specific bug in load directive

Index > Compiler Internals > specific bug in load directive

Author

Thread

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 12 Oct 2012, 15:07

He is only appearing under pure DOS and only with dos version of fasm.

Code:

macro LoadTest Name
{
  virtual at 0
  NameStart::
    db Name
  Length = $
  end virtual
  repeat Length
    load LETTER byte from NameStart:(%-1)
  end repeat
}
        LoadTest "String"

Code:

flat assembler  version 1.71.04  (3283967 kilobytes memory)
A.ASM [12]:
        LoadTest "String"
A.ASM [9] LoadTest [7]:
    load LETTER byte from NameStart:(%-1)
error: value out of range.

_________________
smaller is better

12 Oct 2012, 15:07

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 12 Oct 2012, 16:45

By "pure" do you mean real mode (without DPMI)? Does the bug disappear if you force it to run with DPMI (for example by installing EMM386 and DPMI driver)?

12 Oct 2012, 16:45

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 12 Oct 2012, 17:16

DPMI may be present or not.

12 Oct 2012, 17:16

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 12 Oct 2012, 17:24

Even if DPMI is present, but you are still in real mode, not V86, fasm will use the real mode instead. Have you tried in V86 mode too? Is FASMD affected by the same bug?

And what version of DOS is it?

12 Oct 2012, 17:24

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 12 Oct 2012, 19:30

I tested it with HDPMI32 and JEMM386, MS-DOS version 7.10.
FASMD is not affected this bug.

12 Oct 2012, 19:30

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 15 Oct 2012, 07:43

So far I tested it under MS-DOS 6.22, but I was unable to reproduce the bug. Do you think it's specific to that DOS version, or perhaps it's related to some other factors?

15 Oct 2012, 07:43

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 15 Oct 2012, 13:01

In dos I have 3.2 GB of the free memory. The bug is caused by it.
After starting fasm in with parameter "-m1024", everything is all right.

Code:

      data_address_type_ok:
        mov     ebx,edi
        xor     ecx,ecx
        add     ebx,eax
        adc     ecx,edx
        jnz     bad_data_address        ;<- BUG in this line
        mov     eax,ebx
        sub     eax,[ds:ebp+18h]
        jc      bad_data_address
        movzx   ecx,[operand_size]
        add     eax,ecx
        cmp     eax,[ds:ebp+1Ch]
        ja      bad_data_address
        clc
        ret

I tested it with my debugger in unreal mode.

_________________
smaller is better

Last edited by CandyMan on 15 Oct 2012, 19:00; edited 1 time in total

15 Oct 2012, 13:01

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 15 Oct 2012, 13:17

Thank you, now I see where the problem is. The DOS reference was in fact a bit misleading, since it made me test the problem on machine with 24 MB of memory. Very Happy

15 Oct 2012, 13:17

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 15 Oct 2012, 16:51

Please try it know and let me know if this fixes the problem.

15 Oct 2012, 16:51

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 15 Oct 2012, 19:28

The bug still is appearing.

15 Oct 2012, 19:28

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 15 Oct 2012, 21:46

And now?

15 Oct 2012, 21:46

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 16 Oct 2012, 06:16

Now he is acting.
Thanks.

16 Oct 2012, 06:16

< Last Thread | Next Thread >

Forum Rules:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum