From: Mikulas Patocka <mpatocka@redhat.com>
Date: Wed, 2 Jul 2008 00:39:35 -0400 (EDT)
The ABI is very vague about it. The V9 ABI just displays that 6-word space
in a figure bug doesn't say anything about it's usage. The V8 ABI just
says that "the function may write incoming arguments there". If it may
write anything other, it is unknown --- probably yes, but it is not said
in the document.
The document nicely specifies who owns which registers, but doesn't say
that about the stack space :-(
Actually, I know for a fact that you have to have those slots there.
A long time ago in the sparc64 kernel, in the trap entry code, I tried
only giving 128 bytes of stack frame as the trap entry called into C
code. And it did not work, I had to put the 6 slots there.