On 08/13/2010 10:52 AM, Mike Frysinger wrote:
On Thu, Aug 12, 2010 at 10:40 PM, Thomas Chou wrote:
The "Nios II Processor Reference Handbook" said, "call can transfer execution anywhere within the 256 MByte range determined by PC31..28. The Nios II GNU linker does not automatically handle cases in which the address is out of this range."
So we have to use registered "callr" instruction to do the job.
doesnt NIOS have an insn to call indirectly via a register ? typically that's how function pointers should be handled when gcc generates code. -mike
Hi Mike,
The nios2 does have "callr" instruction to do registered call. But the nios2 gcc didn't generate correct code when the reset vector is passed as a constant. It just generated a direct "call", which was wrong when the reset vector was not located in the same 256MB span as u-boot. The gcc does generate correct "callr" if the reset vector is passed as an argument. As Altera said, this is a limitation (or bug?) of nios2 toolchain.
So I'd take a similar inline asm approach as we do in linux kernel.
Best regards, Thomas