Re: [Qemu-devel] [PATCH 1/3] spapr: Small fixes to rtas_ibm_get_system_parameter, remove rtas_st_buffer

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 01/16/2016 12:14 PM, David Gibson wrote:
> rtas_st_buffer() appears in spapr.h as though it were a widely used helper,
> but in fact it is only used for saving data in a format used by
> rtas_ibm_get_system_parameter().  We can fold it into that caller just as
> simply.
>
> While we're there fix a couple of small defects in
> rtas_ibm_get_system_parameter:
>    - For the string value SPLPAR_CHARACTERISTICS, it wasn't including the
>      terminating \0 in the length which it should according to LoPAPR
>      7.3.16.1
>    - It now checks that the supplied buffer has at least enough space for
>      the length of the returned data, and returns an error if it does not.
>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>   hw/ppc/spapr_rtas.c    | 28 ++++++++++++++++++++--------
>   include/hw/ppc/spapr.h | 11 -----------
>   2 files changed, 20 insertions(+), 19 deletions(-)
>
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index 34b12a3..f4fb9ba 100644
> --- a/hw/ppc/spapr_rtas.c
> +++ b/hw/ppc/spapr_rtas.c
> @@ -235,9 +235,15 @@ static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
>                                             uint32_t nret, target_ulong rets)
>   {
>       target_ulong parameter = rtas_ld(args, 0);
> -    target_ulong buffer = rtas_ld(args, 1);
> +    target_ulong buffer = ppc64_phys_to_real(rtas_ld(args, 1));
>       target_ulong length = rtas_ld(args, 2);
> -    target_ulong ret = RTAS_OUT_SUCCESS;
> +    void *val;
> +    size_t vallen;

Having such temporary variables (val/vallen) tells me that a helper is a 
better solution as this assumes that one word and one buffer will be ever 
enough for all cases but there is already "7.3.16.17 Processor Module 
Information" coming (even though I have not heard from Sukadev for quite 
some time) which is more complicated that this.

May be rtas_st_buffer() is not the best name and it does not have to be 
global so I'd propose making it static and calling it syspar_st().


> +
> +    if (length < 2) {
> +        rtas_st(rets, 0, -9999); /* Parameter error */


#define RTAS_OUT_SYSPAR_PARAM_ERROR -9999
and then
rtas_st(rets, 0, RTAS_OUT_SYSPAR_PARAM_ERROR);

?

In all other places ("rtas_st(\S\+, 0") a macro is used (except just one 
case in spapr_pci.c which needs a fix).


> +        return;
> +    }
>
>       switch (parameter) {
>       case RTAS_SYSPARM_SPLPAR_CHARACTERISTICS: {
> @@ -249,24 +255,30 @@ static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
>                                             current_machine->ram_size / M_BYTE,
>                                             smp_cpus,
>                                             max_cpus);
> -        rtas_st_buffer(buffer, length, (uint8_t *)param_val, strlen(param_val));
> +        val = param_val;
> +        vallen = strlen(param_val) + 1;
>           g_free(param_val);
>           break;
>       }
>       case RTAS_SYSPARM_DIAGNOSTICS_RUN_MODE: {
> -        uint8_t param_val = DIAGNOSTICS_RUN_MODE_DISABLED;
> +        uint8_t diagnostics_run_mode = DIAGNOSTICS_RUN_MODE_DISABLED;
>
> -        rtas_st_buffer(buffer, length, &param_val, sizeof(param_val));
> +        val = &diagnostics_run_mode;


I know that any reasonable compiler will keep @diagnostics_run_mode on 
stack till return but it is still not clean...



> +        vallen = sizeof(diagnostics_run_mode);
>           break;
>       }
>       case RTAS_SYSPARM_UUID:
> -        rtas_st_buffer(buffer, length, qemu_uuid, (qemu_uuid_set ? 16 : 0));
> +        val = qemu_uuid;
> +        vallen = qemu_uuid_set ? 16 : 0;
>           break;
>       default:
> -        ret = RTAS_OUT_NOT_SUPPORTED;
> +        rtas_st(rets, 0, RTAS_OUT_NOT_SUPPORTED);
> +        return;
>       }
>
> -    rtas_st(rets, 0, ret);
> +    stw_be_phys(&address_space_memory, buffer, vallen);
> +    cpu_physical_memory_write(buffer + 2, val, MIN(vallen, length - 2));
> +    rtas_st(rets, 0, 0); /* Success */


rtas_st(rets, 0, RTAS_OUT_SUCCESS);



>   }
>
>   static void rtas_ibm_set_system_parameter(PowerPCCPU *cpu,
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 53af76a..ec9e7ea 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -513,17 +513,6 @@ static inline void rtas_st_buffer_direct(target_ulong phys,
>                                 MIN(buffer_len, phys_len));
>   }
>
> -static inline void rtas_st_buffer(target_ulong phys, target_ulong phys_len,
> -                                  uint8_t *buffer, uint16_t buffer_len)
> -{
> -    if (phys_len < 2) {
> -        return;
> -    }
> -    stw_be_phys(&address_space_memory,
> -                ppc64_phys_to_real(phys), buffer_len);
> -    rtas_st_buffer_direct(phys + 2, phys_len - 2, buffer, buffer_len);
> -}
> -
>   typedef void (*spapr_rtas_fn)(PowerPCCPU *cpu, sPAPRMachineState *sm,
>                                 uint32_t token,
>                                 uint32_t nargs, target_ulong args,
>


-- 
Alexey