[PATCH v3 3/6] xen/riscv: introduce stack stuff

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

The patch introduces and sets up a stack in order to go to C environment

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in V3:
    - reorder headers in alphabetical order
    - merge changes related to start_xen() function from "[PATCH v2 7/8]
      xen/riscv: print hello message from C env" to this patch
    - remove unneeded parentheses in definition of STACK_SIZE
---
Changes in V2:
    - introduce STACK_SIZE define.
    - use consistent padding between instruction mnemonic and operand(s)
---
 xen/arch/riscv/Makefile             |  1 +
 xen/arch/riscv/include/asm/config.h |  2 ++
 xen/arch/riscv/riscv64/head.S       |  6 +++++-
 xen/arch/riscv/setup.c              | 14 ++++++++++++++
 4 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 xen/arch/riscv/setup.c

diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
index 248f2cbb3e..5a67a3f493 100644
--- a/xen/arch/riscv/Makefile
+++ b/xen/arch/riscv/Makefile
@@ -1,4 +1,5 @@
 obj-$(CONFIG_RISCV_64) += riscv64/
+obj-y += setup.o
 
 $(TARGET): $(TARGET)-syms
        $(OBJCOPY) -O binary -S $< $@
diff --git a/xen/arch/riscv/include/asm/config.h 
b/xen/arch/riscv/include/asm/config.h
index 0370f865f3..763a922a04 100644
--- a/xen/arch/riscv/include/asm/config.h
+++ b/xen/arch/riscv/include/asm/config.h
@@ -43,6 +43,8 @@
 
 #define SMP_CACHE_BYTES (1 << 6)
 
+#define STACK_SIZE PAGE_SIZE
+
 #endif /* __RISCV_CONFIG_H__ */
 /*
  * Local variables:
diff --git a/xen/arch/riscv/riscv64/head.S b/xen/arch/riscv/riscv64/head.S
index 990edb70a0..d444dd8aad 100644
--- a/xen/arch/riscv/riscv64/head.S
+++ b/xen/arch/riscv/riscv64/head.S
@@ -1,4 +1,8 @@
         .section .text.header, "ax", %progbits
 
 ENTRY(start)
-        j  start
+        la      sp, cpu0_boot_stack
+        li      t0, STACK_SIZE
+        add     sp, sp, t0
+
+        tail    start_xen
diff --git a/xen/arch/riscv/setup.c b/xen/arch/riscv/setup.c
new file mode 100644
index 0000000000..13e24e2fe1
--- /dev/null
+++ b/xen/arch/riscv/setup.c
@@ -0,0 +1,14 @@
+#include <xen/compile.h>
+#include <xen/init.h>
+
+/* Xen stack for bringing up the first CPU. */
+unsigned char __initdata cpu0_boot_stack[STACK_SIZE]
+    __aligned(STACK_SIZE);
+
+void __init noreturn start_xen(void)
+{
+    for ( ;; )
+        asm volatile ("wfi");
+
+    unreachable();
+}
-- 
2.38.1