Re: ARM/THUMB long calls stubs

[Nick Clifton <nickc at redhat dot com>]

Hi Sami,

> So foo() gets called directly with 'bl' but bar() (in test2.c) gets called
> as "wanted".

Right - this is because foo() is defined in the same file as the 
function that calls it: _start().  GCC makes the (reasonable) assumption 
that since both foo() and _start() are going to be compiled together and 
placed into the same output section that it knows how far apart they are 
and that it can avoid the overhead of the long-call.  In fact at high 
optimisation levels it might even in-line the code from foo() into _start().

The way to avoid this "feature" (I hesitate to call it a bug) is to 
compile your code with the "-ffunction-sections" switch added to the GCC 
command line.  This tells GCC to place each function into its own 
separate section, and GCC is smart enough to know that different 
sections may not end up close to each other, so it cannot optimise away 
the use of the long call.

Cheers
  Nick