Re: Using memory below the SP (Was: Q: P6 branch prediction)

Michael Meissner <meissner@cygnus.com>
24 May 1996 15:34:40 -0400

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Related articles
Re: Q: P6 branch prediction conway@rimmer.cs.mu.OZ.AU (1996-05-01)
Re: Q: P6 branch prediction khays@sequent.com (1996-05-14)
Re: Using memory below the SP (Was: Q: P6 branch prediction) zalman@macromedia.com (1996-05-18)
Re: Using memory below the SP (Was: Q: P6 branch prediction) meissner@cygnus.com (Michael Meissner) (1996-05-24)
| List of all articles for this month |
From: Michael Meissner <meissner@cygnus.com>
Newsgroups: comp.compilers
Date: 24 May 1996 15:34:40 -0400
Organization: Compilers Central
References: <3179B05D.2781@cs.princeton.edu> <4m6ufs$msc@mulga.cs.mu.OZ.AU> 96-05-012 96-05-100 96-05-105
Keywords: architecture

zalman@macromedia.com (Zalman Stern) writes:


| Using the IBM calling convention on PowerPC, the 64 bytes immediately
| below the stack pointer (that is just outside the stack region) are
| guaranteed to be useable by a fucntion. This gives a function access
| to a small amount of memory without the expense of buying a stack
| frame. So on that platform, this technique is undeniably safe.


Its actually 220 bytes according to the ABI (so that r31 - r13, and f31 - f14
can be stored before updating the stack pointer). This usage is in fact
blest by the ABI (page 3-26 of the June 30th PowerOpen ABI).


Note, for the System V.4 and EABI ABI's, there is no such guarantee of space
beyond the current stack pointer.


--
Michael Meissner, Cygnus Support (East Coast)
Suite 105, 48 Grove Street, Somerville, MA 02144, USA
meissner@cygnus.com, 617-629-3016 (office), 617-629-3010 (fax)


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