here's a malloc optimization (from Ralf Jung) that isn't as cute as the one from yesterdaypic.twitter.com/tXtvTrtva7
Yeah, I do @musllibc, FOSS & infosec stuff. But now is not the time for a mostly-/only-tech Twitter feed.
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here's a malloc optimization (from Ralf Jung) that isn't as cute as the one from yesterdaypic.twitter.com/tXtvTrtva7
I can’t find anything in C11 that forbids the max value of size_t being a lot smaller than my address space? If so, than we could build a system on which malloc(-1) can succeed?
The question isn't whether you can build a machine where it can succeed (easy, just define size_t too small), but if it can happen on the target one.
As-if rule does not allow you to make transformations based on some other theoretical target, only ones indistinguishable on the actual one.
You’re right. My response was more targeted towards the comment in the code, which assumes that malloc(-1) always fails.
On any system where arbitrary pointers can be preserved round-trip thru (size_t) cast, malloc(-1) necessarily fails.
This is observable at preprocessor level by defined(UINTPTR_MAX) && UINTPTR_MAX<=SIZE_MAX.
Proof is an immediate consequence of each array element having an address and pigeonhole principle.
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