RE: [avr-gcc-list] Puzzling behaviour of rjmp in assembler

[Tom Harris]

On 6 Dec 2002 at 8:48, Tom Harris wrote:

> Greetings,
> 
> Using avr-gcc 20021111, I assembled the following:
> 
>  .section .text
>  .func i2c_delay_T2
> i2c_delay_T2:        
>  rjmp +2
>  rjmp +2
>  rjmp +2
>  rjmp +2
>  ret          
>  .endfunc     
> 
> using options `-c -x assembler-with-cpp -mmcu=at90s2313`.
> 
> On dumping the output with avr-objdump , the generated code has
> incorrect offsets. `rjmp -2' looks like an infinite loop. This code
> used to work with an old release of avr-gcc, I could find the verion
> if required.
> 
> 00000000 <i2c_delay_T2>:
>    0:   00 c0           rjmp    .+0             ; 0x2
>    2:   ff cf           rjmp    .-2             ; 0x2
>    4:   fe cf           rjmp    .-4             ; 0x2
>    6:   fd cf           rjmp    .-6             ; 0x2
>    8:   08 95           ret
> 
> Is this a bug or what?
> 

Unfortunately the old version of avr-gcc that assembled 'rjmp +2' as if it
were 'rjmp .+2' has gone from our server to the great bit bucket in the sky,
so its version is unknown, but I think that it was released in 2001. I can
confirm that it used to behave this way, as I have code in source control
that I had to modify to work with version 20021209. It's probably only of
academic interest now that an old version of avr-gcc was broken. 

Thanks for the interest.

TomH <tomh(AT)optiscan(DOT)com>
avr-gcc-list at http://avr1.org