Re: [PATCH] displaying anonymous members of struct/union

qiaonuohan <qiaonuohan@xxxxxxxxxxxxxx> · Tue, 06 Mar 2012 17:14:06 +0800

At 2012-3-6 0:25, Dave Anderson wrote:

----- Original Message -----

Hello Dave,

I have realized the function to display anonymous members of
struct/union. There are three changes, which are listed below, and I
will take "struct page" for example.

1. anonymous members will be showed when using "struct page"

That's nice...

2. anonymous member, "struct page.private", will be showed together with
its offset

Sorry -- but doing that redefines the "struct" command output for both named
members and anonymous members.  The "struct -o" option should be used to prepend
the offset.  Can you re-work the patch so that it behaves the same way
as it currently does?

3. anonymous member with the address of the structure, "struct
page.private xxx", will be showed.

About the implementation, gdb code is changed, which is used to change
the output of the gdb command, "ptype ...". And function
"arg_to_datatype" is also modified to analyze anonymous member.

I'm presuming (but not sure) that the change to anon_member_offset() to use
open_tmpfile2() is because your patch introduces a new potential path to
anon_member_offset() that would be inside a open_tmpfile()/close_tmpfile()
region?  Is that correct?

Exactly, when showing struct.member, function do_datatype_declaration() 

is involved. And in this function, open_tmpfile() is called. Then after 

the call of open_tmpfile() and before the call of close_tmpfile(), 

show_member_offset(), in which I added ANON_MEMBER_OFFSET, is called. 

This macro will call anon_member_offset(). So I change to use 

open_tmpfile2() to prohibit to recursive usage.

The change to gdb's c_type_print_base() function is interesting -- do
you consider that a bug in gdb, or do you think they have a reason
for doing it the way it's done now?  I ask because gdb has several
structure-printing optional variables, so I'm kind of surprised that
it's hard-wired to behave the way it does.

The original gdb will display at most three levels of structure in depth 

when using command "ptype ..." without concerning the anonymous member. 

In my patch, I modified the calculation of "show", which is used to 

indicate the level. The show will not decrease 1, using my patch, when 

anonymous structure appears.

Take the below struct for example:

type = struct a {
    struct {
        struct {
            union {
                struct {
                ...
                };
                ...
            };
        };
    };
};

All will be displayed using my patch. And the original gdb will only 

display like:

type = struct a {
    struct {
        struct {...}
    };
};

The original gdb, in my opinion, shows simplicity. And comes to the 

aspect of source code, nothing obviously shows the differentiation. 

These are all that I can figure out until now.

Thanks,
   Dave

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--
--
Regards
Qiao Nuohan

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