[fasmg] windows lseek

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Mike Gonta

Joined: 26 Dec 2010
Posts: 243

Mike Gonta 25 May 2017, 21:56

Code:

invoke SetFilePointer, ebx, eax, [position_high], ecx

The third parameter to SetFilePointer should be a pointer to position_high or NULL.

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Mike Gonta
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25 May 2017, 21:56

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 25 May 2017, 22:06

Thank you for spotting this. It shows that I never tested it with really large files.

25 May 2017, 22:06

Mike Gonta

Joined: 26 Dec 2010
Posts: 243

Mike Gonta 26 May 2017, 12:16

Code:

lseek:
; in: ebx = file handle, cl = method, edx:eax = offset
; out: edx:eax = new offset from the beginning of file, cf set on error
; preserves: ebx, esi, edi
        movzx   ecx,cl
        mov     [position_high],edx
        invoke  SetFilePointer,ebx,eax,position_high,ecx
        cmp     eax,-1
        je      interface_error
        mov     edx,[position_high]
        clc
        retn

MSDN wrote:

If the return value is INVALID_SET_FILE_POINTER and if lpDistanceToMoveHigh is non-NULL, an application must call
GetLastError to determine whether or not the function has succeeded or failed.

SetFilePointerEx is similar to the Linux sys_llseek parameters and might be a better fit.

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Mike Gonta
look and see - many look but few see

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26 May 2017, 12:16

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 26 May 2017, 14:12

Good catch! Corrected, thank you again.

26 May 2017, 14:12

Mike Gonta

Joined: 26 Dec 2010
Posts: 243

Mike Gonta 26 May 2017, 14:34

With SetFilePointerEx it's similar to fasmg (Linux) lseek.

Code:

  position qd ?
lseek:
; in: ebx = file handle, cl = method, edx:eax = offset
; out: edx:eax = new offset from the beginning of file, cf set on error
; preserves: ebx, esi, edi
  movzx ecx,cl
  invoke SetFilePointerEx,ebx,eax,edx,position,ecx
  test eax,eax
  jz interface_error
  mov eax, [position]
  mov edx, [position+4]
  clc
  retn

_________________
Mike Gonta
look and see - many look but few see

https://mikegonta.com

26 May 2017, 14:34

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 26 May 2017, 14:51

I'm OK with SetFilePointer, it just needed these corrections.

26 May 2017, 14:51

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