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Thread: ASM includes broken in fpc 3.0.4 / x86_64

  1. #1

    ASM includes broken in fpc 3.0.4 / x86_64

    Wait. I'm now not sure it wasn't MY fault.
    x86_64 asm is a veritable minefield for someone who learned x86 asm during DOS times. So many instructions that compile, seem to work, but fail with addresses above 4Gb causing AVs or trashed memory.

    Will investigate in detail later.

    I will investigate it and fill a bug report later, got no time now.

    But the fact is, ASM includes are broken in this combination.
    Everything works fine for i686; the same ASM blocks work fine with fpc 2.6.4 so it's not my fault (probably).

    Example of code that silently trashes memory:

    function GetExceptionState(): PMotherSehState;
       Note: while it *can* allocate the block for a thread
       it knows nothing about, that is *not* a desired behavior.
       Thus, any thread better call this function beforehand,
       in the beginning of it's Execute method.
       There is Mother^.Core.AllocateThreadExceptionState for the module
      T: TThreadId;
      T:= GetCurrentThreadId();
      Result:= @Mother^.ExceptionState;
      while true do begin
        if Result^.ThreadId = T then begin
        if not Assigned(Result^.Next) then begin
          VerboseLog('  Allocating exception state for thread ID=' + IntToHex(T, 8) + 'h...');
          Result^.Next:= new(PMotherSehState);
          Result:= Result^.Next;
          FillChar(Result^, SizeOf(Result^), 0);
          Result^.ThreadId:= T;
          Result^.events[High(Result^.events)].eType:= deke_Terminator;
        {$ifdef CPUX86_64}
           {$if (FPC_FULLVERSION>20604) and (FPC_FULLVERSION<39999)}
             {$fatal This #@$# trashes memory. Use FPC 2.6.4 instead.}
            mov rsi, qword[Result]
            mov ax, ss
            mov word[rsi + TMotherSEHState.StackSegment], ax
          end['rax', 'rsi'];
        {$ifdef CPU386}
            mov esi, dword[Result]
            mov ax, ss
            mov word[esi + TMotherSEHState.StackSegment], ax
          end['eax', 'esi'];
        Result:= Result^.Next;
    -- it seems to work, then following exception processing crashes with "exception state not found for thread <ID>". Commenting the ASM block out fixes that.

      PMother = ^TMother;
      TMother = maybepacked record
        Safe: boolean;
        Validate: function(sizes: array of const): boolean; cdecl;
        SehCriticalSection: TRTLCriticalSection;
        State: TMotherState_;
        Core: TMotherCore;
          : TMotherSehState; //contains a pointer-chain of states for other threads
        CPU: TMotherCPU;
        Timer: TMotherTimer;
        Config: TMotherConfig;
        AssetKeeper: TMotherAssetKeeper;
        Memory: TMotherMemory;
        Stream: TMotherStream_;
        Module: TMotherModule_;
        GAPI: TMotherGAPI;
        Sound: TMotherSound;
        Text: TMotherText;
        Display: TMotherDisplay;
        Image: TMotherImaging;
    	  Input: TMotherInput_;
        Gamepad: TMotherGamepad;
        PenTablet: TMotherPenTablet;
        {$ifdef cgekernel}
         LockupGuard: TLockupGuard;
         stub1: ptruint;
        Debug: TMotherDebug;
        ReservedStub: array[0..10000] of ptruint;
      PMotherSehState = ^TMotherSEHState;
      TMotherSEHState = maybepacked record
        // see cge.ResetMotherErrorState() and cl_die.GetExceptionState()
        ThreadId: TThreadId;
        ExceptionCode, //true exception codes in Windows, not used in Linux (see
        ExceptionAddress: ptruint;
        StackFrameAddress: ptruint; //NOT used //used to restore rbp
        DyingAfterTrueException, {if the exception handling chain was set off
           by a real exception like an AV and not by a controlled call to Die() }
        IsModuleThread, {The current thread is created by the module and should be
          processed differently}
          : boolean;
        AbbrTitleForIndicator: ShortString3;
        StackSegment: Word;
        ThreadTitle: {$ifdef cgekernel} UnicodeString {$else} PUnicodeChar {$endif};
        AVMemoryOperation: ptruint; //0 - read, 1 - write, 8-Data Execution Prevention. See MSDN.
        //thread load details are stored here: I did not find a better place
        tlic: TThreadLoadKind;
        tlitsc: {$ifdef cpuarm} timeval {$else} qword {$endif};
        tli: array [TThreadLoadKind] of int64; //accumulates RDTSC cycles
        ReservedStub: array[0..3] of ptruint;
        Next: PMotherSehState;
        events: array[0..DyingEventsLimit] of TDyingEventRec; //approximately 60 kilobytes

      // arm on Raspberry Pi
      {$define maybepacked:=}
      {$packrecords 4}
      {$define maybepacked:=packed}
    Last edited by Chebmaster; 07-09-2018 at 07:52 AM.

