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Comment by adamwk | Hacker News Reader

Crashing on shared access is the safe thing to do

An intentional exit by a runtime is a safe crash. A segfault is not, and is here a clear sign that memory safety has been violated.

I guess I was thinking specifically of the swift case where values have exclusive access enforcement. Normally caught by a compiler, they will safely crash if the compiler didn’t catch it. I think the only way to segfault would be by using Unsafe*Pointer types, which are explicitly marked unsafe

Yeah it's not the segfault that's bad, it's when it's when the write to address 0x20001854 succeeds and now some hapless postal clerk is going to jail.

"Crashing" is a very positive spin. "The heap getting the corrupted until it was killed by the operating system" is another interpretation.

a segfault is completely unintentional. Had the kernel been older it could be used to execute code.

> a segfault is completely unintentional

Usually, but not always! https://jcdav.is/2015/10/06/SIGSEGV-as-control-flow/

> Faulted trying to access 0x10 - the offset in the string we were trying to read from :)

Is guaranteed that every offset you can try to read is guaranteed to create a segfault?

> Is guaranteed that every offset you can try to read is guaranteed to create a segfault?

The offset is fixed as part of the compiled code; the JVM can enforce that it's less than 4k (otherwise it can use an explicit NULL check), and that the first 4k page is always unmapped.

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