Re: [Xen-devel] [PATCH 7/7] tools/kdd: mute spurious gcc warning

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 04/06/2018 09:07 AM, Wei Liu wrote:
> On Fri, Apr 06, 2018 at 08:39:53AM -0400, Boris Ostrovsky wrote:
>> On 04/04/2018 09:50 PM, Marek Marczykowski-Górecki wrote:
>>> gcc-8 complains:
>>>
>>>     kdd.c:698:13: error: 'memcpy' offset [-204, -717] is out of the bounds 
>>> [0, 216] of object 'ctrl' with type 'kdd_ctrl' {aka 'union <anonymous>'} 
>>> [-Werror=array-bounds]
>>>                  memcpy(buf, ((uint8_t *)&ctrl.c32) + offset, len);
>>>                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>     kdd.c: In function 'kdd_select_callback':
>>>     kdd.c:642:14: note: 'ctrl' declared here
>>>          kdd_ctrl ctrl;
>>>                   ^~~~
>>>
>>> But this is impossible - 'offset' is unsigned and correctly validated
>>> few lines before.
>>>
>>> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
>>> ---
>>>  tools/debugger/kdd/kdd.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/tools/debugger/kdd/kdd.c b/tools/debugger/kdd/kdd.c
>>> index 1bd5dd5..61d769e 100644
>>> --- a/tools/debugger/kdd/kdd.c
>>> +++ b/tools/debugger/kdd/kdd.c
>>> @@ -695,7 +695,10 @@ static void kdd_handle_read_ctrl(kdd_state *s)
>>>              KDD_LOG(s, "Request outside of known control space\n");
>>>              len = 0;
>>>          } else {
>>> +#pragma GCC diagnostic push
>>> +#pragma GCC diagnostic ignored "-Warray-bounds"
>>>              memcpy(buf, ((uint8_t *)&ctrl.c32) + offset, len);
>>> +#pragma GCC diagnostic pop
>>>          }
>>>      }
>>>  
>>
>> Breaks 32-bit build, at least with my (ancient, gcc version 4.4.5
>> 20101112 (Red Hat 4.4.5-2) (GCC)) compiler:
>>
>>
>>
>> kdd.c: In function ‘kdd_handle_read_ctrl’:
>> kdd.c:698: error: #pragma GCC diagnostic not allowed inside functions
>> kdd.c:699: error: #pragma GCC diagnostic not allowed inside functions
>> kdd.c:701: error: #pragma GCC diagnostic not allowed inside functions
>> make[5]: *** [kdd.o] Error 1
>>
> Does moving the relevant #pragma's outside of the function fix it?

The additional problem with these pragmas is that apparently push/pop
have been introduced in gcc 4.6.0:

https://gcc.gnu.org/onlinedocs/gcc-4.6.0/gcc/Diagnostic-Pragmas.html#Diagnostic-Pragmas

If you change release number to a lower one (e.g. 4.5.4) you won't see them.

So I can move "diagnostic ignored" from inside the function and that
will clear the "GCC diagnostic not allowed inside functions" error. But
then push/pop are not recognized:

cc1: warnings being treated as errors
kdd.c:639: error: expected [error|warning|ignored] after ‘#pragma GCC
diagnostic’
kdd.c:714: error: expected [error|warning|ignored] after ‘#pragma GCC
diagnostic’

(Interestingly, my 64-bit build completed without issues)

-boris

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