riche" <pleriche@xxxxxxxxxxx> wrote in message
news:4264ca54@xxxxxxxxxxxxxxxxxxxxxxxxx
> Hi John,
>
>> I thought the rule finally agreed on was that it is allowed to write but
>> NOT modify any data beyond the last used character.
>
> How do you guarantee that the extra bytes you're writing is not modifying
> the data beyond the last used character? In a multi-threaded environment
> those bytes may change at any time, and unless you're going to resort to
> using "lock cmpxchg x, y" (which would kill performance) you'll never be
> safe.
>
> I propose that this rule be scrapped since it is not practical.
>
> IMO reading past the end is fine, but writing is not acceptable. Has
> anybody asked Borland's opinion on this? I'll bet they would also be
> against it.
>
> What if someone uses the Fastcode library together with their own MM or if
> they override NewInstance in a class and don't dword align the end?

Don't misunderstand me. I too, am against this rule.

In my opinion, we should never read or write beyond the null terminator
byte. I know Borland themselves do read beyond the null terminator (in
_LStrCmp), but I believe even that was an oversight. Unfortunately that
oversight means that AnsiStrings's must also be padded to a DWORD boundary
in any replacement Memory Manager.

regards,
John


.

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