As with perl 5.8, the presence (or absence) of the backslash seems to make no difference at all.

(Note that, in any case, it won't have any effect on the actual warnings I quoted - as they occur during the compilation of the C code, long before any arguments actually get passed to foo.)

I was curious to see what happened on linux with 5.6, but make didn't like the makefile that Configure created and I quickly lost interest in building perl 5.6 on my linux box.

I'll assume the warnings are benign ... until evidence to the contrary presents itself.

Cheers,
Rob