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

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Jan 19, 2016 at 01:00:50PM +1100, Alexey Kardashevskiy wrote:
> 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.

Actually latest discussions with Sukadev and the RH licensing people
suggest we won't need that after all.  But still, point taken.

> 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().

Ok, that works for me.

> 
> 
> >+
> >+    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);
> 
> ?

Hm, ok.  I'm not entirely sold on the need, since most RTAS return
values are specific to individual RTAS calls, and they're not given
symbolic names by PAPR.  Still, why not.

> 
> 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...

For a minute I didn't see what you were getting at, then realized that
diagnostics_run_mode is in a different scope from the final store.

Yeah, that's not ok.

> 
> 
> 
> >+        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,
> >
> 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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