> On Fri, 20 Jul 2001, Ben Harris wrote:
> 
> : > What else is required?
> :
> : MASK_RETURN_ADDR needs to be changed to generate code to check what mode
> : the CPU is in at run-time and pick the correct mask appropriately.
> : sys/arch/arm/include/profile.h demonstrates how to do this, but it needs
> : to be converted to a form GCC can understand.
> 
> The mask is needed when gcc is *compiling* code, so how would this be done
> at run-time?  (Generation of code that does it on every return insn?  Eek,
> that sounds like a significant overhead added to function calls....)  Note
> I'm reading from your definition of "run-time" here that you are implying
> a program's run-time, not gcc's.
> 

No, the only time it's needed is when we need to examine the return 
address in "C" code.  At run time the architecture just gets extracting 
the return bits right.  C code unpicking the stack however, has to throw 
away the bits that don't count.  In practise this will only occur when 
unwinding an exception.

R.