From: David Edelsohn <dje@watson.ibm.com>
To: Kumar Gala <kumar.gala@freescale.com>
Cc: linuxppc-dev list <linuxppc-dev@ozlabs.org>, linuxppc64-dev@ozlabs.org
Subject: Re: CONFIG_FRAME_POINTER on ppc/ppc64?
Date: Tue, 16 Aug 2005 00:03:16 -0400 [thread overview]
Message-ID: <200508160403.j7G43Hd29692@makai.watson.ibm.com> (raw)
In-Reply-To: Message from Kumar Gala <kumar.gala@freescale.com> of "Mon, 15 Aug 2005 22:41:03 CDT." <473FD762-FB04-4B63-93E9-11931492AC60@freescale.com>
>>>>> Kumar Gala writes:
>> Because -fomit-frame-pointer and -fno-omit-frame-pointer have no
>> effect on ppc or ppc64, I assume. :)
Kumar> I'm assuming that's a guess. The reason I ask that is my memory
Kumar> serves correctly r31 is used as the frame pointer if compiled that
Kumar> way. Maybe some GCC expert can chime in. I'll copy David Edelsohn
Kumar> and see if I get a response :)
I am missing some context here. On both 32-bit PowerPC Linux
(PowerPC SVR4) and 64-bit PowerPC Linux, GPR r31 is used as the frame
pointer. PowerPC does not have a dedicated frame pointer and the PowerPC
ABI does not require an independent frame pointer in a function at all
times, so it can be omitted by default. If the frame pointer is not
referenced for any unique needs, uses of the frame pointer are adjusted to
reference the stack pointer. GCC only retains the PowerPC frame pointer
when dynamic stack allocation (alloca) is used within a function.
-fomit-frame-pointer has no effect on PowerPC because it is enabled by
default.
David
next prev parent reply other threads:[~2005-08-16 4:03 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-08-15 18:25 CONFIG_FRAME_POINTER on ppc/ppc64? Kumar Gala
2005-08-15 23:08 ` Paul Mackerras
2005-08-16 3:41 ` Kumar Gala
2005-08-16 4:03 ` David Edelsohn [this message]
2005-08-16 5:23 ` Paul Mackerras
2005-08-16 9:44 ` Segher Boessenkool
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