Hi Norman and Christian,

thank you both for your answers! I actually got Norman's approach working using a slightly modified version of the demo's launchpad. With this launchpad, all I have to do is load incoming binaries into an Attached_ram_dataspace as Norman said.

diff --git a/repos/demo/include/launchpad/launchpad.h b/repos/demo/include/launchpad/launchpad.h
index 9aa0ed5..2e319f8 100644
--- a/repos/demo/include/launchpad/launchpad.h
+++ b/repos/demo/include/launchpad/launchpad.h
@@ -268,7 +268,9 @@ class Launchpad
                           Genode::Allocator *alloc) { }
 
  Launchpad_child *start_child(const char *prg_name, unsigned long quota,
-                             Genode::Dataspace_capability config_ds);
+                             Genode::Dataspace_capability config_ds,
+                             Genode::Dataspace_capability binary_ds = 
+                               Genode::Dataspace_capability());
 
  /**
  * Exit child and close all its sessions
diff --git a/repos/demo/src/lib/launchpad/launchpad.cc b/repos/demo/src/lib/launchpad/launchpad.cc
index d60ad51..2fde521 100644
--- a/repos/demo/src/lib/launchpad/launchpad.cc
+++ b/repos/demo/src/lib/launchpad/launchpad.cc
@@ -186,7 +186,8 @@ void Launchpad::process_config()
 
 Launchpad_child *Launchpad::start_child(const char *filename,
                                         unsigned long ram_quota,
-                                        Genode::Dataspace_capability config_ds)
+                                        Genode::Dataspace_capability config_ds,
+                                        Genode::Dataspace_capability binary_ds)
 {
  printf("starting %s with quota %lu\n", filename, ram_quota);
 
@@ -212,19 +213,27 @@ Launchpad_child *Launchpad::start_child(const char *filename,
  /* lookup executable elf binary */
  Dataspace_capability  file_cap;
  Rom_session_capability rom_cap;
- try {
- /*
- * When creating a ROM connection for a non-existing file, the
- * constructor of 'Rom_connection' throws a 'Parent::Service_denied'
- * exception.
- */
- Rom_connection rom(filename, unique_name);
- rom.on_destruction(Rom_connection::KEEP_OPEN);
- rom_cap  = rom.cap();
- file_cap = rom.dataspace();
- } catch (...) {
- printf("Error: Could not access file \"%s\" from ROM service.\n", filename);
- return 0;
+ if (binary_ds == Genode::Dataspace_capability())
+ {
+ /* invalid dataspace, look up in file */
+ try {
+ /*
+ * When creating a ROM connection for a non-existing file, the
+ * constructor of 'Rom_connection' throws a 'Parent::Service_denied'
+ * exception.
+ */
+ Rom_connection rom(filename, unique_name);
+ rom.on_destruction(Rom_connection::KEEP_OPEN);
+ rom_cap  = rom.cap();
+ file_cap = rom.dataspace();
+ } catch (...) {
+ printf("Error: Could not access file \"%s\" from ROM service.\n", filename);
+ return 0;
+ }
+ }
+ else
+ {
+ file_cap = binary_ds;
  }
 
  /* create ram session for child with some of our own quota */

On 14 January 2016 at 18:11, Norman Feske <norman.feske@...1...> wrote:
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

http://www.genode-labs.com · http://genode.org

Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth

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