Re: [PATCH 2/2] remote.c, QCatchSyscalls: Build std::string instead of unique_xmalloc_ptr (Re: [RFA 4/6] Simple cleanup removals in remote.c)

[Pedro Alves <palves@redhat.com>]

On 10/19/2017 04:17 AM, Simon Marchi wrote:
> On 2017-10-16 19:38, Pedro Alves wrote:
>> diff --git a/gdb/remote.c b/gdb/remote.c
>> index 6b77a9f..a6cb724 100644
>> --- a/gdb/remote.c
>> +++ b/gdb/remote.c
>> @@ -2086,40 +2086,32 @@ remote_set_syscall_catchpoint (struct
>> target_ops *self,
>>                pid, needed, any_count, n_sysno);
>>      }
>>
>> -  gdb::unique_xmalloc_ptr<char> built_packet;
>> +  std::string built_packet;
>>    if (needed)
>>      {
>>        /* Prepare a packet with the sysno list, assuming max 8+1
>>       characters for a sysno.  If the resulting packet size is too
>>       big, fallback on the non-selective packet.  */
>>        const int maxpktsz = strlen ("QCatchSyscalls:1") + n_sysno * 9
>> + 1;
>> -
>> -      built_packet.reset ((char *) xmalloc (maxpktsz));
>> -      strcpy (built_packet.get (), "QCatchSyscalls:1");
>> +      built_packet.reserve (maxpktsz);
>> +      built_packet = "QCatchSyscalls:1";
>>        if (!any_count)
>>      {
>> -      int i;
>> -      char *p;
>> -
>> -      p = built_packet.get ();
>> -      p += strlen (p);
>> -
>>        /* Add in catch_packet each syscall to be caught (table[i] !=
>> 0).  */
>> -      for (i = 0; i < table_size; i++)
>> +      for (int i = 0; i < table_size; i++)
>>          {
>>            if (table[i] != 0)
>> -        p += xsnprintf (p, built_packet.get () + maxpktsz - p,
>> -                ";%x", i);
>> +        string_appendf (built_packet, ";%x", i);
>>          }
>>      }
>> -      if (strlen (built_packet.get ()) > get_remote_packet_size ())
>> +      if (built_packet.size () > get_remote_packet_size ())
>>      {
>>        /* catch_packet too big.  Fallback to less efficient
>>           non selective mode, with GDB doing the filtering.  */
>>        catch_packet = "QCatchSyscalls:1";
>>      }
>>        else
>> -    catch_packet = built_packet.get ();
>> +    catch_packet = built_packet.c_str ();
> 
> You can get rid of built_packet, and make catch_packet the std::string. 
> And then this last else branch can be removed.

The reason I didn't do that is because that'd introduce an
allocation + one deep string copy in the '!needed' case:

  else
    catch_packet = "QCatchSyscalls:0";

when it's very easy to avoid.

So I pushed the patch in as is.

Thanks,
Pedro Alves