Re: Signed int overflow behavior in the security context

[prj at po dot cwru dot edu (Paul Jarc)]

Paul Schlie <schlie@comcast.net> wrote:
> Paul Jarc wrote:
>> As noted in the defect report, a trap representation can have the
>> same bit pattern as a valid value.  Trapness depends not just on
>> the bit pattern, but also how the bit pattern was produced.
>
> - that's not what is says

Did you read it?

# Implementations are permitted to track the origins of a bit-pattern
# and treat those representing an indeterminate value as distinct from
# those representing a determined value.

> a pointer value may be/become a trap representation [...]

That is also true, but there is more than that.

> is required to be well specified [...] as otherwise the language
> couldn't be utilized to write even the most hardware drivers
> required of all computer systems.

In a sense, the language *can't* be used to write most hardware
drivers.  Drivers do invoke undefined behavior - that is, the standard
makes no guarantees about their behavior - but the particular platform
they are targeted for makes its own guarantees, so the code is still
useful, even though it is not strictly conforming C.


paul