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

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

On 5/11/2021 2:59 AM, Wang, Haiyue wrote:
>> -----Original Message-----
>> From: Yigit, Ferruh <ferruh.yigit@intel.com>
>> Sent: Tuesday, May 11, 2021 01:28
>> To: Wang, Haiyue <haiyue.wang@intel.com>; 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: dev@dpdk.org; stable@dpdk.org; Kevin Traynor <ktraynor@redhat.com>; Ajit Khaparde
>> <ajit.khaparde@broadcom.com>
>> Subject: Re: [dpdk-dev] [PATCH 3/4] net/ice/base: fix build with gcc11
>>
>> 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.
>>
> 
> That's why they are static function, not API. These functions are designed for
> internally using to handle the compact memory layout with different types.
> 
> These XXX_SIZE is a helper to get the different memory type size. Of course,
> this should be very careful, in other words, as you said: follows a contract. ;-)
> 

As said above the code is logically correct (at least as far as I can see), but
it can be dangerous from programming perspective.

> 
> #define DUMMY_ETH_HDR_LEN               16
> #define ICE_SW_RULE_RX_TX_ETH_HDR_SIZE \
>         (offsetof(struct ice_aqc_sw_rules_elem, pdata.lkup_tx_rx.hdr) + \
>          (DUMMY_ETH_HDR_LEN * \
>           sizeof(((struct ice_sw_rule_lkup_rx_tx *)0)->hdr[0])))
> #define ICE_SW_RULE_RX_TX_NO_HDR_SIZE \
>         (offsetof(struct ice_aqc_sw_rules_elem, pdata.lkup_tx_rx.hdr))
> #define ICE_SW_RULE_LG_ACT_SIZE(n) \
>         (offsetof(struct ice_aqc_sw_rules_elem, pdata.lg_act.act) + \
>          ((n) * sizeof(((struct ice_sw_rule_lg_act *)0)->act[0])))
> #define ICE_SW_RULE_VSI_LIST_SIZE(n) \
>         (offsetof(struct ice_aqc_sw_rules_elem, pdata.vsi_list.vsi) + \
>          ((n) * sizeof(((struct ice_sw_rule_vsi_list *)0)->vsi[0])))
> 
> 
> 
>>
>>
>