Re: ldd runs linux programs

On Thu, Aug 01, 2013 at 04:39:35PM +0300, Konstantin Belousov wrote:
> 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. :)
> >
> > [snip]
>
> 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.

I spent some time trying to figure out if there was any reason for this
and didn't come up with anything. Does the patch below look ok? It just
adds a couple of macros to set both the native and 32-bit compat
variable. It works properly for me for 32-bit, native, and (32-bit)
Linux executables and shared libs on an amd64 machine.

diff --git a/usr.bin/ldd/ldd.c b/usr.bin/ldd/ldd.c
index 00c8797..39f38e8 100644
--- a/usr.bin/ldd/ldd.c
+++ b/usr.bin/ldd/ldd.c
_at__at_ -49,12 +49,6 _at__at_ __FBSDID("$FreeBSD$");
 
 #include "extern.h"
 
-#ifdef COMPAT_32BIT
-#define	LD_	"LD_32_"
-#else
-#define	LD_	"LD_"
-#endif
-
 /*
  * 32-bit ELF data structures can only be used if the system header[s] declare
  * them.  There is no official macro for determining whether they are declared,
_at__at_ -76,13 +70,23 _at__at_ static void	usage(void);
 
 #define	_PATH_LDD32	"/usr/bin/ldd32"
 
+#define	LDD_SETENV(name, value, overwrite) do {		\
+	setenv("LD_" name, value, overwrite);		\
+	setenv("LD_32_" name, value, overwrite);	\
+} while (0)
+
+#define	LDD_UNSETENV(name) do {		\
+	unsetenv("LD_" name);		\
+	unsetenv("LD_32_" name);	\
+} while (0)
+
 static int
 execldd32(char *file, char *fmt1, char *fmt2, int aflag, int vflag)
 {
 	char *argv[8];
 	int i, rval, status;
 
-	unsetenv(LD_ "TRACE_LOADED_OBJECTS");
+	LDD_UNSETENV("TRACE_LOADED_OBJECTS");
 	rval = 0;
 	i = 0;
 	argv[i++] = strdup(_PATH_LDD32);
_at__at_ -121,7 +125,7 _at__at_ execldd32(char *file, char *fmt1, char *fmt2, int aflag, int vflag)
 	}
 	while (i--)
 		free(argv[i]);
-	setenv(LD_ "TRACE_LOADED_OBJECTS", "yes", 1);
+	LDD_SETENV("TRACE_LOADED_OBJECTS", "yes", 1);
 	return (rval);
 }
 #endif
_at__at_ -210,15 +214,15 _at__at_ main(int argc, char *argv[])
 		}
 
 		/* ld.so magic */
-		setenv(LD_ "TRACE_LOADED_OBJECTS", "yes", 1);
+		LDD_SETENV("TRACE_LOADED_OBJECTS", "yes", 1);
 		if (fmt1 != NULL)
-			setenv(LD_ "TRACE_LOADED_OBJECTS_FMT1", fmt1, 1);
+			LDD_SETENV("TRACE_LOADED_OBJECTS_FMT1", fmt1, 1);
 		if (fmt2 != NULL)
-			setenv(LD_ "TRACE_LOADED_OBJECTS_FMT2", fmt2, 1);
+			LDD_SETENV("TRACE_LOADED_OBJECTS_FMT2", fmt2, 1);
 
-		setenv(LD_ "TRACE_LOADED_OBJECTS_PROGNAME", *argv, 1);
+		LDD_SETENV("TRACE_LOADED_OBJECTS_PROGNAME", *argv, 1);
 		if (aflag)
-			setenv(LD_ "TRACE_LOADED_OBJECTS_ALL", "1", 1);
+			LDD_SETENV("TRACE_LOADED_OBJECTS_ALL", "1", 1);
 		else if (fmt1 == NULL && fmt2 == NULL)
 			/* Default formats */
 			printf("%s:\n", *argv);