fix(rt): avoid compilation of multiple architecture support functions in the same chip SoC feature

On Rust documents both the functions are kept, however.

Signed-off-by: Zhouqi Jiang <[email protected]>

Author: luojia65

allwinner-rt/src/arch/andes_a27l2.rs

@@ -1,9 +1,11 @@
 /// Jump over head data to executable code.
 ///
 /// TODO Andes start code.
-#[cfg(feature = "v821")]
+#[cfg_attr(
+    any(all(feature = "v821", target_arch = "riscv64"), doc),
+    unsafe(link_section = ".text.entry")
+)]
 #[unsafe(naked)]
-#[unsafe(link_section = ".text.entry")]
 pub unsafe extern "C" fn start() -> ! {
     const STACK_SIZE: usize = 8 * 1024;
     #[unsafe(link_section = ".bss.uninit")]

allwinner-rt/src/arch/thead_c906.rs

@@ -6,9 +6,11 @@
 ///
 /// NOTE: `mxstatus` is a custom T-Head register. Do not confuse with `mstatus`.
 /// It allows for configuring special eXtensions. See further below for details.
-#[cfg(any(all(feature = "d1", target_arch = "riscv64"), doc))]
+#[cfg_attr(
+    any(all(feature = "d1", target_arch = "riscv64"), doc),
+    unsafe(link_section = ".text.entry")
+)]
 #[unsafe(naked)]
-#[unsafe(link_section = ".text.entry")]
 pub unsafe extern "C" fn thead_c906_start() -> ! {
     use super::riscv_fpu::init_floating_point;
     use crate::main;
@@ -60,11 +62,6 @@ pub unsafe extern "C" fn thead_c906_start() -> ! {
     )
 }
 
-#[cfg(not(any(all(feature = "d1", target_arch = "riscv64"), doc)))]
-pub unsafe extern "C" fn thead_c906_start() -> ! {
-    unimplemented!()
-}
-
 /// Stop a T-Head C906 core.
 #[unsafe(naked)]
 pub unsafe extern "C" fn thead_c906_halt() -> ! {