Re: ldd runs linux programs

On Wed, Jul 31, 2013 at 10:12:31PM -0400, Mark Johnston wrote:
> On Mon, Jul 29, 2013 at 10:54:49PM +0200, Mateusz Guzik wrote:
> > On Mon, Jul 29, 2013 at 11:56:25AM -0400, Mark Johnston wrote:
> > > > 127276 suggests running the binary as is (which I don't like) and
> > > > achieves this with a hacky way. So if we really want to do this, the
> > > > patch should be reworked to detect Linux binaries properly.
> > > > 
> > > > In general we should gain linux_ldd (like linux_kdump) and our ldd
> > > > should work only on FreeBSD binaries. The last part is achieved with my
> > > > patch.
> > > > 
> > > > markj, are you working on this?
> > > 
> > > Not really; my original fix for this problem was essentially the same as
> > > yours. That is, just change ldd(1) to bail if the OS ABI byte isn't
> > > equal to ELFOSABI_FREEBSD. That's the change I have committed in my
> > > local tree right now.
> > > 
> > > Then I thought I'd try to get ldd to work properly with Linux binaries
> > > as well, but wasn't sure what the right approach should be. As the above
> > > PR suggests, the easy thing to do is to just pass
> > > LD_TRACE_LOADED_OBJECTS and not LD_32_TRACE_LOADED_OBJECTS for 32-bit
> > > ELF objects if the OS isn't FreeBSD. This feels somewhat hacky to me,
> > > but I didn't really see another approach.
> > > 
> > > That said, I think your patch should be committed since it's clearly an
> > > improvement over the current behaviour. I'm willing to test and commit
> > > it, and clean up the open PRs. If you could expand on the right way to
> > > handle Linux binaries, I'd be willing to implement and commit that too.
> > > I don't quite understand your reference to linux_kdump though - I have
> > > no such program on my laptop running CURRENT, and ktrace+kdump seem to
> > > work fine with the Linux binaries under /compat/linux.
> > > 
> > 
> > Well, there was linux_kdump in ports but it apparently got obsolete as
> > necessary support for included in our regular kdump.
> > 
> > So it may make sense to teach our ldd how to deal with Linux binaries
> > for consistency, but its unclear for me if this is better than providing
> > linux_ldd. Also there is the problem of (not) appending /compat/linux to
> > printed paths (for Linux binaries the kernel performs file lookups against
> > /compat/linux first). I'm not that interested in this problem though. :P
> 
> What do you think of the patch below, which just sets both variables in
> the compat case? It's somewhat less intrusive than the patch in the PR.
> If that's no good then I'll just commit your original patch; I really
> just want to fix the fact that the example pipeline in the ldd(1) man
> page starts a GTK program (some Adobe Flash thingy to be specific) when
> run in /usr/local/bin on my desktop machine. :)
> 
> Thanks,
> -Mark
> 
> diff --git a/usr.bin/ldd/ldd.c b/usr.bin/ldd/ldd.c
> index 00c8797..71e9c8d 100644
> --- a/usr.bin/ldd/ldd.c
> +++ b/usr.bin/ldd/ldd.c
> _at__at_ -51,6 +51,7 _at__at_ __FBSDID("$FreeBSD$");
>  
>  #ifdef COMPAT_32BIT
>  #define	LD_	"LD_32_"
> +#define	LD_COMPAT_ "LD_"
>  #else
>  #define	LD_	"LD_"
>  #endif
> _at__at_ -211,6 +212,13 _at__at_ main(int argc, char *argv[])
>  
>  		/* ld.so magic */
>  		setenv(LD_ "TRACE_LOADED_OBJECTS", "yes", 1);
> +#ifdef COMPAT_32BIT
> +		/*
> +		 * Set this for the benefit of runtime linkers that don't know
> +		 * we're in compat mode.
> +		 */
> +		setenv(LD_COMPAT_ "TRACE_LOADED_OBJECTS", "yes", 1);
> +#endif
>  		if (fmt1 != NULL)
>  			setenv(LD_ "TRACE_LOADED_OBJECTS_FMT1", fmt1, 1);
>  		if (fmt2 != NULL)

I do not understand this COMPAT_32BIT business in ldd(1). Its only
application seems to preventing ldd 32bit binary from amd64 host to
work on i386 ?

IMO, both LD_TRACE and LD_32_TRACE should be passed unconditionally
always.  I do not see any harm of doing this.