[PATCH v6 4/6] xen/riscv: introduce trap_init()

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
Reviewed-by: Alistair Francis <alistair.francis@xxxxxxx>
---
Changes in V6:
 - trap_init() is now called after enabling the MMU.
 - Add additional explanatory comments.
---
Changes in V5:
  - Nothing changed
---
Changes in V4:
  - Nothing changed
---
Changes in V3:
  - Nothing changed
---
Changes in V2:
  - Rename setup_trap_handler() to trap_init().
  - Add Reviewed-by to the commit message.
---
 xen/arch/riscv/include/asm/traps.h |  1 +
 xen/arch/riscv/setup.c             |  3 +++
 xen/arch/riscv/traps.c             | 25 +++++++++++++++++++++++++
 3 files changed, 29 insertions(+)

diff --git a/xen/arch/riscv/include/asm/traps.h 
b/xen/arch/riscv/include/asm/traps.h
index f3fb6b25d1..f1879294ef 100644
--- a/xen/arch/riscv/include/asm/traps.h
+++ b/xen/arch/riscv/include/asm/traps.h
@@ -7,6 +7,7 @@
 
 void do_trap(struct cpu_user_regs *cpu_regs);
 void handle_trap(void);
+void trap_init(void);
 
 #endif /* __ASSEMBLY__ */
 
diff --git a/xen/arch/riscv/setup.c b/xen/arch/riscv/setup.c
index 845d18d86f..1cae0e5ccc 100644
--- a/xen/arch/riscv/setup.c
+++ b/xen/arch/riscv/setup.c
@@ -3,6 +3,7 @@
 
 #include <asm/early_printk.h>
 #include <asm/mm.h>
+#include <asm/traps.h>
 
 /* Xen stack for bringing up the first CPU. */
 unsigned char __initdata cpu0_boot_stack[STACK_SIZE]
@@ -25,6 +26,8 @@ void __init noreturn start_xen(unsigned long bootcpu_id,
 
 void __init noreturn cont_after_mmu_is_enabled(void)
 {
+    trap_init();
+
     early_printk("All set up\n");
 
     for ( ;; )
diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c
index ea1012e83e..48c1059954 100644
--- a/xen/arch/riscv/traps.c
+++ b/xen/arch/riscv/traps.c
@@ -12,6 +12,31 @@
 #include <asm/processor.h>
 #include <asm/traps.h>
 
+#define cast_to_bug_frame(addr) \
+    (const struct bug_frame *)(addr)
+
+/*
+ * Initialize the trap handling.
+ *
+ * The function is called after MMU is enabled.
+ */
+void trap_init(void)
+{
+    /*
+     * When the MMU is off, addr varialbe will be a physical address otherwise
+     * it would be a virtual address.
+     *
+     * It will work fine as:
+     *  - access to addr is PC-relative.
+     *  - -nopie is used. -nopie really suppresses the compiler emitting
+     *    code going through .got (which then indeed would mean using absolute
+     *    addresses).
+     */
+    unsigned long addr = (unsigned long)&handle_trap;
+
+    csr_write(CSR_STVEC, addr);
+}
+
 static const char *decode_trap_cause(unsigned long cause)
 {
     static const char *const trap_causes[] = {
-- 
2.40.1