[Bug target/45263] registers used in __do_global_ctors can get clobbered

[mschulze at ivs dot cs.ovgu.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45263

--- Comment #7 from Michael Schulze <mschulze at ivs dot cs.ovgu.de> 2010-11-30 15:16:20 UTC ---
Created attachment 22579
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22579
alternative patch using register r15 instead of r20 avoids pushing/poping

In reaction to bug 29141, which is still pending and not fixed, I offer a patch
that corrects the handling of global constructors. The fix proposed in bug
29141 leads to wrong handling of global constructors since gcc version 4.4.0.
And this is independent of the 64kB boundary because the handling is always
wrong.

With the first provided patch the register r20 was always pushed and popped but
this is not necessary. The global-constructors patch avoids this and uses r15
instead of r20. Due to the compiler abi the register r15 is left unchanged by
called routines, and it has to be saved/restored by routines that use it.

I applied the global-constructor patch and then the compiler generates correct
code for the execution of global constructors regardless of whether the
constructor is located below or above 64kB. I tested the patch by my own but I
think it needs further tests. Please try it out. I think without such a patch
independent of using my one or the r20 patch, this bug is a show stopper since
gcc version 4.4.0.