RE: [Xen-ia64-devel] stack corruption creating idle domain

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Alex Williamson
>Sent: 2006年1月25日 3:16
>
>   I've been debugging a hang that I see on current xen-unstable.hg and
>I'm looking for suggestions.  The hang occurs just after xen prints
>"About to call scheduler_init()".  I've traced the problem with ski and
>it appears that in init_switch_stack we blow away the stack with the
>memset of the switch_stack and pt_regs area.  The problem seems to be
>that we're setting idle_vcpu[0] to the address in r13 (back in
>start_kernel), but we haven't set r13 to anything that necessarily has
>enough space for idle_vcpu[0].  Am I missing the setup of r13?  The

Hi, Alex,
        I don't quite catch you in above sentence. What's the problematic value 
for r13 in your case? Ideally r13 is initialized to init_task in very early 
setup in head.S. Then later it's referred further as idle_vcpu[0]. It's 
harmless to clear switch stack and pt_regs area for idle vcpu0 at that point. 
So you may need to figure out where r13 is getting changed before that point.

Thanks,
Kevin

>trivial patch below works around the problem, but perhaps I'm
>overlooking some intricacy about how this is supposed to work.
>
>   BTW, I only see this problem when using gcc-3.3.5.  That compiler
>decides to use the stack in init_switch_stack causing us to infinitely
>page fault when we get back from the memset.  I have observed in ski
>that a xen image compiled with gcc-4.0 also overwrites the stack, but
>nothing critical seems to be using it.  What's the correct fix here?
>Thanks,
>
>       Alex
>
>--
>Alex Williamson                             HP Linux & Open Source Lab
>
>--- a/xen/arch/ia64/xen/xensetup.c      Mon Jan 23 15:27:00 2006
>+++ b/xen/arch/ia64/xen/xensetup.c      Tue Jan 24 05:59:04 2006
>@@ -148,6 +148,8 @@
>     .stop_bits = 1
> };
>
>+struct vcpu idlevcpu0;
>+
> void start_kernel(void)
> {
>     unsigned char *cmdline;
>@@ -280,7 +282,8 @@
>
> printk("About to call scheduler_init()\n");
>     scheduler_init();
>-    idle_vcpu[0] = (struct vcpu*) ia64_r13;
>+    ia64_r13 = (void *)&idlevcpu0;
>+    idle_vcpu[0] = &idlevcpu0;
>     idle_domain = domain_create(IDLE_DOMAIN_ID, 0);
>     BUG_ON(idle_domain == NULL);
>
>
>
>
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