arm inline assembly 4.8 vs. 4.9 [solved]

[Gene Smith]

On 3/10/2015 6:40 PM, Gene Smith wrote:
> The following inline assembly works as I want with gcc 4.8.3 and
> produces the result shown:
>
> __asm (
>    "ldr r0, =%[addrOfIoPorts]\n"
>    :                                /* no output */
>    : [addrOfIoPorts] "g" (&ioPorts) /* input */
>    : "r0");                         /* clobber */
>
>   801b9e2:    4822          ldr    r0, [pc, #136]
>
> But when compiled with 4.9.3 the linker says "undefined reference to
> `r3'. This is because the produced assembly becomes such that r3 looks
> like a constant:
>
> ldr r0, =r3
>
> I have been unable to find a modification to the original code that
> works with 4.9.3. Any ideas or suggestions?
>

A helpful reply via emailed suggested the use of other constraints:

"Using "g" allows "Any register, memory or immediate integer operand." 
Such being the case, have you tried replacing it with each of "m", "r" 
and "i"?  I would expect "m" to work for you."

I replied:

I think I had tried all of these. But tried again.
"m" causes "error: memory input 0 is not directly addressable"

"r" is same as "g": undefined reference to `r3'

"i" worked! Obviously I didn't try this.  I should have looked closer in 
the latest gcc manual under "constraints" -- "i": An immediate integer 
operand (one with constant value) is allowed. This includes
symbolic constants whose values will be known only at assembly time or
later. (So maybe it was a bug that 4.8.3 worked with "g" in this context?)

No build errors and now see these again in obj dump under 4.9.3:
  801b4c8:    486c          ldr    r0, [pc, #432]    ; (801b67c ...

Thanks!