Re: [PATCH] symbol: fix offset print for function pointers that return pointers

[lijiang <lijiang@xxxxxxxxxx>]

在 2021年04月02日 15:02, HAGIO KAZUHITO(萩尾　一仁) 写道:
> -----Original Message-----
>> In the show_member_offset() function, when trying to handle function
>> pointers, the case for "(*" is handled.  However, if the function
>> pointer returns a pointer or a pointer to a pointer, then the
>> condition is unhandled.  This results in the offset not being printed.
>>
>> Fix by first checking if the member is potentially a function pointer,
>> then checking if it returns a pointer or a pointer to a pointer.
>>
>> Signed-off-by: John Pittman <jpittman@xxxxxxxxxx>
> 
> Good catch... I've confirmed that the patch works as expected with RHEL7's
> struct offload_callbacks:
> 
> crash> struct -o offload_callbacks
> struct offload_callbacks {
>    [0] struct sk_buff *(*gso_segment)(struct sk_buff *, netdev_features_t);
>    [8] struct sk_buff **(*gro_receive)(struct sk_buff **, struct sk_buff *);
>   [16] int (*gro_complete)(struct sk_buff *, int);
> }
> SIZE: 24

This should be a good example for the case described in patch log. But I didn't
reproduce it on rhel7 before applying this patch, it's strange. 
...
      KERNEL: /usr/lib/debug/lib/modules/3.10.0-1160.24.1.el7.x86_64/vmlinux
...
     RELEASE: 3.10.0-1160.24.1.el7.x86_64
     VERSION: #1 SMP Thu Mar 25 21:21:56 UTC 2021
     MACHINE: x86_64  (2892 Mhz)
      MEMORY: 4 GB
         PID: 7815
     COMMAND: "crash"
        TASK: ffffa10210512100  [THREAD_INFO: ffffa10189b34000]
         CPU: 1
       STATE: TASK_RUNNING (ACTIVE)

crash> struct -o offload_callbacks
struct offload_callbacks {
       struct sk_buff *(*gso_segment)(struct sk_buff *, netdev_features_t);
       struct sk_buff **(*gro_receive)(struct sk_buff **, struct sk_buff *);
  [16] int (*gro_complete)(struct sk_buff *, int);
}
SIZE: 24

Do you happen to know how to reproduce this issue? John Pittman.

Thanks.
Lianbo

> 
> Acked-by: Kazuhito Hagio <k-hagio-ab@xxxxxxx>
> 
> Thanks,
> Kazu
> 
>> ---
>>  symbols.c | 11 +++++++++--
>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/symbols.c b/symbols.c
>> index a2d5c6c..5d7da6e 100644
>> --- a/symbols.c
>> +++ b/symbols.c
>> @@ -8356,8 +8356,15 @@ show_member_offset(FILE *ofp, struct datatype_member *dm, char *inbuf)
>>  		}
>>  	} else if (c) {
>>  		for (i = 0; i < c; i++) {
>> -			if (STRNEQ(arglist[i], "(*")) {
>> -				target = arglist[i]+2;
>> +			if (strstr(inbuf, "(*")) {
>> +				if (STRNEQ(arglist[i], "(*"))
>> +					target = arglist[i]+2;
>> +				else if (STRNEQ(arglist[i], "*(*"))
>> +					target = arglist[i]+3;
>> +				else if (STRNEQ(arglist[i], "**(*"))
>> +					target = arglist[i]+4;
>> +				else
>> +					continue;
>>  				if (!(t1 = strstr(target, ")")))
>>  					continue;
>>  				*t1 = NULLCHAR;
>> --
>> 2.17.2
> 

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