DCD & AOF relocation

I have assembler of the form

AREA A,CODE,READONLY
 IMPORT f
g
        DCD g - f
 END

which objasm (4.08) does not accept. The intention is that f will be the start of the target image. In the file where f is defined this works, as described in the objasm manual section on modules.

Is there a way to write the offset from the image start like this? Alternatively, is there way to just write

     DCD g

and stop __RelocCode getting its mitts on the DCD?

The plot thickens…

To use SharedCLibrary I link with C:o.stubs, but Link will only put the necessary relocations in the RelocCode table if I do

Link -rmf

rather than

Link -rmf -B &0

The latter results in ‘Unknown library chunk’, presumably due to RelocCode not fixing up the stubs. However the former defaults to linking with base &8000, which causes the difficulty from my original post (cannot form DCD <offset from module start> unless in same source file as module start).

Is there a way to force Link to put in the relocations for the SCL stubs, while having base address 0?

unless in same source file as module start).

I’m a little confused as to what you’re trying to do. Modules are relocatable by definition, so the base address should be, as you note, a calculation from the start.

But, then, the header with all the offsets should be the very first thing in the module. Literally you define a label that represents the module start, and the header with all the X – Y stuff directly follows.
So I don’t understand why this base address is in a different file.

Next, the use of CLib. In an assembler module? You need to set up the C environment (basically doing what CMHG does). It’s probably a lot simpler to discard the assembler and write the module in C if you want CLib functions….?

I’ve settled for doing this:

AREA ZZZZRelocCorrect,READONLY,CODE

 EXPORT	RelocCorrect

 IMPORT |C$$code$$Base|
 IMPORT |__RelocCode|
 IMPORT	|Image$$RO$$Base|

base_address	&	|Image$$RO$$Base|
end_offset		*	&B0
c_code_address		&	|C$$code$$Base|

; Must be run after RelocCode so that all the symbols have
; the correct values
RelocCorrect	ROUT
	ADR	R0,|__RelocCode|
	ADD	R0,R0,#end_offset
	LDR	R1,base_address
	LDR	R2,c_code_address
	SUB	R2,R2,R1	; R2 = offset of C$$Code from mod start
01	LDR	R3,[R0],#4	; Get offset for next word to do
	CMP	R3,#-1	; End of list?
	MOVEQ	PC,R14
	CMP	R3,R2	; Before C$$Code?
	BHS	%BT01	; No, do next entry
	LDR	R4,[R1,R3]
	SUB	R4,R4,R1   ; Turn absolute back into offset from mod start
	STR	R4,[R1,R3]
	B	%BT01

It works nicely actually, you have to make sure that all the assembler code comes before C$$Code for it to work. Also make sure you do _clib_initialisemodule and RelocCorrect in the right order and strictly before any other assembler gets control.

So long as you don’t want it to go in the ROM…