xen/riscv: initialize .bss section

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Bobby Eshleman <bobbyeshleman@gmail.com>

xen/arch/riscv/riscv64/head.S

@@ -1,3 +1,4 @@
+#include <asm/asm.h>
 #include <asm/riscv_encoding.h>
 
         .section .text.header, "ax", %progbits
@@ -18,6 +19,14 @@ ENTRY(start)
         li      t0, SSTATUS_FS
         csrc    CSR_SSTATUS, t0
 
+        /* Clear the BSS */
+        la      t3, __bss_start
+        la      t4, __bss_end
+.L_clear_bss:
+        REG_S   zero, (t3)
+        add     t3, t3, __SIZEOF_POINTER__
+        bltu    t3, t4, .L_clear_bss
+
         la      sp, cpu0_boot_stack
         li      t0, STACK_SIZE
         add     sp, sp, t0

xen/arch/riscv/setup.c

@@ -7,6 +7,14 @@
 unsigned char __initdata cpu0_boot_stack[STACK_SIZE]
     __aligned(STACK_SIZE);
 
+/*  
+ * To be sure that .bss isn't zero. It will simplify code of
+ * .bss initialization.
+ * TODO:
+ *   To be deleted when the first real .bss user appears
+ */
+int dummy_bss __attribute__((unused));
+
 void __init noreturn start_xen(unsigned long bootcpu_id,
                                paddr_t dtb_addr)
 {