why does the macro "ZERO_PAGE" take an argument?

["Robert P. J. Day" <rpjday@mindspring.com>]

  probably making a fool of myself here, but what is the purpose of
that single argument to the macro "ZERO_PAGE"?

$ grep -r "define ZERO_PAGE" include
include/asm-frv/pgtable.h:#define ZERO_PAGE(vaddr)      ({ BUG(); NULL; })
include/asm-frv/pgtable.h:#define ZERO_PAGE(vaddr)      virt_to_page(empty_zero_page)
include/asm-v850/pgtable.h:#define ZERO_PAGE(vaddr)     ((void *)0x87654321)
include/asm-mips/pgtable.h:#define ZERO_PAGE(vaddr) \
include/asm-blackfin/pgtable.h:#define ZERO_PAGE(vaddr) (virt_to_page(0))
include/asm-parisc/pgtable.h:#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
include/asm-alpha/pgtable.h:#define ZERO_PAGE(vaddr)    (virt_to_page(ZERO_PGE))
...

  AFAICT, there are no definitions of that macro that actually use
that argument.  is that some kind of historical cruft?

rday
-- 
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA

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