I read this, and thought it was kind of all over the place. Even the first “falsehood” about always immediately crashing is answered as “true for some languages but not some others”. Even the motion of superlatives in CS like “always” and “never” rarely hold, including this very sentence and almost certainly when talking about multiple programming languages.

And on that point, it’s a minor quibble, but while Go’s nil pointers are similar to C null pointers and Rust’s null raw pointers, it’s a strange thing to have the title be about falsehoods about null pointers.

But then much of the other supposed falsehoods are addressed only for the C language, such as null deference being UB or not.

1. On platforms where the null pointer has address 0, C objects may not be placed at address 0.

I would like to see a ©itation [pun intended] for this being a supposed falsehood, since my understanding is that if an implementation uses 0x0 as the null pointer, then the check for a null pointer is to check if it’s equal to 0x0, which would require that no “thing” in C use that address.

Macromedia Flash Action Script was the first language I saw that could have a RCE vulnerability caused by null pointer dereference.

Thank god HTML5 media killed Flash.

Before virtual memory was a thing, almost all memory was accessible.

Virtual memory has nothing to do with whether 0 is a valid address. You can have a CPU where it is valid, or one where it isn’t and you’ll get an access fault if you try to access it. You can also have virtual memory where page 0 is mappable, or not.

I think the author knew that, based on the later points so it’s probably just bad wording. Interesting point about wasm too!

Small nit:

CHERI is even weirder. CHERI pointers store 128-bit capabilities in addition to the 64-bit address we’re used to

The 128-bit capability (actually 129 since there’s a tag bit) includes the address. It’s 64-bit address + 64-bit metadata + 1-bit tag = 129-bit capability.

Very misleading writing style IMO. I would say most of their bullet points ARE actually true in most cases… they just keep bringing up somewhat rare/exotic exceptions as a way to call it a “falsehood”.