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by rapidlua 1347 days ago
This is unfortunately ABI-altering, therefore it won’t be possible to selectively enable for projects that want it. It’s a distribution that has either to bite the bullet and say “we are going to pessimize all C++ software”, or err on the safe side and leave it disabled.

The warning about pointer arithmetic is most likely suppressable per compilation unit (for things like tagged pointers).
2 comments
gpderetta 1347 days ago
It is mentioned that the fixit will create forwarding overloads (marked deprecated) automatically, so the old interface is preserved for API and ABI compatibility.
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olliej 1347 days ago
What is the ABI altering concern? Switching from pointer+length->span? Because yeah that is alas a source of suffering.

> “we are going to pessimize all C++ software”

Could you clarify?

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rapidlua 1347 days ago
As of today, vector’s iterator is just a pointer. You need more than just a pointer to detect out of bounds accesses. It makes old binaries incompatible with new binaries. It also means that you can’t mix and match, it must be either a or b.

Hence you can’t make the change incrementally, which is a big risk.

Concerning Linux distributions, I seriously doubt if they have resources to assess the performance impact across the wide range of software.

Concerning performance impact, we end up with more instructions and more memory accesses and increased register pressure. This has a chance to make things slower.

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pabs3 1347 days ago
Perhaps you could keep ABI compatible using with versioned symbols?
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gpderetta 1347 days ago
If the functions are separate overloads there is no need of versioning in the first place.

On the other hand if you change the layout of structures (like it would be the case for bound checked pointers), it is much much harder. GCC has ABI tags, but they only help a bit.

In any case nobody is going to bound check iterators by default, these already exists when using whatever debug standard library your compiler provides and they are orders of magnitude slower than unchecked iterators.

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chris_wot 1347 days ago
Can it not work on individual software programs though? And use a shim to access non-safe buffers?
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