Make sure `kern_entry` at the beginning.

src/arch/riscv32/boot/entry.asm

@@ -1,4 +1,4 @@
-    .section .text,"ax",%progbits
+    .section .entry
     .globl kern_entry
 kern_entry:
     la sp, bootstacktop

src/arch/riscv32/boot/linker.ld

@@ -14,7 +14,8 @@ SECTIONS
     . = BASE_ADDRESS;
 
     .text : {
-        *(.text.kern_entry .text .stub .text.* .gnu.linkonce.t.*)
+        *(.entry)
+        *(.text .stub .text.* .gnu.linkonce.t.*)
     }
 
     PROVIDE(etext = .); /* Define the 'etext' symbol to this value */