Re: [Qemu-devel] [PATCH v9 11/15] target-or32: Add system instructions

[Blue Swirl]

On Sat, Jul 14, 2012 at 2:08 PM, Jia Liu <address@hidden> wrote:
> Hi Max
>
> On Sat, Jul 14, 2012 at 9:49 PM, Max Filippov <address@hidden> wrote:
>>>> I don't think so, please check for example target-ppc/translate.c:4192
>>>> on how supervisor only mfsr is handled there.
>>>>
>>>
>>> Thank you for comment, Blue.
>>>
>>> is this code OK?
>>
>> Shouldn't there also be an exception in softmmu mode
>> if the CPU is not in supervisor mode?
>>
>
> Sorry, I...
> May you give me more comment? I'm not sure about this.

If a user tries to execute a supervisor instruction (only allowed for
kernel level code, not applications), the instruction won't be
executed but an exception will be raised.

This is the PPC mfsr instruction part of target-ppc/translate.c:
/* mfsr */
static void gen_mfsr(DisasContext *ctx)
{
#if defined(CONFIG_USER_ONLY)
    gen_inval_exception(ctx, POWERPC_EXCP_PRIV_REG);
#else
    TCGv t0;
    if (unlikely(!ctx->mem_idx)) {

Here the MMU mode is checked for user mode. I'd use more explicit
check ctx->mmu_idx == MMU_USER_IDX.

        gen_inval_exception(ctx, POWERPC_EXCP_PRIV_REG);
        return;
    }
    t0 = tcg_const_tl(SR(ctx->opcode));
    gen_helper_load_sr(cpu_gpr[rD(ctx->opcode)], cpu_env, t0);
    tcg_temp_free(t0);
#endif
}

>
>>>
>>>     case 0x2d:    /* l.mfspr */
>>>         LOG_DIS("l.mfspr r%d, r%d, %d\n", rd, ra, I16);
>>>         {
>>> #if defined(CONFIG_USER_ONLY)
>>>             gen_illegal_exception(dc);
>>> #else
>>>             TCGv_i32 ti = tcg_const_i32(I16);
>>>             gen_helper_mfspr(cpu_R[rd], cpu_env, cpu_R[rd], cpu_R[ra], ti);
>>>             tcg_temp_free_i32(ti);
>>> #endif
>>>         }
>>>         break;
>>>
>>>     case 0x30:    /* l.mtspr */
>>>         LOG_DIS("l.mtspr %d, r%d, r%d, %d\n", I5, ra, rb, I11);
>>>         {
>>> #if defined(CONFIG_USER_ONLY)
>>>             gen_illegal_exception(dc);
>>> #else
>>>             TCGv_i32 im = tcg_const_i32(tmp);
>>>             gen_helper_mtspr(cpu_env, cpu_R[ra], cpu_R[rb], im);
>>>             tcg_temp_free_i32(im);
>>> #endif
>>>         }
>>>         break;
>>>
>>
>> --
>> Thanks.
>> -- Max
>
> Regards,
> Jia.