pub static disappears if only used from asm

[kmcallister]

#[feature(asm)];

#[no_mangle]
pub static arr: [u8, ..16] = [0, ..16];

fn main() {
    unsafe {
        asm!("movups arr, %xmm0" ::: "xmm0");
    }
}

$ rustc -v
rustc 0.10-pre (68a4f7d 2014-02-24 12:42:02 -0800)
host: x86_64-unknown-linux-gnu

$ rustc -O foo.rs
error: linking with `cc` failed: exit code: 1
note: cc arguments: [...]
note: foo.o: In function `main::hcaa4d83fe49d03ddnaa::v0.0':
foo.rs:(.text+0x29): undefined reference to `arr'
collect2: error: ld returned 1 exit status

error: aborting due to previous error

Adding an unused constraint "r"(&arr) fixes it, as does passing &arr to test::black_box (which does basically that).

[steveklabnik]

Traige: still true

[Stebalien]

Still an issue. Updated example:

#![feature(asm)]

#[no_mangle]
pub static arr: [u8; 16] = [0; 16];

fn main() {
    unsafe {
        asm!("movups arr, %xmm0" ::: "xmm0");
    }
}

[brson]

Error is different now:

rustc 1.17.0-nightly (b1e31766d 2017-03-03)
warning: static variable `arr` should have an upper case name such as `ARR`
 --> <anon>:4:1
  |
4 | pub static arr: [u8; 16] = [0; 16];
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(non_upper_case_globals)] on by default

error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib" "./out.0.o" "-o" "./out" "-Wl,--gc-sections" "-pie" "-nodefaultlibs" "-L" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "-Wl,-Bdynamic" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-9a66b6a343d52844.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/librand-6bc49e032a89c77d.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcollections-a2a467c3ca3b6479.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_unicode-e54225ff8f33e08f.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-9d79f761aa668a33.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-2beb731af7a6faec.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-ce7b9706e1719f27.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc_jemalloc-4b74d6f2808677d3.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-95af4192ed69a1c8.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-cd0ca85e71f914ca.rlib" "/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-0bf24067248742a8.rlib" "-l" "dl" "-l" "rt" "-l" "pthread" "-l" "gcc_s" "-l" "pthread" "-l" "c" "-l" "m" "-l" "rt" "-l" "util"
  = note: /usr/bin/ld: ./out.0.o: relocation R_X86_64_32S against `arr' can not be used when making a shared object; recompile with -fPIC
          ./out.0.o: error adding symbols: Bad value
          collect2: error: ld returned 1 exit status
          

error: aborting due to previous error

[nikomatsakis]

The correct way to do this is to pass the array as a constrained variable (per @nagisa, who can provide more details) so that the compiler knows about the fact that arr is used (I imagine the fact that it is stripped is related to building a binary, not a library, as well). Closing.

[nagisa]

Namely the code should be looking something like this:

asm!("movups $0, %xmm0" : "something"(arr) :: "xmm0")

instead.