Re: [Xen-devel] Re: Continuing problems booting

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

M A Young wrote:
> On Sun, 22 Feb 2009, M A Young wrote:
>
> > On Sat, 21 Feb 2009, Jeremy Fitzhardinge wrote:
> >
> > > > ...
> > > > (XEN) d0:v0: unhandled page fault (ec=0000)
> > > > (XEN) Pagetable walk from 0000000000000028:
> > > > (XEN)  L4[0x000] = 0000000000000000 ffffffffffffffff
> > > > (XEN) domain_crash_sync called from entry.S
> > > > (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
> > > > (XEN) ----[ Xen-3.3.1  x86_64  debug=n  Not tainted ]----
> > > > (XEN) CPU:    0
> > > > (XEN) RIP:    e033:[<ffffffff816c5315>]
> > > What does this correspond to in the kernel?
> > >
> > > $ gdb vmlinux
> > > (gdb) x/i 0xffffffff816c5315
> > 0xffffffff816c5315 <xen_start_kernel+16>:    mov    %gs:0x28,%rax
> This is from
> 0xffffffff816c5305 <xen_start_kernel>:    push   %rbp
> 0xffffffff816c5306 <xen_start_kernel+1>:    mov    %rsp,%rbp
> 0xffffffff816c5309 <xen_start_kernel+4>:    push   %rbx
> 0xffffffff816c530a <xen_start_kernel+5>:    sub    $0x18,%rsp
> 0xffffffff816c530e <xen_start_kernel+9>:
>     mov    0x333e23(%rip),%rdi        # 0xffffffff819f9138 
> <xen_start_info>
> 0xffffffff816c5315 <xen_start_kernel+16>:    mov    %gs:0x28,%rax
> 0xffffffff816c531e <xen_start_kernel+25>:    mov    %rax,-0x18(%rbp)
> 0xffffffff816c5322 <xen_start_kernel+29>:    xor    %eax,%eax
> 0xffffffff816c5324 <xen_start_kernel+31>:    test   %rdi,%rdi
> 0xffffffff816c5327 <xen_start_kernel+34>:
>     je     0xffffffff816c5827 <xen_start_kernel+1314>
> 0xffffffff816c532d <xen_start_kernel+40>:
>     movl   $0x1,0x333df9(%rip)        # 0xffffffff819f9130 
> <xen_domain_type>
> ...
>
> which is generated if CONFIG_CC_STACKPROTECTOR=y (also 
> CONFIG_CC_OPTIMIZE_FOR_SIZE=y though I don't know is the latter is 
> important). If these aren't set, the compiler produces differnt code, 
> and the boot process gets a bit further before crashing. 
Hm, yes, I guess there's something to stop stack-protector from adding 
stuff to xen_start_kernel().
But I'm more interested in the crash you see when you have stack 
protector off.  What are the symptoms?
   J

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