2005-03-10 02:25:25

by David Gibson

Subject: [PPC64] Allow emulation of mfpvr on ppc64 kernel

Andrew, please apply.

Allow userspace programs on ppc64 to use the (privileged) mfpvr
instruction to determine the processor type. At the moment it
emulates the instruction to provide the real PVR value, though it
could be made to lie in future if for some reason we wish to restrict
what CPU features userspace uses.

If nothing else this means that some existing ppc32 applications will
now run on a 64-bit kernel (the 32-bit kernel has long supported this
emulation). It will also be necessary for ppc64 perfctr support,
where userspace requires finer-grained cpu type information than the
kernel in order to correctly program the performance monitor control
registers.

Signed-off-by: David Gibson <[email protected]>

Index: working-2.6/arch/ppc64/kernel/traps.c
===================================================================
--- working-2.6.orig/arch/ppc64/kernel/traps.c 2005-03-06 07:08:24.000000000 +1100
+++ working-2.6/arch/ppc64/kernel/traps.c 2005-03-10 13:05:25.000000000 +1100
@@ -279,6 +279,9 @@
* fault. Return zero on success.
*/

+#define INST_MFSPR_PVR 0x7c1f42a6
+#define INST_MFSPR_PVR_MASK 0xfc1fffff
+
#define INST_DCBA 0x7c0005ec
#define INST_DCBA_MASK 0x7c0007fe

@@ -297,6 +300,15 @@
if (get_user(instword, (unsigned int __user *)(regs->nip)))
return -EFAULT;

+ /* Emulate the mfspr rD, PVR. */
+ if ((instword & INST_MFSPR_PVR_MASK) == INST_MFSPR_PVR) {
+ unsigned int rd;
+
+ rd = (instword >> 21) & 0x1f;
+ regs->gpr[rd] = mfspr(SPRN_PVR);
+ return 0;
+ }
+
/* Emulating the dcba insn is just a no-op. */
if ((instword & INST_DCBA_MASK) == INST_DCBA) {
static int warned;
@@ -390,11 +402,6 @@
if (regs->msr & 0x100000) {
/* IEEE FP exception */
parse_fpe(regs);
-
- } else if (regs->msr & 0x40000) {
- /* Privileged instruction */
- _exception(SIGILL, regs, ILL_PRVOPC, regs->nip);
-
} else if (regs->msr & 0x20000) {
/* trap exception */

@@ -411,7 +418,7 @@
_exception(SIGTRAP, regs, TRAP_BRKPT, regs->nip);

} else {
- /* Illegal instruction; try to emulate it. */
+ /* Privileged or illegal instruction; try to emulate it. */
switch (emulate_instruction(regs)) {
case 0:
regs->nip += 4;
@@ -423,7 +430,12 @@
break;

default:
- _exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
+ if (regs->msr & 0x40000)
+ /* priveleged */
+ _exception(SIGILL, regs, ILL_PRVOPC, regs->nip);
+ else
+ /* illegal */
+ _exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
break;
}
}


--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist. NOT _the_ _other_ _way_
| _around_!
http://www.ozlabs.org/people/dgibson

2005-03-10 22:20:54

by Ingo Oeser

Subject: Re: [PPC64] Allow emulation of mfpvr on ppc64 kernel

David Gibson wrote:
> Andrew, please apply.
>
> Allow userspace programs on ppc64 to use the (privileged) mfpvr
> instruction to determine the processor type. At the moment it
> emulates the instruction to provide the real PVR value, though it
> could be made to lie in future if for some reason we wish to restrict
> what CPU features userspace uses.

Why not putting the required information into the AUX table
when executing your ELF programs? I loved this feature in the
ix86 arch.


Regards

Ingo Oeser

2005-03-11 00:40:00

by David Gibson

Subject: Re: [PPC64] Allow emulation of mfpvr on ppc64 kernel

On Thu, Mar 10, 2005 at 11:17:03PM +0100, Ingo Oeser wrote:
> David Gibson wrote:
> > Andrew, please apply.
> >
> > Allow userspace programs on ppc64 to use the (privileged) mfpvr
> > instruction to determine the processor type. At the moment it
> > emulates the instruction to provide the real PVR value, though it
> > could be made to lie in future if for some reason we wish to restrict
> > what CPU features userspace uses.
>
> Why not putting the required information into the AUX table
> when executing your ELF programs? I loved this feature in the
> ix86 arch.

Because this is easy and is the way we already do it on ppc32..?

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist. NOT _the_ _other_ _way_
| _around_!
http://www.ozlabs.org/people/dgibson

2005-03-11 02:34:23

by Paul Mackerras

Subject: Re: [PPC64] Allow emulation of mfpvr on ppc64 kernel

Ingo Oeser writes:

> Why not putting the required information into the AUX table
> when executing your ELF programs? I loved this feature in the
> ix86 arch.

We do put an AT_HWCAP entry in the aux table, which is a bitmap of
features supported by the cpu. But for some applications, such as
programming the performance monitor hardware, you need to know the
specific CPU model and version, and this is a way to provide that
information.

Paul.