Creating new ROM sessions at runtime

[Norman Feske]

Hi Georg,

> On Thu, Jan 14, 2016 at 12:29:49PM +0100, Georg Guba wrote:
>> I'm trying to start new child components from ELF binaries received at
>> run-time and stored in a server-local buffer. Basically, I am trying to
>> implement a server that can receive task descriptions and matching binaries
>> and then start them at run-time (disregarding security concerns for the
>> moment).

On 14.01.2016 17:06, Christian Helmuth wrote:
> The first idea that comes to my mind is: Implement a ROM server
> "elf_rom", which stores the retrieved ELF binaries in dataspaces
> allocated from its RAM session.

As long as your executable binary is statically linked, the problem can
be solved in an easier way: When creating a subsystem by constructing a
'Child' object, you have to pass a dataspace capability for the ELF
binary. You can simply allocate a new RAM dataspace (i.e., creating an
'Attached_ram_dataspace'), copy the ELF binary into the dataspace and
pass the dataspace capability to the constructor of the 'Child'. There
is no need to create a ROM server.

However, if you want to start dynamically linked executables, the child
component will initially start the dynamic linker, which, in turn,
requests the executable binary along with the needed shared libraries as
ROM sessions. Your server would need to respond to those requests by
handing out ROM-session capabilities. As an example for this approach, I
recommend you to look at the loader [1], which seems to be similar to
the server you are building.

[1]
https://github.com/genodelabs/genode/tree/master/repos/os/src/server/loader

Cheers
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

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