[PATCH v5 4/7] xen/riscv: introduce decode_cause() stuff

[Oleksii Kurochko <oleksii.kurochko@gmail.com>]

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

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
---
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 | 87 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 86 insertions(+), 1 deletion(-)

diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c
index ccd3593f5a..8a1529e0c5 100644
--- a/xen/arch/riscv/traps.c
+++ b/xen/arch/riscv/traps.c
@@ -4,10 +4,95 @@
  *
  * RISC-V Trap handlers
  */
+
+#include <xen/lib.h>
+
+#include <asm/boot-info.h>
+#include <asm/csr.h>
+#include <asm/early_printk.h>
 #include <asm/processor.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);
+
+    early_printk("Unhandled exception: ");
+    early_printk(LINK_TO_LOAD(decode_cause(cause)));
+    early_printk("\n");
+
     die();
 }
+
+void do_trap(struct cpu_user_regs *cpu_regs)
+{
+    do_unexpected_trap(cpu_regs);
+}
-- 
2.39.2