rust/tests/run-make/std-core-cycle/foo.rs

#![crate_type = "cdylib"]

extern crate bar;

#[global_allocator]
static A: bar::A = bar::A;

#[no_mangle]
pub extern "C" fn a(a: u32, b: u32) -> u32 {
    a / b
}
rustc: Group linked libraries where needed This commit fixes a longstanding issue with the compiler with circular dependencies between libcore and libstd. The `core` crate requires at least one symbol, the ability to unwind. The `std` crate is the crate which actually defines this symbol, but the `std` crate also depends on the `core` crate. This circular dependency is in general disallowed in Rust as crates cannot have cycles amongst them. A special exception is made just for core/std, but this is also unfortunately incompatible with how GNU linkers work. GNU linkers will process undefined symbols in a left-to-right fashion, only actually linking an rlib like libstd if there are any symbols used from it. This strategy is incompatible with circular dependencies because if we otherwise don't use symbols from libstd we don't discover that we needed it until we're later processing libcore's symbols! To fix this GNU linkers support the `--start-group` and `--end-group` options which indicate "libraries between these markers may have circular dependencies amongst them. The linker invocation has been updated to automatically pass these arguments when we're invoking a GNU linker and automatically calculate where the arguments need to go (around libstd and libcore) Closes #18807 Closes #47074 2018-03-23 16:33:22 -05:00			`#![crate_type = "cdylib"]`

			`extern crate bar;`

			`#[global_allocator]`
			`static A: bar::A = bar::A;`

			`#[no_mangle]`
Update code to account for extern ABI requirement 2020-09-01 16:28:11 -05:00			`pub extern "C" fn a(a: u32, b: u32) -> u32 {`
rustc: Group linked libraries where needed This commit fixes a longstanding issue with the compiler with circular dependencies between libcore and libstd. The `core` crate requires at least one symbol, the ability to unwind. The `std` crate is the crate which actually defines this symbol, but the `std` crate also depends on the `core` crate. This circular dependency is in general disallowed in Rust as crates cannot have cycles amongst them. A special exception is made just for core/std, but this is also unfortunately incompatible with how GNU linkers work. GNU linkers will process undefined symbols in a left-to-right fashion, only actually linking an rlib like libstd if there are any symbols used from it. This strategy is incompatible with circular dependencies because if we otherwise don't use symbols from libstd we don't discover that we needed it until we're later processing libcore's symbols! To fix this GNU linkers support the `--start-group` and `--end-group` options which indicate "libraries between these markers may have circular dependencies amongst them. The linker invocation has been updated to automatically pass these arguments when we're invoking a GNU linker and automatically calculate where the arguments need to go (around libstd and libcore) Closes #18807 Closes #47074 2018-03-23 16:33:22 -05:00			`a / b`
			`}`