TMS570LC4357: serious omission in assembler .cdecls enum handling

Henry Spencer

Part Number: TMS570LC4357

(This is under CCS 7.4.0.00015 -- yes I know it's rather old, I'm dealing with some old code...) In the assembler, simplifying the original greatly:

.cdecls C
%{
enum { CPU_MODE = 0x1f };
%}
.text
and r5, r0, #CPU_MODE

draws an "unknown symbol" error. There doesn't seem to be any way for assembler code to reference a C enumerated constant declared without an enum tag name (which is legal C, and always has been, and is now a fairly common way of declaring integer constants).

over 2 years ago

0 jagadish gundavarapu over 2 years ago

TI__Guru 69811 points

Hi Henry,

Unfortunately, the .cdecls directive is not supported.

Please refer below thread for more details:

(+) TMS570LS1114: tiarmclang: The .cdecls directive is not supported for this target - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

Thanks & regards,
Jagadish.

0 Henry Spencer over 2 years ago in reply to jagadish gundavarapu

Prodigy 60 points

Note the part about "CCS 7.4.0.00015" -- as of that release, .cdecls is there and works, except for this one troublesome case.

0 jagadish gundavarapu over 2 years ago in reply to Henry Spencer

TI__Guru 69811 points

Hi Henry,

Can you please try to declare in below way, and see?

This is working at my side.

Thanks & regards,
Jagadish.

0 Henry Spencer over 2 years ago in reply to jagadish gundavarapu

Prodigy 60 points

I already know that it does work. As I said, the problem is not that .cdecls in general doesn't work (in CCS 7.4.0 and similarly old releases), but that it apparently fails to handle this one particular case: enumerated (not #defined) constants declared without an enum tag name. This matters because the big advantage of .cdecls is being able to use _existing_ C header files, without having to rewrite them for the benefit of the assembler. And some header files declare a lot of constants using the troublesome syntax -- which is legitimate C -- and I'd rather not have to rewrite them all using #define.

What I wondered, mostly, was whether this actually _does_ work except that you have to use some undocumented special syntax to access such names in assembler. Normal assembler access to .cdecls enumerated constants requires writing enumtagname.constantname, so it would make sense that constants declared with no tag name could be reached by using some special placeholder tag name. In fact, this makes rather more sense than the alternative, that the implementers simply didn't implement this case. Unfortunately, the Assembly Language Tools manual doesn't mention the no-tag-name case at all, so there's no hint of what the placeholder would be, and a few experiments with obvious choices were all unsuccessful.

0 jagadish gundavarapu over 2 years ago in reply to Henry Spencer

TI__Guru 69811 points

Henry,

Understood your query.

But i don't have any knowledge on declaration of enum using .cdecls, so i will try to discuss with my internal team once and get back to you on this.

Thanks & regards,
Jagadish.