Re: ARM thumb interworking hole?

[Richard Earnshaw <rearnsha at gcc dot gnu dot org>]

On Mon, 2005-01-10 at 04:31, Charles Manning wrote:
> I've read up what I can on this, and seen the "it's a binutils problem" style 
> responses too, but I see something still that seems to me a hole in the 
> current interworking strategy.
> 
> I'm compiling thumb with -mthumb  -mthumb-interwork -mlong-calls
> 
> I'm using -mlong-calls because the code is split between two memory areas 
> which are more than 4MB apart.
> 
> If I have code that calls a function per function pointer then code is 
> generated to use a _call_via_rX stub to call the function pointer.  The 
> problem though is that the call to call_via_rx is not a long call, so when ld 
> tried to do the location it can't  span the jump with the limited  
> capabilities (4MB) of a Thumb branch and we end up with a "relocation 
> truncated to fit" problem.
> 
> It seems to me that this isn't an ld problem since ld can't change a branch 
> into a long branch (??can it??).
> 

Not directly, but it can make it branch to a reachable trampoline that
can then do the long branch.  Indeed, this is what should be done in
general rather than using -mlong-calls, since it just works everywhere
and has no cost when it's not needed.

R.