start_info content for linux

start_info content for linux

[George Shuklin]

Good day.

I've digging in some strange memory/balloon related bug and I've really 
like to see start_info content on linux. I saw in source code

#ifdef CONFIG_X86_32
         mov %esi,xen_start_info
         mov $init_thread_union+THREAD_SIZE,%esp
#else
         mov %rsi,xen_start_info
         mov $init_thread_union+THREAD_SIZE,%rsp
#endif
         jmp xen_start_kernel

Pointer to start_info stored in linux global variable xen_start_info, 
but I can't find way to access it.

Is any way to get it from linux kernel? (well, except writing your own 
module).

Thanks.

Re: start_info content for linux

[Ian Campbell]

On Wed, 2012-09-26 at 09:32 +0100, George Shuklin wrote:
> Good day.
> 
> I've digging in some strange memory/balloon related bug and I've really 
> like to see start_info content on linux. I saw in source code
> 
> #ifdef CONFIG_X86_32
>          mov %esi,xen_start_info
>          mov $init_thread_union+THREAD_SIZE,%esp
> #else
>          mov %rsi,xen_start_info
>          mov $init_thread_union+THREAD_SIZE,%rsp
> #endif
>          jmp xen_start_kernel
> 
> Pointer to start_info stored in linux global variable xen_start_info, 
> but I can't find way to access it.
>
> Is any way to get it from linux kernel? (well, except writing your own 
> module).

I don't think this structure is exported to userspace, so I'm afraid it
would have to be a module, or use some sort of /dev/kmem capable
debugger (I don't know one to recommend though).

To do any serious debugging of ballooning you are probably going to need
to build a kernel with debugging added anyway though.

Ian.

Re: start_info content for linux

[Konrad Rzeszutek Wilk]

On Wed, Sep 26, 2012 at 12:32:40PM +0400, George Shuklin wrote:
> Good day.
> 
> I've digging in some strange memory/balloon related bug and I've
> really like to see start_info content on linux. I saw in source code
> 
> #ifdef CONFIG_X86_32
>         mov %esi,xen_start_info
>         mov $init_thread_union+THREAD_SIZE,%esp
> #else
>         mov %rsi,xen_start_info
>         mov $init_thread_union+THREAD_SIZE,%rsp
> #endif
>         jmp xen_start_kernel
> 
> Pointer to start_info stored in linux global variable
> xen_start_info, but I can't find way to access it.
> 
> Is any way to get it from linux kernel? (well, except writing your
> own module).

No. That is the only way.

What do you want to get out of the xen_start_kernel structure?
> 
> Thanks.
> 
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