Bug in FASM v1.69.37

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CandyMan

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

CandyMan 14 Feb 2012, 01:24

format MS64 COFF

section '.text' executable

virtual at 0
SortReverse db ?
end virtual

ReturnRDX:
lea rdx,[SortReverse] ;error: invalid use of symbol
ret

14 Feb 2012, 01:24

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8394
Location: Kraków, Poland

Tomasz Grysztar 14 Feb 2012, 01:37

It is actually due to a bugfix - previous fasm versions incorrectly allowed "lea rdx,[0]" (this is what it is, the "virtual" thing is not an important detail here) to be assembled in such context, and it generated incorrect opcode. Because in 64-bit mode address that has no size prefix is declared to be always RIP-relative, and it is not possible to generate relocation to address absolute "0" relative to RIP. It is like writing "lea rdx,[rip-$+0]", which in turn fails for the same reason as "dd 0-$" does.
To generate a correct instruction which will load absolute value into RDX, you need to use construction like:

Code:

lea rdx,[dword SortReverse]

14 Feb 2012, 01:37

SFeLi

Joined: 03 Nov 2004
Posts: 138

SFeLi 18 Feb 2012, 22:27

Is something wrong with this code or with the fasm itself?

Code:

repeat 2
  virtual at 0
    db 'aa'
    db 'zz'
    ; UNCOMMENT_ME = 1
    load foo from %-1
    load bar from %-1+2
  end virtual
  baz = foo + bar
end repeat

18 Feb 2012, 22:27

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8394
Location: Kraków, Poland

Tomasz Grysztar 18 Feb 2012, 23:23

Yes, this is a correct code and should be working. I'm uploading the correction as 1.69.38.

18 Feb 2012, 23:23

SFeLi

Joined: 03 Nov 2004
Posts: 138

SFeLi 18 Feb 2012, 23:56

So fast! Thank you)

18 Feb 2012, 23:56

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