[Crash-utility] [PATCH] add -s option for struct command

[qiaonuohan]

At 2012-4-18 21:21, Dave Anderson wrote:
> In our original discussions, i thought that I had made it clear that
> the introduction of a new option paradigm with submembers could be
> avoided by using, for example, "page._mapcounter" instead of having
> to enter "page._mapcount.counter"?  This option makes the struct
> command seemingly violate its own rules, and really confuses things.
> For example, with your patch, a user would see things like this:

The most important reason why I insisted this option is the performance. 
Both original struct and print command are very slow. When kernel 
debugger wants to parse a bit amount of data, the performance of 
original struct and print command is not ideal.

>
>   crash>  page._mapcount.counter ffffea0000000508 -s
>   -1
>   crash>  page._mapcount.counter ffffea0000000508
>   struct: invalid format: page._mapcount.counter
>   crash>  page._mapcount ffffea0000000508
>       _mapcount = {
>         counter = -1
>       }
>   crash>  page._mapcount ffffea0000000508 -s
>   struct: invalid data structure reference page._mapcount
>   crash>

An idea of solving this confusion is changing the error information. 
When users uses "-s" option and error happens, error information 
suggests to use struct command without "-s" option if it is valid. And 
vice versa, when error happens without specified "-s" option.

>
> I had suggested that you look into the get_member_data() function
> in to the gdb/symtab.c file to access the member offset and size
> values.

Actually, the function need to be changed a lot to support what I want. 
I need the information of submember, and I need the position and size of 
bitfield. After investigation, function print_command_1 hides the data 
that I want. I know it is not a good idea of modifying this function. 
But what if a new function which has the similar mechanism with function 
print_command_1?

>
> I also don't like the idea of modifying the prototype of
> the stalwart print_command_1() gdb function, and the creation
> of a new gdb command.  Whenever there is a need to update the
> embedded gdb version, patches like this can be problematic.
> I would prefer that you create a new "GNU_XXXX" #define,
> similar to GNU_GET_SYMBOL_TYPE, pass the request through
> the gdb_command_funnel switch statement, and write a new
> standalone function to accomplish what you have done in the
> print_command_1() function.


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Regards
Qiao Nuohan