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From: net@tub.UUCP (Oliver Laumann)
Newsgroups: comp.sys.hp
Subject: alloca() on the HP9000/300
Message-ID: <1455@tub.UUCP>
Date: 8 Aug 90 17:54:48 GMT
Reply-To: net@tub.UUCP (Oliver Laumann)
Organization: Technical University of Berlin, Germany
Lines: 28

I need an implementation of alloca() for the HP9000/3xx.  The alloca()
from libPW.a (which makes use of malloca/free) doesn't work for my 
application; I need an alloca() that actually allocates space on the
stack.  I came up with the following (I snarfed it from the Sun-3's
libc.a and converted the syntax):

_alloca:
    mov.l	(%sp),%a0
    mov.l	4(%sp),%d0
    addq.w	&3,%d0
    and.l	&-4,%d0
    sub.l	%d0,%a7
    mov.l	%sp,%d0
    addq.w	&8,%d0
    jmp		(%a0)

Unfortunately it doesn't work on the HP9000/3xx.  Sometime after my
application has invoked alloca() the first time, the contents of a
register (a local variable) is garbled.

Is it possible to write a "real" alloca() for the HP at all, or is
there some sort of conflict with the C compiler (i.e. does the way
the stack pointer is handled make usage of alloca() impossible)?

Thanks,
--
    Oliver Laumann, Technical University of Berlin, Germany.
    pyramid!tub!net   net@TUB.BITNET   net@tub.cs.tu-berlin.de