Re: [Xen-devel] [PATCH v6 11/24] x86/xen_hello_world.xsplice: Test payload for patching 'xen_extra_version'.

[Julien Grall <julien.grall@xxxxxxx>]

Hi Konrad,

On 07/04/16 04:49, Konrad Rzeszutek Wilk wrote:
> This change demonstrates how to generate an xSplice ELF payload.
>
> The idea here is that we want to patch in the hypervisor
> the 'xen_version_extra' function with an function that will
> return 'Hello World'. The 'xl info | grep extraversion'
> will reflect the new value after the patching.
>
> To generate this ELF payload file we need:
>   - C code of the new code (xen_hello_world_func.c).
>   - C code generating the .xsplice.funcs structure
>     (xen_hello_world.c)
>   - The address of the old code (xen_extra_version). We
>     retrieve it by  using 'nm --defined' on xen-syms.
>   - The size of the new and old code for which we use
>     nm --defined -S on our code and xen-syms respectively.
>
> There are two C files and one header files generated
> during build. One could make this one C file if the
> size of the newly patched function size was known in
> advance (or an random value was choosen).
>
> There is also a strict order of compiling:
>   1) xen_hello_world_func.c
>   2) config.h - extract the size of the new function,
>      the old function and the old function address.
>   3) xen_hello_world.c - which contains the .xsplice.funcs
>      structure.
>   4) Link the object files in an xen_hello_world.xsplice file.
>
> The use-case is simple:
>
> $xen-xsplice load /usr/lib/debug/xen_hello_world.xsplice
> $xen-xsplice list
>   ID                                     | status
> ----------------------------------------+------------
> xen_hello_world                           APPLIED
> $xl info | grep extra
> xen_extra              : Hello World
> $xen-xsplice revert xen_hello_world
> Performing revert: completed
> $xen-xsplice unload xen_hello_world
> Performing unload: completed
> $xl info | grep extra
> xen_extra              : -unstable
>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
For the ARM bits:

Acked-by: Julien Grall <julien.grall@xxxxxxx>

Regards,

--
Julien Grall

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