SIGILL Illegal instrucion on Vec::reserve(2^32+1)

[payload]

on 64bit machine, compiled for 64bit. test case:

fn main() {
    let big: uint = 1024*1024*1024*4 + 1; // 2^32+1
    let mut vec: Vec<u8> = Vec::new();
    vec.reserve(big);
}

likely related: #18726

[Gankra]

CC me

[thestinger]

Rust handles out-of-memory by aborting like this.

[Gankra]

Oh yeah, I guess you would need like 16-32 gigs of ram in a 64-bit machine on most OSes to successfully complete that reserve (which asks for an 8GB array)?

[thestinger]

It will work if you enable full overcommit, but not by default on Linux.

[payload]

It asks for 4GB+1B. A malloc in C of 4GB+1B works perfectly fine, cause it is just a request for memory to the kernel and not an actual usage of this memory. to the best of my knowledge in C on Linux one would have to write at each allocated page to actual consume those 4GB+1B.

[Gankra]

@payload If you want 4GB + 1B use reserve_exact. reserve rounds allocations for amortization.

[Gankra]

Admittedly, we could maybe make reserve check if the given number is at least the size of the current allocation, and call reserve_exact if it is.

Also note that Rust uses its own instance of jemalloc, and not the system allocator.

[thestinger]

to the best of my knowledge in C on Linux one would have to write at each allocated page to actual consume

Linux supports full overcommit and virtual memory accounting but doesn't use either by default. It defaults to overcommit with heuristics returning allocation errors in some cases.