  2. #2
    This Cheb is stumped.

    ; [37] Result^.events[High(Result^.events)].eType:= deke_Terminator;
    		mov	rax,qword ptr [rbp-8]
    ; Register raxreleased
    		mov	dword ptr [rax+59118],1
    ; Register raxallocated
    ; Register rsiallocated
    ; [43] mov rsi, qword[Result]
    		mov	rsi,qword ptr [rbp-8]
    ; [44] mov ax, ss
    		mov	ax,ss
    ; [45] mov word[rsi + TMotherSEHState.StackSegment], ax
    		mov	word ptr [rsi+60],ax
    ; Register raxreleased
    ; Register rsireleased
    ; Register raxallocated
    ; [56] LeaveCriticalsection(Mother^.SehCriticalSection);
    		mov	rax,qword ptr [U_CL_CGE_MOTHER+$]
    	movq	-8(%rbp),%rax
    	movl	$1,59118(%rax)
    	# Register rax released
    	# Register rax,rsi allocated
    # [43] mov rsi, qword[Result]
    	movq	-8(%rbp),%rsi
    # [44] mov ax, ss
    	movw	%ss,%ax
    # [45] mov word[rsi + TMotherSEHState.StackSegment], ax
    	movw	%ax,60(%rsi)
    	# Register rsi released
    	# Register rax allocated
    # [56] LeaveCriticalsection(Mother^.SehCriticalSection);
    	movq	U_$CL_CGE_$$_MOTHER(%rip),%rax
    These look the same to me.

  3. #3
    Did you figure it out? If you can glue together some test program that fails, I can take a look.

  4. #4
    Sorry, I delayed investigating this problem for much later, when I have 32-bit version of my engine running many real tasks without glitching or crashing.

    Add to that I install my own SEH handler for Win32, which I had to change to VEH handler for Win64...
    Add to that that I use pointer arithmetics in many places and had since weeded out several coding horrors via simple search for "cardinal" keyword...
    No, this was probably stupid me crying wolf because of trashed memory elsewhere

  5. #5
    No need to apologize, glad you managed to fix the issue - one sad panda less in the world

  6. #6
    PGDCE Developer de_jean_7777's Avatar
    Join Date
    Nov 2006
    Bosnia and Herzegovina (Herzegovina)
    Quote Originally Posted by Chebmaster View Post
    Too often this is the case for me too, where weird behavior is because I trashed memory due to the hacks I employ. A lot less of these nowadays, but still can cause a lot of hours wasted because of memory mismanagement
    In defeat we learn.

  7. #7
    So I've found *yet another* chunk of assembly code I botched porting from i386 to x86_64. Which compiles and works in 64-bit compatibility mode (all addresses limited to the lower 4Gb) that is only only generated using fpc 2.6.4 when you set debugging info to stabs) but trashes memory happily in true 64-bit addressing mode (because, as I was informed, most of MOV variations silently clip the address to its lower 32 bits unless the register you move to/from memory is RAX/EAX).
    Namely, instead of
            mov rax, [pes]
            mov rbx, rax
            mov rax, qword[rbx + TMotherSEHState.tlitsc]
            mov rcx, rax
            xor rax, rax
            shl rdx, 32
            or rax, rdx
            mov qword[rbx + TMotherSEHState.tlitsc], rax;
            sub rax, rcx
            mov rdx, rax
            xor rax, rax
            mov eax, dword[rbx + TMotherSEHState.tlic]
            mov ecx, eax
            mov rax, rdx
            add qword[rbx + rcx * 8 + TMotherSEHState.tli], rax
          end ['rax', 'rcx', 'rdx', 'rbx'];
    I had this heresy:
                mov rbx, [pes]
                mov rcx, qword[rbx + TMotherSEHState.tlitsc]
                mov eax, 0
                mov dword[rbx + TMotherSEHState.tlitsc], eax;
                mov dword[rbx + 4 + TMotherSEHState.tlitsc], edx;
                shl rdx, 32
                add rdx, rax
                sub rdx, rcx
                xor rcx, rcx
                mov ecx, dword[rbx + TMotherSEHState.tlic]
                add qword[rbx + rcx * 8 + TMotherSEHState.tli], rdx
    I hope this compiles and works when my project compiles again.

  8. #8
    Hi, did it work?

    TweakBox word counter Tutuapp
    Last edited by davido; 18-01-2020 at 07:47 PM.

  9. #9
    Cannot say yet because I froze working on both Linux and x86_64 until I finish rehauling both my ODBMS and GUI systems and get a perfectly working test using fpc 2.6.4 for Win32.
    Also, I need FPC 3.2 released before trying x86_64 again: 3.0.x is lacking some much needed features so I cannot debug using my tools.


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