Loading shared objects in an l4env_freebsd application

Frank Mehnert fm3 at os.inf.tu-dresden.de
Fri Jun 10 11:11:35 CEST 2005

On Friday 10 June 2005 10:43, Derick Swanepoel wrote:
> On 6/9/05, Frank Mehnert <fm3 at os.inf.tu-dresden.de> wrote:
> > If you need the libraries of the l4env_freebsd_mode, it should be
> > possible to add these libraries using the LIBS= parameter. If you
> > look at the appropriate Makefile you will see, that libloaderif.a
> > contains only the client stub of the loader IDL and therefore has
> > nothing to do with the shared library stuff.
> >
> > The point is that you should start from the loader mode and enhance
> > this mode for your needs since the loader mode uses a different
> > startup strategy than the sigma0 mode.
> Thanks for the advice. I have created a new mode to combine the loader
> mode with what I need from l4env_freebsd, and I can successfully
> compile and link my application. Unfortunately it causes a double
> pagefault when loaded...:
> loader  | "(nd)/fiasco/ds/test" is a valid binary image
> loader  | Setting libpath to (nd)/fiasco/ds/
> exec    | test: Loading
> exec    | test: Saved 457726 bytes of symbols
> exec    | libloader.s.so: Relocating to 0000e000
> exec    | libloader.s.so: Linking
> exec    | libloader.s.so: Relocating entry 000058d0 => 000138d0
> exec    | libloader.s.so: Setting section flag 0800
> exec    | test: Setting section flag 0800
> loader  | test: Starting l4env-style application
> loader  | test,#11: Starting at l4loader_init (00014080)
> loader  | test,#11: Double PF (r) at 00000000 eip 00000000 (11.00)

Ok, this is a pagefault in the loader library. Please look at the file
l4/pkg/loader/server/src/app.c and search for APP_ADDR_LIBLOADER. Take
that address as the base for libloader.s.so. Subtract that address from
the pagefault address. The result is the offset into the loader lib. Do

  objdump -ld libloader.s.so | less

and search for the offset. Then scroll a little bit around and look
for lines of source code contained in the listing. Or simply post the
listing here.

## Dept. of Computer Science, Dresden University of Technology, Germany ##
## http://os.inf.tu-dresden.de/~fm3                                     ##
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