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I think VLAs were a very good idea and they were not made optional because somebody thought they were a bad idea, but simply to make C11 easier to implement. V
by uecker 4y ago
I think VLAs were a very good idea and they were not made optional because somebody thought they were a bad idea, but simply to make C11 easier to implement. VLA can be dangerous when the size depends on external input an when implemented without stack probing.
- pjmlp 4y agoNo they are not. Google has paid the development effort for the Linux kernel to get rid of all VLA occurrences.
- cesarb 4y agoThe Linux kernel is a very different environment than user space; it has a very limited stack space (16 KiB IIRC), and the consequences of exceeding that are worse than in user space. > Google has paid the development effort for the Linux kernel to get rid of all VLA occurrences. IIRC, what they were really interested in getting rid of was not the normal VLA we're talking about, but something even more esoteric called VLAIS (variable length arrays in structures), which clang didn't support. See https://lwn.net/Articles/441018/ https://lwn.net/Articles/441018/ for a discussion about that.
- pjmlp 4y agoI have seen all Linux Plumber talks on the subject.
- uecker 4y agoI was tangentially involved in this and I think this was misguided.
- lelanthran 4y ago> when implemented without stack probing. I dunno how to probe the stack in standard C, and so I never used VLAs, nor allowed them because (I thought that) there was no way to determine if a VLA declaration would cause a stack overflow.