[fpc-devel] Constant arrays sometimes produce incorrect data tables

[Anton Tichawa]

David Butler wrote:

>Hi all
>
>I picked up this weird code generation problem (it was also present in
>2.0.0). I reported it as bug 4277 today. Unfortunately I can only
>reproduce it in a specific context, so please e-mail me for the unit.
>
>The problem is when you define an array of constant strings.
>
>For example:
>
>const
>  RFCMonthNames : Array[1..12] of String = (
>    'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
>    'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec');
>
>is usually assembled as something like:
>
>TC_P$TESTARRAY_RFCMONTHNAMES
>DD _$PROGRAM$_L4, _$PROGRAM$_L5, _$PROGRAM$_L6, _$PROGRAM$_L7, ......
>DD -1,3
>_$PROGRAM$_L4: DB "Jan",0 DD -1,3
>_$PROGRAM$_L5: DB "Feb",0 DD -1,3
>....
>
>which is correct, but the exact same code (in a different unit) is
>compiled differently, causing access violations when accessed:
>
>TC_CDATETIME_RFCMONTHNAMES
>DD _$CDATETIME$_L2046
>DD -1,3
>_$CDATETIME$_L2046:
>DB "Jan",0
>DD _$CDATETIME$_L2047
>DD -1,3
>_$CDATETIME$_L2047:
>DB "Feb",0
>DD _$CDATETIME$_L2048
>DD -1,3
>_$CDATETIME$_L2048:
>DB "Mar",0
>DD _$CDATETIME$_L2049
>DD -1,3
>_$CDATETIME$_L2049:
>DB "Apr",0
>........
>
>
>Regards
>David
>
>
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>
>  
>
There are two kinds of strings, shortstrings (max. 256 bytes) and 
ansistrings (any length, allocated on the heap). May be they're mixed, 
because the declaration "string" might use a shortstring in one unit, an 
ansistring in another, depending on compiler switches like "$H" or 
"$LONGSTRINGS".
Such mixing would very likely cause access violations. Try e. g. to 
change all declarations to "shortstring", which is enough for short 
month names.

hth,

Anton.