raw pointer produced illegal instruction on X86 and X86-64 but not ARM

[mark3982]

rustc 0.13.0-dev (dbc379a66 2014-12-03 18:52:48 +0000)
binary: rustc
commit-hash: dbc379a66eae8504b663b0032da518595335d872
commit-date: 2014-12-03 18:52:48 +0000
host: x86_64-unknown-linux-gnu
release: 0.13.0-dev

fn main() {
    unsafe {
        let mem: *mut u8 = 1234 as *mut u8;
        *mem = 6u as u8;
    }
}

The following code will produce correct machine instructions for arm-unknown-linux-gnueabi but produces an illegal instruction on X86 (i686-unknown-linux-gnu) and X86-64.

I can try testing on the very latest development version tomorrow, but I imagine someone will beat me to it as it takes me a long time to build.

[huonw]

The asm rust/llvm produces (rustc -O --emit=asm) is:

_ZN4main20h7890cd32b0d93ad4eaaE:
    .cfi_startproc
    movb    $6, 1234
    retq

as expected (this is essentially identical to what GCC and Clang produce for the equivalent C program).

The illegal instruction error seems to be related to our current runtime catching/handling the segfault signal, e.g. changing the code to

#[start]
fn main(_: int, _: *const *const u8) -> int {
    unsafe {
        *(1234 as *mut u8) = 6;
    }
    0
}

gives a segfault which is the expected output: writing to some "random" piece of memory is unlikely to work well.

Closing as not-a-bug, feel free to reopen if I've misinterpreted you.