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Powerpc IRQ handling breaks strict EABI compliance



Joel Sherrill <joel.sherrill at oarcorp.com> writes:
> Sergei Organov wrote:
> > 
> > Till Straumann <strauman at SLAC.Stanford.EDU> writes:
> > > OK, I fixed the motorola/shared BSP to not clobber R2/R13 anymore.
> > > However, the question remains:
> > >
> > >   - who is responsible for the setup (calling __eabi()) ?
> > >     RTEMS or application code?
> > 
> > It's main() that when compiled with corresponding gcc switches automatically
> > invokes __eabi(). It basically only setups R2/R13. BTW, R13 is being used even
> > without EABI -- R13 usage is part of SYSV ABI which EABI is derived from.
> > 
> > This brings another interesting problem. In older days of RTEMS the 'main' was
> > part of RTEMS, not the part of application code, so it was invoked very early
> > and thus all RTEMS/BSP initialization went after __eabi() has been called.
> > AFAIK, now situation is different and __eabi() will be invoked too late. It
> > means that RTEMS startup code should invoke __eabi() (or setup R13/R2 itself)
> > for things to work correctly as C startup/initialization code compiled for
> > SYSV ABI/EABI will already rely on correct values in R2/R13.
> 
> RTEMS now ensures that the first thread to execute invokes the appropriate
> routine for that gcc target to run global constructors. The powerpc-rtems
> gcc target is noted as being an init/fini target so it will call _init().
> 
> > What I want to tell is that using of SYSV ABI/EABI indeed makes code smaller
> > and faster, so it'd be fine if PPC port of RTEMS starts to support it again
> > (the old RTEMS 3.x code did support it, BTW).
> 
> The application owning main() was generally viewed as an improvement. :)

And I believe it is.

> 
> In the olden days, main() happened too early and drivers were not yet
> initialized. This lead to situations where global constructors could not
> print or do other operations.

That's why I called routine that invokes global constructors from the
postdriver_hook ;-)

I myself overwrite __eabi() with an empty routine and do its work myself early
in the startup code (along with copying of data from ROM to RAM / zeroing
required sections / setup initial C stack, etc.). In fact setting of R13/R2
isn't a big deal compared to the rest of asm initialization.

-- 
Sergei.