m68k --register-prefix-optional and labels like registers

[Nick Clifton]

Hi Vincent,

> $ cat foo.s
>         clr.w sp.0

> $ as foo.s -o foo.o --register-prefix-optional
> foo.s: Assembler messages:

> This is a problem because :
> 1) The default value of flag_reg_prefix_optional is 1, except when 
> M68KCOFF or OBJ_ELF are defined (see REGISTER_PREFIX_OPTIONAL in 
> gas/config/tc-m68k.h).
> 2) gcc generates labels like this

How ?  (ie can you provide a gcc based test case.  Please also mention 
how the toolchain is configured).

In fact, please could you open a bug report for this problem so that we 
can track it, and its solution.

> Why is the default value of the option --register-prefix-optional is not 
> the same for all m68k targets ?

This must be historical.  The description of the 
--register-prefix-optional switch in gas/doc/c-m68k.texi mentions that 
register prefixing was needed for the sun3, amongst other targets, so 
presumably the sources evolved from this basis.

 > Do you think gcc should avoid to generate labels like this ?

No.  There is no way that gcc can guarantee not to generate labels like 
this.  A sufficiently determined programmer can always arrange to get 
them into the assembler output somehow.

 > Do you think gas should accept labels like this, even with
 > --register-prefix-optional ?

Yes, but there is always going to be a problem with labels that look 
like register names.  For example if the label in your test had been 
"sp.w" then the assembler would be right to complain.

Cheers
   Nick