It very much is something that exists in hardware. One of the major reasons why people finally discovered the provenance UB lurking in the standard is because of the CHERI architecture.
So it's something that exists in some hardware. Are you claiming that it exists in all hardware, and we only realized that because of CHERI? Or are you claiming that it exists in CHERI hardware, but not in others.
If it only exists in some hardware, how should the standard deal with that?
> If it only exists in some hardware, how should the standard deal with that?
Generally seems to me the C standard makes things like that UB. Signed integer overflow, for example. Implemented as wrapping two's-complement on modern architectures, defined as such in many modern languages, but UB in C due to ongoing support for niche architectures.
The issues around pointer provenance are inherent to the C abstract machine. It's a much more immediate show-stopper on architectures that don't have a flat address space, and the C abstract machine doesn't assume a flat address space because it supports architecture where that's not true. My understanding is that reflects some oddball historical architectures that aren't relevant anymore, nowadays that includes CHERI.
AnimalMuppet|6 months ago
If it only exists in some hardware, how should the standard deal with that?
lmkg|6 months ago
Generally seems to me the C standard makes things like that UB. Signed integer overflow, for example. Implemented as wrapping two's-complement on modern architectures, defined as such in many modern languages, but UB in C due to ongoing support for niche architectures.
The issues around pointer provenance are inherent to the C abstract machine. It's a much more immediate show-stopper on architectures that don't have a flat address space, and the C abstract machine doesn't assume a flat address space because it supports architecture where that's not true. My understanding is that reflects some oddball historical architectures that aren't relevant anymore, nowadays that includes CHERI.
pjmlp|6 months ago