BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Pierre, Is that error in BDS2006sp1?          BorlandTalk.com Forum Index -> Delphi Language BASM View previous topic :: View next topic   Author Message miab Guest Posted: Mon Mar 20, 2006 9:03 am    Post subject: Pierre, Is that error in BDS2006sp1? <cy> Posted By: pierre_le_riche Date: 2006-02-22 06:02 Summary: Critical Bugfix There was a bug that may cause an access violation inside the MoveX16L4 routine when reallocating a memory block under certain rare circumstances. Even if you have never encountered this bug, it is strongly recommended that you update to version 4.62 or later to prevent future trouble. It can only occur if the Align16Bytes option is disabled and the UseCustomVariableSizeMoveRoutines option is enabled. (Thanks to Jud Cole for tracking it down.) The symptom is an exception of the form "Access Violation: Invalid read of address XXXX0000" where XXXX is a non-zero number. It occurs on the line "mov eax, [eax + ecx + 8]" inside the MoveX16L4 routine. </cy> http://sourceforge.net/forum/forum.php?forum_id=543225 miab Back to top Pierre le Riche Guest Posted: Mon Mar 20, 2006 10:03 pm    Post subject: Re: Pierre, Is that error in BDS2006sp1? Hi miab, Quote: There was a bug that may cause an access violation inside the MoveX16L4 routine when reallocating a memory block under certain rare circumstances. Yes, but it has of course already been fixed for update 2 (which should be out soon). In the meantime the workaround is to force 16-byte alignment by calling "SetMinimumBlockAlignment(mba16Byte)" somewhere in your application's startup code. It's a rare bug, so unless you have actually seen a read access violation at address XXXX0000 (where XXXX is non-zero) I wouldn't worry about it too much. I certainly have never encountered the bug except in the manufactured test case, and the only encounter "in the wild" that I know of was in a memory manager test suite. Regards, Pierre Back to top Atmapuri Guest Posted: Tue Mar 21, 2006 9:03 am    Post subject: Re: Pierre, Is that error in BDS2006sp1? Hi! Quote: out soon). In the meantime the workaround is to force 16-byte alignment by calling "SetMinimumBlockAlignment(mba16Byte)" somewhere in your application's startup code. I thought that memory allocations were already 16byte alligned by default. What is the default byte allignment for arrays? 8 bytes? (len and ref fields have 4 bytes, together 8 and you cant allign to more than . Thanks! Atmapuri Back to top Pierre le Riche Guest Posted: Tue Mar 21, 2006 10:03 am    Post subject: Re: Pierre, Is that error in BDS2006sp1? Hi Atmapuri, Quote: I thought that memory allocations were already 16byte alligned by default. The default alignment is 8 bytes. Quote: What is the default byte allignment for arrays? 8 bytes? (len and ref fields have 4 bytes, together 8 and you cant allign to more than . Correct. 16 byte alignment is useful when you use SSE, but it doesn't help much other than that. Regards, Pierre Back to top Johan Nilsson Guest Posted: Wed Mar 22, 2006 8:03 am    Post subject: Re: Pierre, Is that error in BDS2006sp1? Quote: I certainly have never encountered the bug except in the manufactured test case, and the only encounter "in the wild" that I know of was in a memory manager test suite. Hi Pierre! I use XML-interfaces a lot, and I've been experiencing this bug a lot in one manufactured application. That application imports a lot of XML-documents. When I stress-test the application, the AV is raised at random, but always when less than 5 % of the imports are completed. After adding the SetMinimumBlockAlignment(mba16Byte); line, the AV is never raised. The address is always the same, but not on the format (XXXX0000) as you described. --------------------------- Debugger Exception Notification --------------------------- Project OrderImport.exe raised exception class EAccessViolation with message 'Access violation at address 00401DE5 in module 'OrderImport.exe'. Write of address 00000000'. --------------------------- Break Continue Help --------------------------- /Johan Back to top Pierre le Riche Guest Posted: Wed Mar 22, 2006 9:03 am    Post subject: Re: Pierre, Is that error in BDS2006sp1? Hi Johan, Quote: The address is always the same, but not on the format (XXXX0000) as you described. Project OrderImport.exe raised exception class EAccessViolation with message 'Access violation at address 00401DE5 in module 'OrderImport.exe'. Write of address 00000000'. The bug causes a *read* access violation, and always at a an address that is nonzero, but with zeroes in the last four digits. Your A/V is on a write and the address is zero, so it is not due to this bug. I can't explain why your application seems to work with 16 byte alignment but not 8 byte alignment. Regards, Pierre Back to top Johan Nilsson Guest Posted: Wed Mar 22, 2006 12:03 pm    Post subject: Re: Pierre, Is that error in BDS2006sp1? I should also add, that this isn't the original code, but code I've been testing on. Back to top Johan Nilsson Guest Posted: Wed Mar 22, 2006 12:03 pm    Post subject: Re: Pierre, Is that error in BDS2006sp1? You're right. It seems I'm responsible for the AV, when sharing data between apps. I never spent much time investigating it, since it's an old app, that uses the NexusDB-Memory Manager, where the AV never occures. The code below shows the problem, and one solution for it: var tCDS : TCopyDataStruct; tParam : string; tParamArray : array of Char; begin tParam := '64530;64791'; // Array-Buffer SetLength(tParamArray, Length(tParam) + 1); StrLCopy(PChar(tParamArray), PChar(tParam), Length(tParam)); tParamArray[Length(tParam) + 1] := #0; // CopyData tCDS.dwData := WM_MY_COPYID; tCDS.cbData := Length(tParam); // With this line it always works OK (and does not require anyArray-Buffer): // tCDS.lpData := PChar(tParam); // This line seems to be the cause to the AV. Though it never failes when using mba16Byte: tCDS.lpData := tParamArray; // SendMessage Result := SendMessage(AHandle, WM_COPYDATA, 0, LParam(@tCDS)); end; Changing the Arrar-Byffer to: SetLength(tParamArray, Length(tParam)); StrLCopy(PChar(tParamArray), PChar(tParam), Length(tParam)); or SetLength(tParamArray, Length(tParam) + 2); StrLCopy(PChar(tParamArray), PChar(tParam), Length(tParam)); tParamArray[Length(tParam) + 1] := #0; tParamArray[Length(tParam) + 2] := #0; also makes the AVs go away. /Johan Back to top Johan Nilsson Guest Posted: Wed Mar 22, 2006 4:03 pm    Post subject: Re: Pierre, Is that error in BDS2006sp1? Thanks! /Johan Back to top Pierre le Riche Guest Posted: Wed Mar 22, 2006 4:03 pm    Post subject: Re: Pierre, Is that error in BDS2006sp1? Hi Johan, Quote: // Array-Buffer SetLength(tParamArray, Length(tParam) + 1); StrLCopy(PChar(tParamArray), PChar(tParam), Length(tParam)); tParamArray[Length(tParam) + 1] := #0; There is a memory overwrite bug here. Dynamic array indexes are 0-based, so you are writing past the end of allocated memory. The last line should be: tParamArray[Length(tParam)] := #0; Quote: Changing the Arrar-Byffer to: SetLength(tParamArray, Length(tParam)); StrLCopy(PChar(tParamArray), PChar(tParam), Length(tParam)); This could also overwrite memory. You should allocate an extra byte for the trailing #0. Quote: SetLength(tParamArray, Length(tParam) + 2); StrLCopy(PChar(tParamArray), PChar(tParam), Length(tParam)); tParamArray[Length(tParam) + 1] := #0; tParamArray[Length(tParam) + 2] := #0; Same error. The last line overwrites memory. 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