start initial irq handling

+ Still lots todo, and I'm not entirely sure how I should handle program
  space switches (mainly since the kernel uses the process' stack, maybe
		  it shouldn't?)

1 files changed, 64 insertions, 0 deletions

diff --git a/arch/riscv64/kernel/head.S b/arch/riscv64/kernel/head.S
new file mode 100644
index 0000000..b8ad295
--- /dev/null
+++ b/arch/riscv64/kernel/head.S
@@ -0,0 +1,64 @@
+#include <csr.h>
+
+.section .text
+.global handle_irq
+handle_irq:
+	addi    sp,sp,-144
+	sd      ra,136(sp)
+	sd      t0,128(sp)
+	sd      t1,120(sp)
+	sd      t2,112(sp)
+	sd      s0,104(sp)
+	sd      a0,96(sp)
+	sd      a1,88(sp)
+	sd      a2,80(sp)
+	sd      a3,72(sp)
+	sd      a4,64(sp)
+	sd      a5,56(sp)
+	sd      a6,48(sp)
+	sd      a7,40(sp)
+	sd      t3,32(sp)
+	sd      t4,24(sp)
+	sd      t5,16(sp)
+	sd      t6,8(sp)
+	addi    s0,sp,144
+	/* load supervisor cause */
+	csrr s4, CSR_SCAUSE
+	/* interrupts fall through, exceptions jump */
+	bge s4, zero, handle_exception
+	/* TODO: handle interrupts */
+	j restore_all
+
+handle_exception:
+	li t0, EXC_SYSCALL
+	/* system exceptions fall through, syscalls jump */
+	beq s4, t0, handle_syscall
+	j	restore_all
+
+handle_syscall:
+	jal	syscall_dispatch
+	j	restore_noreturn
+
+restore_all:
+	ld      a0,96(sp)
+
+restore_noreturn:
+	ld      ra,136(sp)
+	ld      t0,128(sp)
+	ld      t1,120(sp)
+	ld      t2,112(sp)
+	ld      s0,104(sp)
+	ld      a1,88(sp)
+	ld      a2,80(sp)
+	ld      a3,72(sp)
+	ld      a4,64(sp)
+	ld      a5,56(sp)
+	ld      a6,48(sp)
+	ld      a7,40(sp)
+	ld      t3,32(sp)
+	ld      t4,24(sp)
+	ld      t5,16(sp)
+	ld      t6,8(sp)
+	addi    sp,sp,144
+	/* assume supervisor for now */
+	sret