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Subject: Re: [Qemu-devel] [PATCH v8 1/4] Add moxie target code
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To: Anthony Green <green@moxielogic.com>
Cc: qemu-devel@nongnu.org

On 03/04/2013 04:29 AM, Anthony Green wrote:
> +void tlb_fill(CPUMoxieState *env, target_ulong addr, int is_write, int mmu_idx,
> +              uintptr_t retaddr)
> +{
> +    int ret;
> +
> +    ret = cpu_moxie_handle_mmu_fault(env, addr, is_write, mmu_idx);
> +    if (unlikely(ret)) {
> +        if (retaddr) {
> +            cpu_restore_state(env, retaddr);
> +        }
> +    }
> +    cpu_loop_exit(env);
> +}
> +
> +void helper_raise_exception(CPUMoxieState *env, uint32_t pc, int ex)
> +{
> +    env->exception_index = ex;
> +    /* Stash the exception type.  */
> +    env->sregs[2] = ex;
> +    /* Stash the address where the exception occurred.  */
> +    env->sregs[5] = pc;
> +    /* Jump the the exception handline routine.  */
> +    env->pc = env->sregs[1];
> +    cpu_loop_exit(env);
> +}

To be fixed later: The cpu_restore_state trick is not exclusive to memory
operations.  Any kind of runtime exception can use it.  Which means...

> +
> +uint32_t helper_div(CPUMoxieState *env, uint32_t pc, uint32_t a, uint32_t b)
> +{
> +    if (unlikely(b == 0)) {
> +        helper_raise_exception(env, pc, MOXIE_EX_DIV0);
> +        return 0;
> +    }

You need not store to or pass cpu_pc into the division routines.

> +DEF_HELPER_4(div, i32, env, i32, i32, i32)
> +DEF_HELPER_4(udiv, i32, env, i32, i32, i32)

Should use HELPER_FLAGS_4 with TCG_CALL_NO_WG, indicating that the function
does not write to tcg global registers.  (It does read them, via the exception
path.)


r~