Reported by Primoz Gabrijelcic, on Inprise's objectpascal newsgroup; checked by Stefan Hoffmeister; Tor-Arne Riksheim
Problem: EAccessViolation exception in perfectly bug-free program.
Applies to: All versions of Delphi 3, Delphi 4 and Delphi 5.
Workaround: none known
How to reproduce:
Compile and run following program with Delphi.
--------------- cut here ---------------
{$A+,B-,C-,D+,E-,F-,G+,H+,I+,J+,K-,L+,M-,N+,O-,P+,Q-,R+,S-,T-,U-,V+,W+,X+,Y-,Z1}
{$APPTYPE CONSOLE}
program Test502;
uses
Sysutils;
const
MAX = 3300;
var
f: text;
i: integer;
begin
Assign(f,'Test502a.dpr');
Rewrite(f);
Writeln(f,'{$A+,B-,C-,D+,E-,F-,G+,H+,I+,J+,K-,L+,M-,N+,O-,P+,Q-,R+,S-,T-,U-,
V+,W+,X+,Y-,Z1}');
Writeln(f,'program Test502a;');
Writeln(f,'uses Forms;');
Writeln(f,'var s: array [1..',MAX,'] of string;');
Writeln(f,'begin');
for i := 1 to MAX do
Writeln(f,' s[',i,'] := ''line ',i,''';');
Writeln(f,'end.');
Close(f);
end.
--------------- cut here ---------------
It will generate a test program, test.dpr, with a bunch of string assignment
statements in the form of
s[3282] := 'line 3282';
s[3283] := 'line 3283';
s[3284] := 'line 3284';
s[3285] := 'line 3285';
s[3286] := 'line 3286';
s[3287] := 'line 3287';
s[3288] := 'line 3288';
s[3289] := 'line 3289';
Open Test502a.dpr in Delphi, compile and run. You'll get an Access Violation
exception. In Delphi 3.02 exception occurs on line "s[3298] := 'line
3298';", in Delphi 4.0 + Update 1 it occures on the next line (s[3299] :=
...). A quick glance at code generated shows why (this example is from D
3.02):
s[3297] := 'line 3297';
mov eax,$0045cb64
mov edx,$00457830
call @LStrAsg
s[3298] := 'line 3298';
mov eax,$0045cb68
mov edx,$00447833 ; Here lies the bug!
call @LStrAsg
The address, moved into edx should be $00457833, which is exactly $10000
(64 kb!) off. Looks like in the depth of the Delphi compiler/linker there is still
some win16-pointer-related arithmetic which is not completely bulletproof.
Comment from Tor-Arne Riksheim:
I ran the test, and found that the error doesn't happen if the stringtable is
made of ShortStrings.
Jordan Russell:
In Delphi 6.0, the compiler now displays this error message: "Too many local constants. Use shorter procedures." |
