Re: [dpdk-dev] [PATCH 3/4] net/ice/base: fix build with gcc11

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 5/10/2021 6:04 PM, Wang, Haiyue wrote:
>> -----Original Message-----
>> From: dev <dev-bounces@dpdk.org> On Behalf Of Ferruh Yigit
>> Sent: Monday, May 10, 2021 23:03
>> To: Yang, Qiming <qiming.yang@intel.com>; Zhang, Qi Z <qi.z.zhang@intel.com>; Stillwell Jr, Paul M
>> <paul.m.stillwell.jr@intel.com>; Lu, Wenzhuo <wenzhuo.lu@intel.com>; Rong, Leyi <leyi.rong@intel.com>;
>> Shukla, Shivanshu <shivanshu.shukla@intel.com>
>> Cc: Yigit, Ferruh <ferruh.yigit@intel.com>; dev@dpdk.org; stable@dpdk.org; Kevin Traynor
>> <ktraynor@redhat.com>; Ajit Khaparde <ajit.khaparde@broadcom.com>
>> Subject: [dpdk-dev] [PATCH 3/4] net/ice/base: fix build with gcc11
>>
>> Reproduced with '--buildtype=debugoptimized' config,
>> compiler version: gcc (GCC) 12.0.0 20210509 (experimental)
>>
>> There are multiple build errors, like:
>> ../drivers/net/ice/base/ice_switch.c: In function ‘ice_add_marker_act’:
>> ../drivers/net/ice/base/ice_switch.c:3727:15:
>>       warning: array subscript ‘struct ice_aqc_sw_rules_elem[0]’
>>       is partly outside array bounds of ‘unsigned char[52]’
>>       [-Warray-bounds]
>>  3727 |         lg_act->type = CPU_TO_LE16(ICE_AQC_SW_RULES_T_LG_ACT);
>>       |               ^~
>> In file included from ../drivers/net/ice/base/ice_type.h:52,
>>                  from ../drivers/net/ice/base/ice_common.h:8,
>>                  from ../drivers/net/ice/base/ice_switch.h:8,
>>                  from ../drivers/net/ice/base/ice_switch.c:5:
>> ../drivers/net/ice/base/ice_osdep.h:209:29:
>>       note: referencing an object of size 52 allocated by ‘rte_zmalloc’
>>   209 | #define ice_malloc(h, s)    rte_zmalloc(NULL, s, 0)
>>       |                             ^~~~~~~~~~~~~~~~~~~~~~~
>> ../drivers/net/ice/base/ice_switch.c:3720:50:
>>       note: in expansion of macro ‘ice_malloc’
>>   lg_act = (struct ice_aqc_sw_rules_elem *)ice_malloc(hw, rules_size);
>>
>> These errors are mainly because allocated memory is cast to
>> "struct ice_aqc_sw_rules_elem *" but allocated size is less than the size
>> of "struct ice_aqc_sw_rules_elem".
>>
>> "struct ice_aqc_sw_rules_elem" has multiple other structs has unions,
>> based on which one is used allocated memory being less than the size of
>> "struct ice_aqc_sw_rules_elem" is logically correct but compiler is
>> complaining about it.
>>
>> As a solution making sure allocated memory size is at least size of
>> "struct ice_aqc_sw_rules_elem".
>> The function to use the struct is 'ice_aq_sw_rules()', and it already has
>> parameter for size of the rule, allocating more than needed shouldn't
>> cause any problem.
>>
>> Fixes: c7dd15931183 ("net/ice/base: add virtual switch code")
>> Fixes: 02acdce2f553 ("net/ice/base: add MAC filter with marker and counter")
>> Fixes: f89aa3affa9e ("net/ice/base: support removing advanced rule")
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
>> ---
>> Cc: paul.m.stillwell.jr@intel.com
>> Cc: qi.z.zhang@intel.com
>> Cc: leyi.rong@intel.com
>> Cc: Kevin Traynor <ktraynor@redhat.com>
>> Cc: Ajit Khaparde <ajit.khaparde@broadcom.com>
>> ---
>>  drivers/net/ice/base/ice_switch.c | 30 +++++++++++++++++++++++-------
>>  1 file changed, 23 insertions(+), 7 deletions(-)
> 
> GCC bug ?
> 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98266
> 
> Bug 98266 - [11 Regression] bogus array subscript is partly outside array bounds on virtual inheritance
> 

I am not sure if this is a gcc defect.

Here there is a memory allocated and assigned to "struct ice_aqc_sw_rules_elem
*", but allocated memory size is less than the struct size. As far as I
understand this is the reason of compiler warning.

For this case it may not be problem logically since both who allocates memory
and who uses the memory follows a contract, but there is a mismatch between
pointer type and object. If some other function wants to access all fields of
the struct, it will be out of bound access.