x86_64 MSVC coretest::ptr::test_variadic_fnptr: "error LNK2019: unresolved external symbol"

[hanna-kruppe]

I get a linker error when building coretest as part of the check step, or more specifically check-crate-std. The source of the problem is the test test_variadic_fnptr in src/coretest/ptr.rs, and the same error can be provoked by this self-contained program:

fn main() {
    extern "C" {
        fn printf(_: *const u8, ...);
    }
    let p: unsafe extern "C" fn(*const u8, ...) = printf;
    let _q = p.clone();
}

Some notes:

• compiling with optimizations will inline the clone and subsequently eliminate all the code including the part taking the address of printf, and then it compiles just fine.
• It appears related to being variadic, since fabs in place of printf worked just fine.
• It doesn't matter whether I take the address of the function or call it.

Meta

Reproduced with a rustup-provided nightly from August 21 and with the current bootstrap compiler (beta-2016-08-17).

[nagisa]

printf function is not a thing in MSVC. That test ought to be removed, because we test variadic functions in this test, including the function pointer.

[hanna-kruppe]

Why aren't the MSVC bots seeing the same error, then?

[nagisa]

Well existence of an actual function might depend on MSVC version, I guess. (e.g. the ulibc and the old libc implementation) Perhaps that’s the reason buildbots haven’t been failing?

printf function is not a thing in MSVC

I really meant to say that it is not guaranteed to be a function and may be a macro too (i.e. does not export a symbol to link to)

[retep998]

@nagisa If we can detect whether we're using a new enough MSVC version, we can tell the Rust to tell the linker to link legacy_stdio_definitions.lib which provides printf.

[nagisa]

Why? Just use the test helper we have exactly for this issue.

On Aug 29, 2016 7:06 AM, "Peter Atashian" notifications@github.com wrote:

@nagisa https://github.com/nagisa If we can detect whether we're using
a new enough MSVC version, we can tell the Rust to tell the linker to link
legacy_stdio_definitions.lib which provides printf.

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[retep998]

@nagisa Well sure, that's probably easier and more reliable.

[hanna-kruppe]

Are the test helpers available to coretest? Because test_variadic_fnptr tests some library features (hashing, clone, equality) that should, ideally, be tested there and not in a run-pass test.

Edit: They are not.