[PATCH v10 2/5] xen/riscv: introduce decode_cause() stuff

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

The patch introduces stuff needed to decode a reason of an
exception.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
Acked-by: Alistair Francis <alistair.francis@xxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Changes in V10:
 - add Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Changes in V9:
 - This patch was reverted as breaks both release and randconfig builds.
   I don't see the failures now. ( probably it was because of printk usage
   which was not ready at that moment ).
 - drop inclusion of <asm/csr.h> and <asm/early_printk.h>
 - add <asm/riscv_encoding.h> for CAUSE_* in decode_trap_cause().
---
Changes in V8:
  - fix typo in return string from decode_reserved_interrupt_cause
  - add Acked-by: Alistair Francis <alistair.francis@xxxxxxx>
---
Changes in V7:
 - Nothing changed. Only rebase.
---
Changes in V6:
 - Remove usage of LINK_TO_LOAD() due to the MMU being enabled first.
 - Change early_printk() to printk()
---
Changes in V5:
  - Remove <xen/error.h> from riscv/traps/c as nothing would require
    inclusion.
  - decode_reserved_interrupt_cause(), decode_interrupt_cause(), decode_cause, 
do_unexpected_trap()
    were made as static they are expected to be used only in traps.c
  - use LINK_TO_LOAD() for addresses which can be linker time relative.
---
Changes in V4:
  - fix string in decode_reserved_interrupt_cause()
---
Changes in V3:
  - Nothing changed
---
Changes in V2:
  - Make decode_trap_cause() more optimization friendly.
  - Merge the pathc which introduces do_unexpected_trap() to the current one.
---
 xen/arch/riscv/traps.c | 80 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 79 insertions(+), 1 deletion(-)

diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c
index 5415cf8d90..37cec40dfa 100644
--- a/xen/arch/riscv/traps.c
+++ b/xen/arch/riscv/traps.c
@@ -9,13 +9,91 @@
 #include <xen/sched.h>
 
 #include <asm/processor.h>
+#include <asm/riscv_encoding.h>
 #include <asm/traps.h>
 
-void do_trap(struct cpu_user_regs *cpu_regs)
+static const char *decode_trap_cause(unsigned long cause)
+{
+    static const char *const trap_causes[] = {
+        [CAUSE_MISALIGNED_FETCH] = "Instruction Address Misaligned",
+        [CAUSE_FETCH_ACCESS] = "Instruction Access Fault",
+        [CAUSE_ILLEGAL_INSTRUCTION] = "Illegal Instruction",
+        [CAUSE_BREAKPOINT] = "Breakpoint",
+        [CAUSE_MISALIGNED_LOAD] = "Load Address Misaligned",
+        [CAUSE_LOAD_ACCESS] = "Load Access Fault",
+        [CAUSE_MISALIGNED_STORE] = "Store/AMO Address Misaligned",
+        [CAUSE_STORE_ACCESS] = "Store/AMO Access Fault",
+        [CAUSE_USER_ECALL] = "Environment Call from U-Mode",
+        [CAUSE_SUPERVISOR_ECALL] = "Environment Call from S-Mode",
+        [CAUSE_MACHINE_ECALL] = "Environment Call from M-Mode",
+        [CAUSE_FETCH_PAGE_FAULT] = "Instruction Page Fault",
+        [CAUSE_LOAD_PAGE_FAULT] = "Load Page Fault",
+        [CAUSE_STORE_PAGE_FAULT] = "Store/AMO Page Fault",
+        [CAUSE_FETCH_GUEST_PAGE_FAULT] = "Instruction Guest Page Fault",
+        [CAUSE_LOAD_GUEST_PAGE_FAULT] = "Load Guest Page Fault",
+        [CAUSE_VIRTUAL_INST_FAULT] = "Virtualized Instruction Fault",
+        [CAUSE_STORE_GUEST_PAGE_FAULT] = "Guest Store/AMO Page Fault",
+    };
+
+    if ( cause < ARRAY_SIZE(trap_causes) && trap_causes[cause] )
+        return trap_causes[cause];
+    return "UNKNOWN";
+}
+
+static const char *decode_reserved_interrupt_cause(unsigned long irq_cause)
+{
+    switch ( irq_cause )
+    {
+    case IRQ_M_SOFT:
+        return "M-mode Software Interrupt";
+    case IRQ_M_TIMER:
+        return "M-mode Timer Interrupt";
+    case IRQ_M_EXT:
+        return "M-mode External Interrupt";
+    default:
+        return "UNKNOWN IRQ type";
+    }
+}
+
+static const char *decode_interrupt_cause(unsigned long cause)
+{
+    unsigned long irq_cause = cause & ~CAUSE_IRQ_FLAG;
+
+    switch ( irq_cause )
+    {
+    case IRQ_S_SOFT:
+        return "Supervisor Software Interrupt";
+    case IRQ_S_TIMER:
+        return "Supervisor Timer Interrupt";
+    case IRQ_S_EXT:
+        return "Supervisor External Interrupt";
+    default:
+        return decode_reserved_interrupt_cause(irq_cause);
+    }
+}
+
+static const char *decode_cause(unsigned long cause)
+{
+    if ( cause & CAUSE_IRQ_FLAG )
+        return decode_interrupt_cause(cause);
+
+    return decode_trap_cause(cause);
+}
+
+static void do_unexpected_trap(const struct cpu_user_regs *regs)
 {
+    unsigned long cause = csr_read(CSR_SCAUSE);
+
+    printk("Unhandled exception: %s\n", decode_cause(cause));
+
     die();
 }
 
+void do_trap(struct cpu_user_regs *cpu_regs)
+{
+    do_unexpected_trap(cpu_regs);
+}
+
 void vcpu_show_execution_state(struct vcpu *v)
 {
     BUG_ON("unimplemented");
-- 
2.45.2