libc projection

core/c/libc/errno.odin

@@ -0,0 +1,43 @@
+package libc
+
+// 7.5 Errors
+
+foreign import libc "system:c"
+
+// C11 standard only requires the definition of:
+//	EDOM,
+//	EILSEQ
+//	ERANGE
+when ODIN_OS == "linux" || ODIN_OS == "freebsd" {
+	@(private="file")
+	@(default_calling_convention="c")
+	foreign libc {
+		@(link_name="__libc_errno_location")
+		_get_errno :: proc() -> ^int ---;
+	}
+
+	EDOM   :: 33;
+	EILSEQ :: 84;
+	ERANGE :: 34;
+}
+
+when ODIN_OS == "windows" {
+	@(private="file")
+	@(default_calling_convention="c")
+	foreign libc {
+		@(link_name="_errno")
+		_get_errno :: proc() -> ^int ---;
+	}
+
+	EDOM   :: 33;
+	EILSEQ :: 42;
+	ERANGE :: 34;
+}
+
+// Odin has no way to make an identifier "errno" behave as a function call to
+// read the value, or to produce an lvalue such that you can assign a different
+// error value to errno. To work around this, just expose it as a function like
+// it actually is.
+errno :: #force_inline proc() -> ^int {
+	return _get_errno();
+}