Re: [Qemu-devel] [PATCH v4 2/4] hw/core: rebase sysbus_get_fw_dev_path() to g_strdup_printf()

[Laszlo Ersek <lersek@redhat.com>]

On 06/15/15 16:23, Markus Armbruster wrote:
> Laszlo Ersek <lersek@redhat.com> writes:
> 
>> Cc: Markus Armbruster <armbru@redhat.com>
>> Cc: Marcel Apfelbaum <marcel@redhat.com>
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>> ---
>>
>> Notes:
>>     v4:
>>     - unchanged
>>     
>>     v3:
>>     - new in v3
>>
>>  hw/core/sysbus.c | 16 ++++++----------
>>  1 file changed, 6 insertions(+), 10 deletions(-)
>>
>> diff --git a/hw/core/sysbus.c b/hw/core/sysbus.c
>> index b53c351..0ebb4e2 100644
>> --- a/hw/core/sysbus.c
>> +++ b/hw/core/sysbus.c
>> @@ -281,19 +281,15 @@ static void sysbus_dev_print(Monitor *mon, DeviceState *dev, int indent)
>>  static char *sysbus_get_fw_dev_path(DeviceState *dev)
>>  {
>>      SysBusDevice *s = SYS_BUS_DEVICE(dev);
>> -    char path[40];
>> -    int off;
>> -
>> -    off = snprintf(path, sizeof(path), "%s", qdev_fw_name(dev));
>>  
>>      if (s->num_mmio) {
>> -        snprintf(path + off, sizeof(path) - off, "@"TARGET_FMT_plx,
>> -                 s->mmio[0].addr);
>> -    } else if (s->num_pio) {
>> -        snprintf(path + off, sizeof(path) - off, "@i%04x", s->pio[0]);
>> +        return g_strdup_printf("%s@"TARGET_FMT_plx, qdev_fw_name(dev),
> 
> I'd put a space between "%s@" and TARGET_FMT_plx.

I tried to copy the original format string very carefully, but you do
have a point. I'll do it in the next version.

> 
>> +                               s->mmio[0].addr);
>>      }
>> -
>> -    return g_strdup(path);
>> +    if (s->num_pio) {
>> +        return g_strdup_printf("%s@i%04x", qdev_fw_name(dev), s->pio[0]);
>> +    }
>> +    return g_strdup(qdev_fw_name(dev));
>>  }
>>  
>>  void sysbus_add_io(SysBusDevice *dev, hwaddr addr,
> 
> Would be nice if we didn't have to triplicate qdev_fw_name(), but I
> don't have better ideas.

Right, I could "cache it" in a local variable, but then I'd have to
triplicate the variable reference. And, runtime-wise, qdev_fw_name() is
called only once, it's just spelled out thrice in the source.

> 
> Bonus: no arbitrary length limit.  Before your patch, it's 39
> characters, and the code breaks catastrophically when qdev_fw_name() is
> longer: the second snprintf() is called with its first argument pointing
> beyond path[], and its second argument underflowing to a huge size.
> Textbook example of how not to use snprintf().  Worth mentioning in the
> commit message?

I was afraid that bashing on old code would only earn me some ire (not
from you, mind you -- in general), so I didn't mention this fact in the
commit message on purpose. :)

I will, in the next version.

> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> 

Thanks!
Laszlo