On 5/17/22 14:49, Helge Deller wrote: > In 2004 Randolph added the shr() assembly macro and noted that the > source and target register could not be the same. > > I did not find any confindence in the docs for this restriction. Maybe > it's related that on PA2.0 the upper bits may be clobbered? Looking at the generated kernel code from C-files, I'll find all over usages of extru source, x,y, target where source and target are the same register. So, at least for 32-bit this restriction can't be true. Any ideas why this restriction could have been added to the comments? Helge > Anyway, add a compile-time check for it now. > > Signed-off-by: Helge Deller <deller@xxxxxx> > > diff --git a/arch/parisc/include/asm/assembly.h b/arch/parisc/include/asm/assembly.h > index ea0cb318b13d..ca1a12ae5ee7 100644 > --- a/arch/parisc/include/asm/assembly.h > +++ b/arch/parisc/include/asm/assembly.h > @@ -146,6 +146,9 @@ > /* Shift Right - note the r and t can NOT be the same! */ > .macro shr r, sa, t > extru \r, 31-(\sa), 32-(\sa), \t > +.ifc \r,\t > + .error "Can not used the same register (\r) in shr/extru as source and target register." > +.endif > .endm > > /* pa20w version of shift right */
