[M3devel] m3gap.... what is it and what does this mean?

[Rodney M. Bates]

Jay K wrote:
> Hey, look, until August, stock gdb never showed any fields!
> 
> The front does layout, it might tell the backend:
> 
> struct {
>   integer a at offset 4, size 4
>   integer b at offset 12, size 4
> }
> 
> in which case the backend will generate a "gap" field at offset 8, size 4
> 
> I suspect we might not have to generate the fields.
> I'm nervous that the backend might do its own layout and move up b to offset 8 otherwise.
> And there was other code in the backing doing similar.
> 
> We are in complete control of the name.
> If you want we can call it "_m3_padding_for_alignment"
> or "-m3_nothing_to_see_here"
> or "http://m3.org/faq1.html" (not sure they have to be valid C identifiers)

I doubt it, but they might need to be valid linker identifiers.  If there is a
character that is not legal in Modula-3 identifiers but legal here, it would be nice
to use it in generated things like this.  Then a debugger could normally suppress
displaying it, yet not be fooled by a Modula-3 programmer's actually declaring, e.g.,
_m3gap_8_56 in source code.  There are other places this comes up.

> 
>  - Jay
> 
> 
> 
> 
> ----------------------------------------
>> From: dragisha at m3w.org
>> To: m3devel at elegosoft.com
>> Date: Tue, 5 Oct 2010 15:32:30 +0200
>> Subject: [M3devel] m3gap.... what is it and what does this mean?
>>
>> (gdb) p event
>> $1 = {type = 8 '\b', _m3gap_8_56 = {}, window = 0x6924c0, send_event = 0 '\000', _m3gap_136_56 =
>> {}, time = 210453397504, state = 1, keyval = 0, length = 22953024, _m3gap_352_32 = {},
>> string = 0xa , hardware_keycode = 0, group = 0 '\000', _m3gap_472_40 = {}}
>>
>>
>> VAR
>> event: Gdk.EventKey;
>>
>> EventKey = RECORD
>> type: EventType;
>> window: WindowStar;
>> send_event: char;
>> time: unsigned_long_int;
>> state: unsigned_int;
>> keyval: unsigned_int;
>> length: int;
>> string: char_star;
>> hardware_keycode: unsigned_short_int;
>> group: unsigned_char;
>> END;
>>
>> also with m3gdb....
>>
>> (m3gdb) p event
>> $1 = {4type = 8 '\b', _m3gap_8_56 = {}, window = 0x0,
>> send_event = 0 '\000',
>> _m3gap_136_56 = {}, time = 49, state = -937844736,
>> keyval = 32616, length = 23801648,
>> _m3gap_352_32 = {}, string = 0x7f68c839be10 "\001
>> \000", hardware_keycode = 0, group = 0 '\000',
>> _m3gap_472_40 = {}}
>>
>> --
>> Dragiša Durić 
>>
>