From: Scott Wood <scottwood@freescale.com>
To: Bhushan Bharat-R65777 <R65777@freescale.com>
Cc: Wood Scott-B07421 <B07421@freescale.com>,
Michael Neuling <mikey@neuling.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: BOOKE KVM calling load_up_fpu from C?
Date: Wed, 13 Feb 2013 11:37:27 -0600 [thread overview]
Message-ID: <1360777047.6853.3@snotra> (raw)
In-Reply-To: <6A3DF150A5B70D4F9B66A25E3F7C888D065A3511@039-SN2MPN1-023.039d.mgd.msft.net> (from R65777@freescale.com on Tue Feb 12 22:17:00 2013)
On 02/12/2013 10:17:00 PM, Bhushan Bharat-R65777 wrote:
>=20
>=20
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Wednesday, February 13, 2013 6:53 AM
> > To: Bhushan Bharat-R65777
> > Cc: Wood Scott-B07421; Michael Neuling; =20
> linuxppc-dev@lists.ozlabs.org
> > Subject: Re: BOOKE KVM calling load_up_fpu from C?
> >
> > On 02/12/2013 07:18:14 PM, Bhushan Bharat-R65777 wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Wood Scott-B07421
> > > > Sent: Wednesday, February 13, 2013 12:03 AM
> > > > To: Bhushan Bharat-R65777
> > > > Cc: Michael Neuling; Wood Scott-B07421;
> > > linuxppc-dev@lists.ozlabs.org
> > > > Subject: Re: BOOKE KVM calling load_up_fpu from C?
> > > >
> > > > On 64-bit, though, there's a store to the caller's stack frame
> > > > (yuck) which the kvm/booke.h caller is not prepared for.
> > >
> > > So if caller is using r12 then it can lead to come corruption, =20
> right ?
> >
> > No, r12 is a volatile register in the ABI, as is r9. The issue is =20
> that the
> > stack can be corrupted.
>=20
> What do you mean by stack is corrupted?
load_up_fpu() makes assumptions about the caller's stack frame that =20
aren't true when called from C code.
> My understanding is that when calling the assembly function from C =20
> function then stack frame will not be pushed and assembly function =20
> uses the caller stack frame.
Huh? Assembly functions obey the same ABI as C functions (at least, =20
asm functions meant to be callable from C do). If the above were true, =20
how would C code know that it's calling an asm function, and how would =20
it know how much stack to create and which portions would be clobbered?
The issue with load_up_fpu() is that it was apparently not meant to be =20
called directly from C code.
-Scott=
prev parent reply other threads:[~2013-02-13 17:37 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-12 3:29 BOOKE KVM calling load_up_fpu from C? Michael Neuling
2013-02-12 3:37 ` Bhushan Bharat-R65777
2013-02-12 3:46 ` Michael Neuling
2013-02-12 3:58 ` Bhushan Bharat-R65777
2013-02-12 4:16 ` Michael Neuling
2013-02-12 9:01 ` Bhushan Bharat-R65777
2013-02-12 18:33 ` Scott Wood
2013-02-12 22:51 ` Michael Neuling
2013-02-13 1:18 ` Bhushan Bharat-R65777
2013-02-13 1:23 ` Scott Wood
2013-02-13 1:26 ` Bhushan Bharat-R65777
2013-02-13 4:17 ` Bhushan Bharat-R65777
2013-02-13 17:37 ` Scott Wood [this message]
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