32bit ARM assembler.

I am trying to assemble some old code and get a warning

ARM AOF Macro Assembler 4.01 (Acorn Computers Ltd) [04 Jul 2011]
Warning: Deprecated instruction (STM with SP or PC in register list)Unable to start throwback session, error 0×20603 ‘No task registered for throwback’

Assembled program starts

AREA |C$$code|, CODE, READONLY
IMPORT |x$stack_overflow|
EXPORT |revsprite|
startx
DCB “revsprite”,0
ALIGN
starty
DCD &ff000000 + starty – startx

revsprite
MOV ip, sp
STMFD sp!,{r0,r1,r2,r3,r4,r5,r6,r7,r8,r9,fp,ip,lr,pc } ; save two parms and work regs
SUB fp, ip, #4
CMPS sp, sl
BLLT |x$stack_overflow|

and ends

;***************************************************
; return *
;***************************************************
LDMEA fp,{r4,r5,r6,r7,r8,r9,fp,sp,pc}^ ; restore work regs leave args on stack for
; backtrack
END

What is the correct coding these days?

Well, you should never normally be pushing PC.

Next, you’ve got a stack imbalance because you’ve pushed one more register than you’ve pulled, even accounting for the odd “leaving R0-R3 behind” thing.

On top of that, you shouldn’t be doing LDM^ – this isn’t 32 bit safe; you don’t need the ^.

Finally, why doesn’t the LDM also use FD? That would be much clearer.

Oh, if this was code in a RISC OS build environment, you could GET Hdr:Macros and use Push/Pull or even better Entry/EXIT macros.

Apart from that, the STM/LDMs are fine. ;)

The “No task registered for throwback” message means the system hasn’t seen an editor that can handle throwback (listing warnings and errors in a special window) – editors such as Zap or StrongEd certainly do. Not sure about Edit or SrcEdit (can’t say I’ve ever really used either).

Steady on there Steve! That’s an APCS function entry/exit veneer that you’re looking at, so everything you’re seeing is perfectly normal. (I’ll just assume you’re suffering from sleep deprivation, shall I? ;-)) The only bit that’s “wrong” is the LDM ^, since as you’ve pointed out that isn’t 32bit safe.

I’m tempted to say that you should just ignore the deprecated instruction warning. You could get round it by splitting the STM into a STM and STR, but since the current version of Norcroft generates code which falls foul of the same warning, and the PC value that gets pushed will only be used for debugging, it’s not a particularly serious issue.

AREA |C$$code|,CODE,READONLY
IMPORT |x$stack_overflow|
EXPORT |revsprite|
|startx|
DCB “revsprite”,0
ALIGN
|starty|
DCD &ff000000 + |starty| – |startx|

;***************************************
; return *
;****************************************
LDMDB fp,{r4-r9,fp,sp,pc}

; remove ^ from pc}^
; cmps the s not required
; you can group together the regs ie r0-r9
; you can use stmdb/ldmdb

; restore work regs leave args on stack for
; backtrack
END

The above assembles – the GCC and Acorn Compilers use it.
The other error – what text editor do you use?

That’s an APCS function entry/exit veneer that you’re looking at, so everything you’re seeing is perfectly normal

Really? It looks bonkers to me… I really must be tired. :(

Colin, did you really mean STMDB/LDMDB? That seems a bit suspect to me. But as we’ve already established, I’m not firing on all cylinders… :)

Well I think I probably got the coding from the Norcroft C manual which I am guessing had a section on calling assembler from C. This is back in the 26bit days and I no longer have the manual. Would be nice to see some documentation on how one is supposed to Call assembler from C these days for 32 bit with some clarification on making 26bit tolerant.
Anybody able to point to such documentation, I have not yet found anything in the ROOL development kit.