Re: Need help with mach_printf()

[Samuel Thibault]

Svante Signell, le ven. 08 mars 2019 11:42:19 +0100, a ecrit:
> On Fri, 2019-03-08 at 11:39 +0100, Svante Signell wrote:
> > On Fri, 2019-03-08 at 11:28 +0100, Samuel Thibault wrote:
> > > Use mach_print for a start, to avoid any potential problem with vsnprintf
> > > etc.
> > > 
> > > Svante Signell, le ven. 08 mars 2019 11:16:32 +0100, a ecrit:
> > > > (cd libs; ln -s libtrivfs.so.0.3 libtrivfs.so.0)
> > > > export LD_LIBRARY_PATH=./libs
> > > > ldd /hurd/null
> > > >         libtrivfs.so.0.3 => ./libs/libtrivfs.so.0.3 (0x01029000)
> > > 
> > > If it's /dev/null that you want to debug, it's for the start of /dev/null
> > > that
> > > you
> > > need to set LD_LIBRARY_PATH. And do not set the variable then sudo to
> > > start /dev/null, sudo clears the environment.
> > 
> > So I need to do as root?
> > LD_LIBRARY_PATH=/home/srs/hurd.debs/0.9.git20190303-1.3/libfshelp-tests/libs
> >  \
> > settrans -cap /dev/null /hurd/null

That's the idea.

> Does not work :(

For a start, put a

*(int*)0 = 0;

in some initialization function of libfshelp, to make sure that
LD_LIBRARY_PATH really gets taken into account (i.e. /hurd/null should
crash). If that doesn't work then the issue is on the LD_LIBRARY_PATH
side. Perhaps you rather have to use 

settrans -cap /dev/null /usr/bin/env 
LD_LIBRARY_PATH=/home/srs/hurd.debs/0.9.git20190303-1.3/libfshelp-tests/libs 
/hurd/null

Samuel