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Re: [Qemu-devel] [PATCH] ignore reads to the EOI register.

From: Glauber Costa
Subject: Re: [Qemu-devel] [PATCH] ignore reads to the EOI register.
Date: Fri, 28 Mar 2008 09:59:32 -0300
User-agent: Thunderbird (X11/20071115)

Aurelien Jarno wrote:
On Wed, Mar 26, 2008 at 09:57:16PM -0300, Glauber Costa wrote:
They seem legal in real hardware, even though the EOI
is a write-only register. By "legal" I mean they are completely
ignored, but at least, don't cause any bits to be set at ESR.

Without this patch, some (very recent) linux git trees will fail
to boot in i386.

This is generated from kvm-userspace, but should apply well to
plain qemu too.

Signed-off-by: Glauber Costa <address@hidden>
 qemu/hw/apic.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/qemu/hw/apic.c b/qemu/hw/apic.c
index 92248dd..4102493 100644
--- a/qemu/hw/apic.c
+++ b/qemu/hw/apic.c
@@ -615,6 +615,8 @@ static uint32_t apic_mem_readl(void *opaque, 
target_phys_addr_t addr)
         /* ppr */
         val = apic_get_ppr(s);
+    case 0x0b:
+        break;

While I agree the guest should not care of the value (it should actually
not read it), wouldn't it be safer to return a default value (0 ?) instead of an initialized value?

I don't think it would really make any difference, but is not opposed to this solution either.

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