Low limit for memory mapping

Hi all,

I tried to mmap with the MAP_FIXED flags set to some addresses
starting at 0x1000 and mmap always return EPERM.

However when I can read from this document
(http://www.arm.linux.org.uk/developer/memory.txt):

00001000        TASK_SIZE-1     User space mappings
                               Per-thread mappings are placed here via
                               the mmap() system call.

But I can only map memory above 0x9000 just after where the _text is
mapped. Could someone point me out why I can't use the addresses
between 0X1000 and 0x8000 ?

I can't find any answer neither from the linux kernel source (but I'm
sure it's in it ;) ) nor from this mailing list.

Thanks

Fred.