Altivec Vector code bug

Altivec Vector code bug

[John Whitney]

[-- Attachment #1: Type: text/plain, Size: 674 bytes --]

The attached patch corrects the following problem with the Altivec
vector:

When running Linux 2.6.5-rc2 (Altivec NOT configured in) on a 7410-base
platform, and running a program that attempts to use a vector register,
the kernel will lock up.  This is due to vectoring to 0xf20, which is
in the middle of the exception prolog as the exception handler is now
written.

To correct this, I reverted to the method used by the 2.4.25 kernel
(arch/ppc/kernel/head.S):

	. = 0xf00
	b Trap_0f

	. = 0xf20
#ifdef CONFIG_ALTIVEC
	b AltiVecUnavailable
#endif
Trap_0f:
	<exception handling code>

This causes the kernel to not lock up, regardless of the altivec
configuration.

John


[-- Attachment #2: altivec.patch --]
[-- Type: application/octet-stream, Size: 466 bytes --]

--- linuxppc-2.6.5-rc2.orig/arch/ppc/kernel/head.S	2004-04-01 14:21:53.000000000 -0500
+++ linuxppc-2.6.5-rc2/arch/ppc/kernel/head.S	2004-04-06 16:12:12.000000000 -0400
@@ -493,13 +493,14 @@
  * We effectively remap it to 0x3000.
  */
 	. = 0xf00
-
-#ifdef CONFIG_ALTIVEC
 	b	Trap_0f
+
 	. = 0xf20
+#ifdef CONFIG_ALTIVEC
 	b	AltiVecUnavailable
-Trap_0f:
 #endif
+
+Trap_0f:
 	EXCEPTION_PROLOG
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	EXC_XFER_EE(0xf00, UnknownException)

Re: Altivec Vector code bug

[Benjamin Herrenschmidt]

On Wed, 2004-04-07 at 06:19, John Whitney wrote:
> The attached patch corrects the following problem with the Altivec
> vector:
>
> When running Linux 2.6.5-rc2 (Altivec NOT configured in) on a 7410-base
> platform, and running a program that attempts to use a vector register,
> the kernel will lock up.  This is due to vectoring to 0xf20, which is
> in the middle of the exception prolog as the exception handler is now
> written.

Thanks, forwarded upstream.

Ben.


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