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



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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