[parisc-linux] Re: [glibc] tststatic failues, reduced to simple testcase.

[Carlos O'Donell]

On Fri, Aug 29, 2003 at 06:44:03PM -0400, John David Anglin wrote:
> > > __asm(
> > > 0x4000883c:     be,l 100(sr2,r0),%sr0,%r31
> > > 0x40008840:     ldi 2,r20                    !! FORK !!
> > > );
> > > 0x40008844:     ldi -1000,r20 <--Corrupted--- r19 = 0x10106368
> 
> Looking at the kernel syscall code, it seems at first glance that
> r19 is saved and restored.  Thus, the problem may be specific to fork.

The first place I went to was syscall.S and entry.S to see if r19 was
saved and restored. It is infact saved and restored, _but_ there seems
to be a case in the sys_fork_wrapper where r19 is written back as a temp
slot (PT_XX struct).

linux-2.4/arch/parisc/kernel/entry.S

   2004         /* These are call-clobbered registers and therefore
   2005            also syscall-clobbered (we hope). */
   2006         STREG   %r2,PT_GR19(%r1)        /* save for child */
   2007         STREG   %r30,PT_GR21(%r1)

This is done just before the call to 'sys_clone', but it's never used
anywhere. The comment indicates that the author believed he had all
right to use caller saves registers, and they should.

Aflicted: sys_fork_wrapper, sys_clone_wrapper, sys_vfork_wrapper

I'm tempted to remove the store and load of call-clobbered registers
from our syscall path, push them into the glibc wrappers, and see what 
happens :)

c.