On Sat, 21 Aug 1999, Philip Blundell wrote:
> > Why can the linker not deal with function calls more then a 26 bit
> >address offset from teh PC?
>
> The B instruction only has a 24-bit displacement field. That stores a number
> of words which gives you a 26-bit address offset. To do jumps beyond that,
> the linker would have to bounce the call through a PLT entry. It probably
> wouldn't be too hard to make this happen automatically for out of range
> jumps if you wanted (though this should be controlled by a switch). As a
> matter of passing interest modutils already does something a bit like this
> so that kernel modules can be quite distant from the main code body.
>
> Another possibility would be to extend the compiler and/or assembler to let
> you declare a particular function call as being "long" and have that generate
> code that rather than a straightforward branch contained code a bit like this:
>
> mov lr, pc
> ldr pc, =target
A C construct like this should also do the trick:
extern void func();
void (*target)() = func;
foo()
{
target();
}
Nicolas Pitre, B. ing.
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