Re: [PATCH] hw/core: Handle cpu_model_from_type() returning NULL value

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Gavin,

On 11/1/24 08:30, Gavin Shan wrote:
> Hi Phil,
> 
> On 1/11/24 16:47, Philippe Mathieu-Daudé wrote:
>> Per cpu_model_from_type() docstring (added in commit 445946f4dd):
>>
>>    * Returns: CPU model name or NULL if the CPU class doesn't exist
>>
>> We must check the return value in order to avoid surprises, i.e.:
>>
>>   $ qemu-system-arm -machine virt -cpu cortex-a9
>>    qemu-system-arm: Invalid CPU model: cortex-a9
>>    The valid models are: cortex-a7, cortex-a15, (null), (null), 
>> (null), (null), (null), (null), (null), (null), (null), (null), 
>> (null), max
>>
>> Add assertions when the call can not fail (because the CPU type
>> must be registered).
>>
>> Fixes: 5422d2a8fa ("machine: Print CPU model name instead of CPU type")
>> Reported-by: Peter Maydell <peter.maydell@linaro.org>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>> ---
>>   cpu-target.c          | 1 +
>>   hw/core/machine.c     | 5 +++++
>>   target/ppc/cpu_init.c | 1 +
>>   3 files changed, 7 insertions(+)
>>
>> diff --git a/cpu-target.c b/cpu-target.c
>> index 5eecd7ea2d..b0f6deb13b 100644
>> --- a/cpu-target.c
>> +++ b/cpu-target.c
>> @@ -291,6 +291,7 @@ static void cpu_list_entry(gpointer data, gpointer 
>> user_data)
>>       const char *typename = object_class_get_name(OBJECT_CLASS(data));
>>       g_autofree char *model = cpu_model_from_type(typename);
>> +    assert(model);
>>       if (cc->deprecation_note) {
>>           qemu_printf("  %s (deprecated)\n", model);
>>       } else {
>> diff --git a/hw/core/machine.c b/hw/core/machine.c
>> index fc239101f9..730ec10328 100644
>> --- a/hw/core/machine.c
>> +++ b/hw/core/machine.c
>> @@ -1422,16 +1422,21 @@ static bool is_cpu_type_supported(const 
>> MachineState *machine, Error **errp)
>>           /* The user specified CPU type isn't valid */
>>           if (!mc->valid_cpu_types[i]) {
>>               g_autofree char *requested = 
>> cpu_model_from_type(machine->cpu_type);
>> +            assert(requested);
>>               error_setg(errp, "Invalid CPU model: %s", requested);
>>               if (!mc->valid_cpu_types[1]) {
>>                   g_autofree char *model = cpu_model_from_type(
>>                                                    
>> mc->valid_cpu_types[0]);
>> +                assert(model);
>>                   error_append_hint(errp, "The only valid type is: 
>> %s\n", model);
>>               } else {
>>                   error_append_hint(errp, "The valid models are: ");
>>                   for (i = 0; mc->valid_cpu_types[i]; i++) {
>>                       g_autofree char *model = cpu_model_from_type(
>>                                                    
>> mc->valid_cpu_types[i]);
>> +                    if (!model) {
>> +                        continue;
>> +                    }
> 
> Shall we assert(model) for this case, to be consistent with other cases? :)

No, this is the "(null)" cases displayed in the example.

IOW, mc->valid_cpu_types[] contains a CPU type which isn't registered,
so we just skip it.

> 
>>                       error_append_hint(errp, "%s%s",
>>                                         model,
>>                                         mc->valid_cpu_types[i + 1] ? 
>> ", " : "");
> 
> Otherwise, the separator here need to be adjusted because it's uncertain 
> that
> mc->valid_cpu_types[i+1] ... mc->valid_cpu_types[END] are valid.

Here we know mc->valid_cpu_types[i] is *not* NULL, but
mc->valid_cpu_types[i + 1] might be (signaling the end
of the array).

This seems correct to me, but I might be missing something.

> 
>> diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c
>> index 344196a8ce..58f0c1e30e 100644
>> --- a/target/ppc/cpu_init.c
>> +++ b/target/ppc/cpu_init.c
>> @@ -7037,6 +7037,7 @@ static void ppc_cpu_list_entry(gpointer data, 
>> gpointer user_data)
>>       }
>>       name = cpu_model_from_type(typename);
>> +    assert(name);
>>       qemu_printf("PowerPC %-16s PVR %08x\n", name, pcc->pvr);
>>       for (i = 0; ppc_cpu_aliases[i].alias != NULL; i++) {
>>           PowerPCCPUAlias *alias = &ppc_cpu_aliases[i];
> 
> Thanks,
> Gavin
>