Another Vasm question

[LeCaravage]

Hi,

How do you make this without making Vasm shout "error 39 : illegal relocation" ?

add.l #label1-label0,a1


Thanks,

[LeCaravage]

Ok, got it. The pb seems to be found in section. If label1 & label0 are not in the same section than the instruction, vasm don't recognize the labels. Why ? I don't know, because it's a relative value.

[DMWCashy]

This is do to linker relocation, Vasm is unable to calculate the offset between the 2 labels as that is done at link time.

[LeCaravage]

Originally Posted by DMWCashy

This is do to linker relocation, Vasm is unable to calculate the offset between the 2 labels as that is done at link time.

Why not ? Both labels are in the same section. Could it be possible to change this error to a warning with a param sent to vasm ?

[DMWCashy]

I think this is an issue with Vasm, are both labels in the same file?

I may be wrong, but I am sure this has been discussed before on this forum somewhere.

[jotd]

workaround: define a

diff:
   dc.l  label1-label0

in the section where the labels are. Then use this

 add.l  diff,a1

or first add then sub the other value (or precompute it in a register if time critical)

[LeCaravage]

Originally Posted by DMWCashy

I think this is an issue with Vasm, are both labels in the same file?

I may be wrong, but I am sure this has been discussed before on this forum somewhere.

Indeed, I'm no specialist with Vasm but really too bad to make restriction with this feature.
Yes they are in same include file and same section too.

Originally Posted by jotd

workaround: define a

diff:
   dc.l  label1-label0

in the section where the labels are. Then use this

 add.l  diff,a1

or first add then sub the other value (or precompute it in a register if time critical)

Thanks for the tip. (too bad to waste 4 bytes though).

[phx]

Originally Posted by LeCaravage

If label1 & label0 are not in the same section than the instruction, vasm don't recognize the labels. Why ? I don't know, because it's a relative value.

The issue is certainly elsewhere. The difference between two labels in the same section is never a problem, as it is constant. And the two labels also don't have to be in the same section as the instruction - why should they? Example:

frank@nerthus cat tst.s
        code
        add.l   #label1-label0,a1

        data
label0:
        dc.b    1,2,3
label1:
frank@nerthus vasmm68k_mot tst.s
vasm 1.8i (c) in 2002-2020 Volker Barthelmann
vasm M68k/CPU32/ColdFire cpu backend 2.3m (c) 2002-2020 Frank Wille
vasm motorola syntax module 3.14a (c) 2002-2020 Frank Wille
vasm test output module 1.0 (c) 2002 Volker Barthelmann

CODE(acrx2):               2 bytes
DATA(adrw1):               3 bytes

Unlike many other assemblers vasm even supports label differences when the first label is unknown or in a different section, provided that the second label is in the same section as the instruction. Example:

frank@nerthus cat tst.s
        xref    label1
        code
label0:
        add.l   #label1-label0,a1

        data
label1:
frank@nerthus vasmm68k_mot -quiet tst.s
frank@nerthus more a.out
Sections:
section CODE (attr=<acrx> align=2):
(...)
       0: symbol: label0 LAB (0x0) sec=CODE
       0: data(6): d3 fc 00 00 00 02 rpc(2,0-31,0xffffffff,0x2,label1 LAB (0x0) EXPORT REF sec=DATA )

It does this trick by using a 32-bit PC-relative relocation and adapting the addend accordingly. These relocations even work under AmigaOS since OS2.0 (or 3.0?) using HUNK_RELRELOC32.

Originally Posted by LeCaravage

Indeed, I'm no specialist with Vasm but really too bad to make restriction with this feature.
Yes they are in same include file and same section too.

There is no such restriction. Please check your code again or provide an example which reproduces the error. Probably one or both of your labels is undefined or both are in different sections.