Re: [PATCH] Avoid harmful fall throughs in core_target::xfer_partial.

[John Baldwin <jhb@FreeBSD.org>]

On 3/17/22 9:06 AM, Pedro Alves wrote:
> On 2022-03-16 19:36, John Baldwin wrote:
>> The cases for TARGET_OBJECT_LIBRARIES and TARGET_OBJECT_LIBRARIES_AIX
>> can try to fetch different data objects (such as
>> TARGET_OBJECT_SIGNAL_INFO) if gdbarch methods for the requested data
>> aren't present.  Replace case fallthroughs with an explicit goto to
>> the default case.
> 
> This is OK.  I mean, I think it would be reasonable to instead return
> TARGET_XFER_E_IO -- it's what the other cases do (notice even TARGET_OBJECT_SIGNAL_INFO
> doesn't fallback to the beneath target if there's no gdbarch method installed), and the targets
> beneath (file and dummy) won't be returning any library anyhow.  OTOH, maybe some day we will
> teach GDB to read the list of libraries the program is linked with and load those before
> the program starts, and it's conceivable that we would do that at the file_stratum layer.

I'm happy to do whichever.  I was trying to preserve the intent from when
TARGET_OBJECT_LIBRARIES was first added.  If there are no beneath targets that
handle these objects, then I think it probably is cleaner to just fail with
TARGET_XFER_E_IO for now and let explicit fall through logic be added in the
future when it is needed.

> Pedro Alves
> 
>> ---
>>   gdb/corelow.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/gdb/corelow.c b/gdb/corelow.c
>> index 1579e6bc2b8..f7f2bd3f318 100644
>> --- a/gdb/corelow.c
>> +++ b/gdb/corelow.c
>> @@ -943,7 +943,7 @@ core_target::xfer_partial (enum target_object object, const char *annex,
>>   		return TARGET_XFER_OK;
>>   	    }
>>   	}
>> -      /* FALL THROUGH */
>> +      goto fallthrough;
>>   
>>       case TARGET_OBJECT_LIBRARIES_AIX:
>>         if (m_core_gdbarch != nullptr
>> @@ -964,7 +964,7 @@ core_target::xfer_partial (enum target_object object, const char *annex,
>>   		return TARGET_XFER_OK;
>>   	    }
>>   	}
>> -      /* FALL THROUGH */
>> +      goto fallthrough;
>>   
>>       case TARGET_OBJECT_SIGNAL_INFO:
>>         if (readbuf)
>> @@ -988,6 +988,7 @@ core_target::xfer_partial (enum target_object object, const char *annex,
>>         return TARGET_XFER_E_IO;
>>   
>>       default:
>> +    fallthrough:
>>         return this->beneath ()->xfer_partial (object, annex, readbuf,
>>   					     writebuf, offset, len,
>>   					     xfered_len);
> 


-- 
John Baldwin