Truncate procedure unable to work under Linux, is this a bug? This code is unable to work under linux: the Truncate drops an error message if the file is larger than 2 or 3 GB.
I tested it with Free Pascal 2.6.4 under Debian Jessie 64 bit. It produce the same error message under Ubuntu 12.04 32 bit with Free Pascal 2.4.4
Sometimes I did not get any error message but the file (which was 2 or 3 GB) will be only some hundred MB after truncate... It operates correctly under Windows.

It produce the following error message:
An unhandled exception occurred at $<address>:
EPrivilege : Privileged instruction
$<address>

Program File_Trunc;
{$MODE OBJFPC} {$H+}
uses dos,sysutils;
var
	f : file of byte;
	fs : int64;
begin
	assign(f,paramstr(1));
	ReSet(f);
	fs := FileSize(f);
	WriteLn('Original file size: ',fs);
	fs := fs-3456789;
	WriteLn('File size after truncate: ',fs);
	Seek(f,fs);
	Truncate(f);
	Close(f);
end.
Best regards, Geza

Truncate is a leftover from the DOS days.
It does not work with files >2 Gb, the file position is 32-bit.

There is the Filetruncate function from sysutils:

Function FileTruncate (Handle: THandle; Size: Int64) : boolean;

but even that does not work with files >2Gb on unix, because the underlying system call does not support it. I don't know what happens on Windows.

Michael.

Michael Van Canneyt wrote

Function FileTruncate (Handle: THandle; Size: Int64) : boolean; but even that does not work with files >2Gb on unix, because the underlying system call does not support it. I don't know what happens on Windows.

On windows it should be possible, at least no restriction mentioned in https://msdn.microsoft.com/en-us/library/windows/desktop/aa365531%28v=vs.85%29.aspx

Hi,
It should work if Truncate64 is used instead of Truncate. I suggest its a bug, albeit probably a wishlist one.

http://man7.org/linux/man-pages/man2/ftruncate.2.html

Regards,
Peter

In our previous episode, Peter said:

It should work if Truncate64 is used instead of Truncate. I suggest its a bug, albeit probably a wishlist one. http://man7.org/linux/man-pages/man2/ftruncate.2.html

ftruncate64 is already used for 32-bit CPUs, ftruncate for 64-bit cpus

You can get info on what FPC sends to the kernel using strace.

Thanks for that. So is it a bug then? Why is 64-bit not using ftruncate64?

Regards,
PB.

In our previous episode, Peter said:

> Thanks for that. So is it a bug then? Why is 64-bit not using ftruncate64?

I'm no linux expert, but I assume because it is only for 32-bit. On 64-bit, off_t already is 64-bit, so the posix template matches 1:1, and there is no need for another function.

Most BSDs have off_t at 64-bit, and therefore don't have this problem.

It is a bug in the system unit. I committed a patch in rev. 30892.

Michael.