check current execution mode

1 files changed, 22 insertions, 0 deletions

diff --git a/kernel.c b/kernel.c
index 555aa47..b387a10 100644
--- a/kernel.c
+++ b/kernel.c
@@ -36,6 +36,28 @@ void kernel_main(uint32_t r0, uint32_t r1, uint32_t atags)
   }
 
   uart_puts(paging);
+
+  uint32_t CPSR;
+  // get content of current program status register to check the current
+  // processor mode
+  asm("mrs %0, cpsr" : "=r" (CPSR) :: "memory");
+
+  char *mode;
+  
+  switch(CPSR & 0x1f) /* lowest 5 bits indicate processor mode */ {
+  case 0x10 : mode = "User (PL0)"; break;
+  case 0x11 : mode = "FIQ (PL1)"; break;
+  case 0x12 : mode = "IRQ (PL1)"; break;
+  case 0x13 : mode = "Supervisor (PL1)"; break;
+  case 0x16 : mode = "Monitor (PL1)"; break;
+  case 0x17 : mode = "Abort (PL1)"; break;
+  case 0x1a : mode = "Hyp (PL2)"; break;
+  case 0x1b : mode = "Undefined (PL1)"; break;
+  case 0x1f : mode = "System (PL1)"; break;
+  default : mode = "Unknown mode"; break;
+  }
+
+  uart_puts(mode);
   
   while (1)
     uart_putc(uart_getc());