link_section attribute misleadingly allowed on modules and impls

[Earlz]

The #[link_section] attribute seems to be allowed on modules and impl blocks, but it will not do anything. I would expect either all functions/statics within the module/impl to be placed into the specified link_section, but this does not happen.

Code used:

#[link_section = ".textaux1"]
mod foo{
    //#[link_section = ".textaux1"]
    pub fn testing() -> u32{
        20
    }
}
mod foo2{
    pub struct Whatever{}
    #[link_section = ".textaux1"]
    impl Whatever{
        //#[link_section = ".textaux1"]
        pub fn watt(&self) -> u32{
            50
        }
    }
}

I've verified the functions are linked in and not just optimized out etc. As-is the functions will be placed into the default .text section, but if I uncomment the link_section attributes then they are properly placed in the .textaux1 section. No compiler errors or warnings are generated

rustc version:
rustc 1.40.0-nightly (2daa404 2019-10-02)
binary: rustc
commit-hash: 2daa404
commit-date: 2019-10-02
host: x86_64-apple-darwin
release: 1.40.0-nightly
LLVM version: 9.0

[hannobraun]

The same seems to be true for extern functions. I would have expected the following code to link the extern function into .data, but it was linked into .text:

extern {
    #[link_section=".data"]
    #[inline(never)]
    fn write_half_page(address: *mut u32, words: *const u32);
}

No warning or error was emitted. The link_section attribute was just ignored, it seems.

[ehuss]

A warning for this has been added in #73461.

[bjorn3]

There is a future compat lint for this. Should this be closed?