Allow atomic operations up to 32 bits

The ARMv5te platform does not have instruction-level support for atomics, however the kernel provides [user space helpers](https://www.kernel.org/doc/Documentation/arm/kernel_user_helpers.txt) which can be used to perform atomic operations. When linked with `libc`, the atomic symbols needed by Rust will be provided, rather than CPU level intrinsics.

As this target is specifically `linux` and `gnueabi`, it is reasonable to assume the Linux Kernel and libc will be available for the target. There is a large performance penalty, as we are not using CPU level intrinsics, however this penalty is likely preferable to not having the target at all.

I have used this change in a custom target (along with `xargo`) to build `std`, as well as a number of higher level crates.
This commit is contained in:
James Munns 2017-10-02 15:42:08 +02:00
parent 9ae6ed78ac
commit 1e26094bdd

View File

@ -27,8 +27,12 @@ pub fn target() -> TargetResult {
options: TargetOptions { options: TargetOptions {
features: "+soft-float,+strict-align".to_string(), features: "+soft-float,+strict-align".to_string(),
// No atomic instructions on ARMv5
max_atomic_width: Some(0), // Atomic operations provided when linked with libgcc.
// FIXME: If the following PR is merged, the atomic operations would be
// provided by compiler-builtins instead with no change of behavior:
// https://github.com/rust-lang-nursery/compiler-builtins/pull/115/files
max_atomic_width: Some(32),
abi_blacklist: super::arm_base::abi_blacklist(), abi_blacklist: super::arm_base::abi_blacklist(),
.. base .. base
} }