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Q57484: JMP Back More Than 128 Bytes Not Flagged

Article: Q57484
Product(s): See article
Version(s): 2.01
Operating System(s): MS-DOS
Keyword(s): ENDUSER | s_quickc buglist2.01 | mspl13_masm
Last Modified: 12-FEB-1990

The QuickC/QuickAssembler compiler Version 2.01 does not flag an
attempt to make a short jump backwards further than 128 bytes when one
pass assembly is enabled. The compiler produces an object file, but it
is erroneous. If incremental linking is enabled, the file will not
link properly and the following error message will be returned:

   SOURCE.OBJ (source.asm) : error L2002:  Fixup overflow at 1 in segment
   _TEXT : pos: 175 record type: 9C

If standard linking is enabled, the file will link, but the program
will not run properly.

One pass assembly is enabled by default, both inside and outside the
environment. Two pass assembly can be enabled by toggling the "One
Pass Assembly" switch inside the environment. It can also be enabled
by using the undocumented /P2 switch outside the environment. Two pass
assembly catches the error and produces the desired message.

Microsoft has confirmed this to be a problem in QuickC Version 2.01.
We are researching this problem and will post new information here as
it becomes available.

The following source code assembles without errors with one pass
enabled but should generate an error on a short backward jump of
further than 128 bytes.

          .model small

          .code

start:    mov ax, DGROUP
          mov ds, ax
          xor cx, cx

back:     inc cx
          cmp cx, 2
          jmp done

          xor ax,ax       ; You need 60 or so of these pups.
          xor ax,ax
          .
          .
          .
          xor ax,ax
          xor ax,ax

          jmp short back

done:     mov ax, 4c00h
          int 21h

          end start

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