feat: weakly provide the sys_errno_location function for all errno …

…access

src/errno.rs

@@ -396,26 +396,39 @@ pub const ERFKILL: i32 = 132;
 /// Robust mutexes: Memory page has hardware error
 pub const EHWPOISON: i32 = 133;
 
+/// Returns the pointer to `errno`.
 #[cfg(not(any(feature = "common-os", feature = "nostd")))]
-#[thread_local]
-pub(crate) static ERRNO: core::cell::UnsafeCell<i32> = core::cell::UnsafeCell::new(0);
+#[unsafe(no_mangle)]
+#[linkage = "weak"]
+pub extern "C" fn sys_errno_location() -> *mut i32 {
+	use core::cell::UnsafeCell;
+
+	#[thread_local]
+	static ERRNO: UnsafeCell<i32> = UnsafeCell::new(0);
+
+	ERRNO.get()
+}
 
 /// Get the error number from the thread local storage
+///
+/// Soft-deprecated in favor of using [`sys_errno_location`].
 #[cfg(not(feature = "nostd"))]
 #[unsafe(no_mangle)]
 pub extern "C" fn sys_get_errno() -> i32 {
 	sys_errno()
 }
 
 /// Get the error number from the thread local storage
+///
+/// Soft-deprecated in favor of using [`sys_errno_location`].
 #[cfg(not(feature = "nostd"))]
 #[unsafe(no_mangle)]
 pub extern "C" fn sys_errno() -> i32 {
 	cfg_if::cfg_if! {
 		if #[cfg(feature = "common-os")] {
 			0
 		} else {
-			unsafe { ERRNO.get().read() }
+			unsafe { *sys_errno_location() }
 		}
 	}
 }
@@ -435,7 +448,7 @@ pub(crate) trait ToErrno {
 					let _ = errno;
 				} else {
 					unsafe {
-						ERRNO.get().write(errno);
+						*sys_errno_location() = errno;
 					}
 				}
 			}

src/lib.rs

@@ -9,6 +9,7 @@
 )]
 #![cfg_attr(target_arch = "x86_64", feature(abi_x86_interrupt))]
 #![feature(allocator_api)]
+#![feature(linkage)]
 #![feature(linked_list_cursors)]
 #![feature(map_try_insert)]
 #![feature(maybe_uninit_as_bytes)]