static inline int32_t
syscall(int num, int check, uint32_t a1, uint32_t a2, uint32_t a3, uint32_t a4, uint32_t a5)
{
	int32_t ret;

	// Generic system call: pass system call number in AX,
	// up to five parameters in DX, CX, BX, DI, SI.
	// Interrupt kernel with T_SYSCALL.
	//
	// The "volatile" tells the assembler not to optimize
	// this instruction away just because we don't use the
	// return value.
	// 
	// The last clause tells the assembler that this can
	// potentially change the condition codes and arbitrary
	// memory locations.

	asm volatile("syscall\n"
		: "=a" (ret)
		: "a" (num),
		  "d" (a1),
		  "c" (a2),
		  "b" (a3),
		  "D" (a4),
		  "S" (a5)
		: "cc", "memory");
	
	if(check && ret > 0)
		panic("syscall %d returned %d (> 0)", num, ret);

	return ret;
}